Zebra mussels have been found in Mille Lacs Lake! Please be very careful and follow exotic species control guidelines when leaving the lake! In 2005, scuba divers found four zebra mussels. The mussels that were found were too isolated to be part of a breeding population. However, it is unlikely that divers would have found that many zebra mussels without a breeding population existing somewhere in the system. The discovery of zebra mussels in Mille Lacs Lake is potentially problematic. Zebra mussels are capable of obtaining extremely high densities. Future impacts to native invertebrates, walleye spawning areas, swimming beaches, the bait industry, and the local economy in general are not known. A monitoring program will be developed to document any increase in zebra mussel density over time. That monitoring program will also allow early detection of other possible exotics such as rusty crayfish. Walleye catch rates in the gill nets were a little lower than usual for Mille Lacs. This was due to the missing 2000 and 2001 year-classes. However, very strong 2002 and 2003 year-classes are making up the difference. As a result, numbers of walleye under 17 inches are high, as are numbers of walleye over 20 inches. Young-of-the-year walleye were abundant in both trawl and electrofishing samples.Yellow perch are also doing very well. Gill net catches are above average and anglers caught many large perch in the fall of 2005 and winter of 2005-2006. Forage-sized perch are also abundant, leading to very good condition in the predator species such as walleye.Tullibee numbers are showing signs of recovery after a serious decline from 1998-2002. Tullibee harvest has been restricted since that time. A plan was developed to reopen sport netting and return bag limits to statewide regulations. This plan has since been put on hold with recent discovery of zebra mussels. Northern pike numbers appear to be increasing, most likely as a result of the special regulations. The 24-36 inch protected slot may have discouraged anglers interested only in harvesting pike. There is a pike tagging study underway to determine the size of the population.Muskellunge continue to thrive in Mille Lacs Lake. Each year, more fish over 50 inches are reported. In 2006, a muskellunge survey will be conducted to compare growth of the two strains, look at size distributions, and measure the degree of natural reproduction. Fishing pressure for muskellunge has increased with the quality of the fish.Smallmouth bass are also continuing to increase in popularity, although no longer as fast as the muskellunge. The smallmouth population appears to be much larger than expected in 1999. In 1999, visual surveys of spawning areas were used to get a general feel for the abundance of smallmouth bass. In 2005, scuba divers found numbers of smallmouth bass spawning in deep water. These deep-water spawners were distributed throughout the lake wherever suitable habitat could be found. Smallmouth bass still maintain a high average size of about 17 inches.
","lengths":{},"fishCatchSummaries":[{"gear":"Standard gill nets","totalCatch":345,"species":"TLC","totalWeight":102.6,"gearCount":32,"CPUE":"10.78","quartileWeight":"0.4-0.5","quartileCount":"4.9-17.6","averageWeight":"0.30"},{"totalCatch":1,"species":"BUB","gear":"Standard gill nets","quartileWeight":"1.1-2.1","quartileCount":"0.0-0.2","averageWeight":"0.40","gearCount":32,"totalWeight":0.4,"CPUE":"0.03"},{"totalCatch":49,"species":"NOP","gear":"Standard gill nets","quartileWeight":"2.4-4.3","averageWeight":"5.93","quartileCount":"0.9-4.3","totalWeight":290.4,"gearCount":32,"CPUE":"1.53"},{"totalCatch":4,"species":"BLC","gear":"Standard gill nets","quartileWeight":"0.2-0.5","averageWeight":"0.50","quartileCount":"0.1-0.7","gearCount":32,"totalWeight":2,"CPUE":"0.12"},{"gear":"Standard gill nets","totalCatch":4,"species":"WTS","totalWeight":0.9,"gearCount":32,"CPUE":"0.12","quartileWeight":"1.6-2.1","averageWeight":"0.23","quartileCount":"0.8-2.4"},{"quartileWeight":"3.3-8.0","averageWeight":"39.65","quartileCount":"0.0-0.1","totalWeight":79.3,"gearCount":32,"CPUE":"0.06","totalCatch":2,"species":"MUE","gear":"Standard gill nets"},{"species":"WAE","totalCatch":414,"gear":"Standard gill nets","averageWeight":"2.15","quartileCount":"3.3-14.8","quartileWeight":"0.9-1.5","CPUE":"12.94","totalWeight":889.3,"gearCount":32},{"quartileWeight":"0.8-1.5","averageWeight":"1.96","quartileCount":"0.0-0.2","totalWeight":45.1,"gearCount":32,"CPUE":"0.72","totalCatch":23,"species":"SMB","gear":"Standard gill nets"},{"averageWeight":"0.60","quartileCount":"N/A","quartileWeight":"N/A","CPUE":"0.03","gearCount":32,"totalWeight":0.6,"species":"BLG","totalCatch":1,"gear":"Standard gill nets"},{"species":"YEP","totalCatch":4362,"gear":"Standard gill nets","quartileCount":"9.9-57.1","averageWeight":"0.21","quartileWeight":"0.2-0.3","CPUE":"136.31","gearCount":32,"totalWeight":895.7},{"gearCount":32,"totalWeight":21.7,"CPUE":"1.56","quartileWeight":"0.3-0.6","quartileCount":"0.1-1.1","averageWeight":"0.43","gear":"Standard gill nets","totalCatch":50,"species":"RKB"}],"surveyDate":"2005-09-18","surveyID":"113724","surveyType":"Standard Survey","headerInfo":{"wb_name":"Mille Lacs","wb_type":"Lake","wb_alt_name":"","id_date":"2005-09-18","wb_id":"48000200","survey_type":"Population Assessment","survey_id":"113724","county":"Mille Lacs"}},{"surveySubType":"Large Lake Survey","narrative":"Mille Lacs Lake is a 132,516-acre glacially-formed lake in east-central Minnesota. Fewer than 20 streams from a 240,000 acre watershed are tributary to the lake. The Rum River is the only outlet. Approximately 70 percent of the 85 miles of shoreline consists of suitable walleye spawning habitat exposed to wind and waves. Wind mixes water freely from top to bottom, resulting in little thermal stratification and good oxygen distribution at all depths. Offshore habitats include sand and mud flats, rock reefs, and a few small exposed islands. A few marsh areas exist in the southern part of the lake, and along some tributaries.
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\nThe Mille Lacs Lake gamefish community is primarily composed of walleye, yellow perch, northern pike, muskellunge, and smallmouth bass. Tullibee is an important forage species, and common minnow species include spottail shiner and mimic shiner. The recent invasion of zebra mussels is expected to create changes in Mille Lacs Lake. It will be important for anglers and other boaters to follow guidelines to prevent the spread of zebra mussels to other waters.
\n
\nWalleye
\nWalleye sampling in 2008 produced mixed indices of abundance. Gill net catch rates in the inshore nets were the second lowest recorded, with only 2007 catch rates being lower. The catch rate in 2007 appeared low based on unusual patterns in the geographic distribution of walleye in the nets, and also appeared to be low compared to the population estimate from the spring of 2008. Therefore, the 2008 catch rates may represent the lowest abundance of walleye recorded near shore. Walleye catch rates in the offshore nets were near average. The 2002 year class was poorly represented in the inshore gill nets, but was relatively abundant offshore.
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\nThe catch of walleye over 20 in has shown a decline in both inshore and offshore nets in recent years. The protected slots that have been implemented in recent years appear to have resulted in short-term increases in larger walleye by reducing the kill of older females. Catches of larger walleye have declined in both the inshore and offshore nets in recent years. The 2000 and 2001 year classes should be contributing to the population of walleye over 20 in, but those year classes are both very weak.
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\nIndices of reproduction supported another year of above average recruitment. The CPE of YOY walleye in gill nets has been consistently higher since special regulations protecting larger fish have been in place. Higher indices of YOY walleye in recent years were also observed in the trawl and electrofishing samples. However, recent strong year classes appeared to have failed to persist when compared to long-term averages. The 2002 and 2003 year classes have both experienced relatively high fishing mortality, which could have driven abundance down. However, other year classes in the past also experienced high exploitation without showing the same degree of decline over time. Unrepresentatively low gill net catches observed in 2007, and perhaps 2008, would also explain some of the decline. Unidentified mechanisms associated with the increase in larger walleye may also play a part.
\n
\nNorthern Pike
\nNorthern pike sampled by the pike gill nets tended to be older but smaller than northern pike sampled in the standard inshore gill nets. The pike nets had a relatively high proportion of pike age 4 and older that were less than 28 in. One possible explanation would be that there were more males in the pike nets. However, sex ratios were about equal. Pike in the inshore gill nets were 57% male and pike in the pike nets were 53% male. Habitat may be a better explanation. The inshore gill nets are often set in areas with little or no vegetation, while pike nets are usually set in or immediately adjacent to vegetation. Larger pike are less dependent on vegetation for cover, and so may be expected more often in gill nets set in areas free of plant growth. The smaller sample size associated with the inshore nets may also have played a role.
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\nThere were more age 1 northern pike in the gill nets than in any previous year. Increased reproduction of northern pike may have been a result of increased egg production by protecting larger females with slot limits. Numbers and biomass of mature females in the inshore gill nets increased soon after protected slots were implemented in 1998, followed by increases in numbers of YOY and age 1 pike. The recruitment dynamics for northern pike appeared very similar to those observed in the walleye after the protected slots were enacted.
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\nYellow Perch
\nAlthough the CPE of yellow perch in the gill nets increased from 2007, the CPE was about average for recent years. Numbers of perch over 9 in were average as well. A strong 2006 year class should begin to contribute more perch over 9 in next year. The 2002 year class, which was the strongest year class since 1996, is growing out of the fishery, and represented only 5% of the catch in the inshore gill nets.
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\nSmall yellow perch provided abundant forage in 2008, mostly as age 1. The 2008 year class was not expected to do well because of the late spring, cold summer, and suppression from the large 2007 year class. While catches of YOY perch in the trawl were below the median, they were higher than expected. Growth rate for small perch was predictably slow, given their abundance and the cool summer.
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\nTullibee
\nContrasting with the perch, tullibee were expected to benefit from the cool summer. The numbers of YOY tullibee in the trawl were the highest ever observed. Catches of YOY tullibee were 12 times higher than in 2007, and 36 times higher than the median since 1992. Also, the abundance of YOY tullibee in fine-mesh gill nets set throughout the summer were the highest observed in three years of forage netting. This apparently very strong year class should provide high quality forage for walleye and other large predators for several years.
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\nAlthough catches of tullibee vary from year to year, they appear to vary differently in inshore and offshore areas. Inshore catches have been almost entirely age 1 tullibee since 2003. In several years, the inshore catch of age 1 tullibee exceeded the 1987-1997 median, but in subsequent years, those year classes were absent from the inshore gill nets. In the offshore gillnets, these same year classes demonstrated relatively good concordance from year to year. Variability in tullibee vulnerability to the different surveys may be influenced by environmental conditions that affect movement, geographic or vertical distribution, or possibly even mortality in different manners. Tullibee numbers have probably declined, but perhaps not to the extent represented by changes observed in the inshore gill nets.
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\nOther Species
\nA number of recent warm summers may be affecting the abundances of temperature sensitive species. Obvious declines in abundance have been observed for burbot and tullibee, while more subtle declines may be occurring for white sucker. On the other hand, species like smallmouth bass are showing a gradual increase in abundance as warmer temperatures lead to more favorable environments for warmwater species. Increases in the abundance of largemouth bass and other centrarchids are expected, but most of these species are not sampled well. Interestingly, rock bass, which might be expected to increase in abundance, seem to have peaked in the 1990s, and may now be in a period of decline.
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The Mille Lacs Lake gamefish community is primarily composed of walleye, yellow perch, northern pike, muskellunge, and smallmouth bass. Other gamefish include largemouth bass, bluegill, pumpkinseed and black crappie. Common minnow species include spottail shiner and mimic shiner. Tullibee are also present and an important component of the fish community. Invasive animal species include zebra mussel, Chinese mystery-snail, banded mystery-snail, and spiny water flea. Curlyleaf pondweed and Eurasion watermilfoil are well established in the lake.
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\nCreel Survey
\nFishing effort for the2009-2010 winter season was 1.8 million angler-hours (ang-hrs), about 5% above average. Open water 2010 fishing effort was 1.3 million ang-hrs, about 12% below average. Pressure during the open water season was low in the first half of June and the first half of July, but close to average for the rest of the season.
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\nWalleye fishing was better in 2010 than in 2009 or 2008. Harvest was 226,000 lbs and total kill was 271,000 lb, approximately twice the angler walleye kill of 2009. Anglers released another 625,000 lb of walleye. Most of the harvested walleye were age 3 and age 4.
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\nAnglers harvested 3,100 lb of northern pike, and released 49,000 lb. Total kill for pike was 5,600 lb. Northern pike regulations have changed in 2011 to a 27-40 protected slot with one of 40 inches allowed. The bag limit remains at 3.
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\nYellow perch harvest was 55,000 lb. Tullibee harvest was 15,400 lb, which was the highest observed since the bag limits were reduced to 10 in 2003. Anglers caught 48,000 smallmouth bass in 2010, which was the highest ever observed for Mille Lacs Lake.
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\nFall Assessment
\nWalleye catch per effort (CPE) in the inshore gillnets was 10.8 fish/net and 22.9 lb/net. In offshore nets, walleye CPE was 18.3 fish/net and 41.4 lb/net. The CPE of walleye longer than 20 inches, which peaked around 2002, increased sharply in the offshore nets to the highest observed. In the inshore nets, CPE of larger walleye remained at about 3 per net, which was well below peak values of close to 5 per net from 2000-2006. As observed in recent years, the 2000, 2001, and 2004 year classes were poorly represented in the gill nets, while 2007 and 2008 appeared strong. Early indications from gill nets are that the 2009 year class may be relatively weak, although catches of 2009 walleye were closer to average in electrofishing surveys. The proportion of mature walleyes that were male in inshore gill nets was nearly 50%. The number of mature males sampled in the inshore gill nets may be stabilizing after several years of decline, but should be watched closely. Walleye growth was above average for female walleye and smaller males, and about average for males aged 4-6. Walleye condition was average for walleye from 14-20 inches, and slightly above average for large and smaller fish.
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\nNorthern pike CPE in the inshore gill nets was the highest observed since 32 nets were implemented in 1983 at 2.2 fish/net. The average weight of northern pike was 6.0 lbs. Inshore nets sampled 8 different year classes, with most of the fish from the 2007 and 2008 year classes. After two consecutive years of record catches of age 1 pike in the gill nets, no age 1 pike were caught in 2010. Since protected slot regulations went into effect in 1998, the number of pike over 28 inches initially increased, but now appear stable. Although the number of pike greater than 28 in did not increase, the number and size of mature females did increase, and the weight of mature females in the gill nets jumped 50% from 205 lb to 310 lb. This was due to an increase in the number of small mature females from heavy recruitment, and an increase in the number of pike over 35 inches. In 2009, there were only three pike over 35 inches in the inshore gill nets, but 11 pike over 35 inches in the 2010 survey. The increase in smaller pike is probably real, while the increase in large pike may be a function of small sample sizes.
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\nYellow perch CPE in the inshore gillnets was 60.8 fish/net and 15.0 lb/net. Gill net CPE of perch larger than 9 in has remained about the same for the last four years. In the offshore nets, perch CPE was 41.5 fish/net and 11.9 lb/net.
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\nTullibee CPE was 11.4 fish/net and 4.9 lb/net in the inshore nets and 27.1 fish/net and 17.2 lb/net in the offshore nets. Tullibee have experienced several years of good recruitment, believed to be associated with cooler summers and falls. The result has been more tullibee in the lake as forage, and increased catches by winter anglers.
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\nOther species were also caught in standard gill nets, generally in low numbers. Some species, such as burbot and white sucker, showed declining trends. The 2010 survey was the first year in which no burbot were sampled in gill nets. Catches of smallmouth bass and rock bass both dropped significantly from 2009 . This was likely the result of these species being very catchable in 2009, and much less so in 2010, and does not indicate a sudden drop in actual abundance. A spring assessment of smallmouth bass found the abundance of smallmouth bass to be about three to four times higher than in 2009. The size structure of the smallmouth bass was unchanged, with more than half the bass larger than 17 inches.
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\nThe forage base appeared strong. Young-of-year yellow perch were very high in the trawl . Abundance of shiners, YOY perch, and YOY tullibee were all high in the forage gill nets as well. Abundant forage should result in good body condition for walleye, and may allow increased survival of juvenile walleye.
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\nInvasive Species
\nZebra mussel density increased to 14/ft2, which was about 3 times higher than in 2009 and 175,000 times higher than in 2005 . Veliger (larval zebra mussels) densities were up to 30 times higher in 2010 than in the previous two years. The counts of adult zebra mussels in 2011 are expected to increase substantially.
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\nThe abundance of spiny water flea also increased in 2010. Spiny water flea was found in Mille Lacs for the first time in 2009. September density increased from 0.3/liter in 2009 to 10.3/liter in 2010. Abundance was highest in September, and spiny water fleas were observed in every September sample in 2010.
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\nMore detailed reports are available at http://www.dnr.state.mn.us/areas/fisheries/aitkin/index.html
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\n
The Mille Lacs Lake game fish community is primarily composed of walleye, yellow perch, northern pike, muskellunge, and smallmouth bass. Other game fish include largemouth bass, bluegill, pumpkinseed and black crappie. Common minnow species include spottail shiner and mimic shiner. Invasive animal species include common carp, zebra mussel, Chinese mystery-snail, banded mystery-snail, and spiny water flea. Curlyleaf pondweed and Eurasian watermilfoil are well established in the lake.
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\nCreel Survey
\nFishing effort for the 2010-2011 winter season was 1.78 million angler-hours (ang-hrs), about 3% above average. Open water 2011 fishing effort was 1.16 million ang-hrs, and was about 18% below average. Pressure and catch during the State government shutdown, which went from July 1 through July 20, was estimated based on data from the first seven days prior to the shutdown and the first seven days immediately after the shutdown.
\nWalleye harvest declined slightly from 2010 levels. Harvest was 188,400 lbs and total kill was 230,200 lb, a 15% decrease from 2010. Anglers released an additional 860,000 lb of walleye, which was almost a 40% increase over 2010. Most of the harvested walleye were age 3 and age 4.
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\nAnglers harvested 5,900 lb of northern pike, and released 77,000 lb. Total kill for pike was 9,800 lb. Northern pike regulations changed in 2011 to a 27-40 inch protected slot with one over 40 inches allowed in a possession limit of 3 fish.
\nYellow perch harvest was 83,400 lb. Tullibee harvest was 55,500 lb, which was the highest observed since the bag limits were reduced to 10 fish in 2003. Anglers caught 50,900 smallmouth bass in 2011, which was the highest ever observed for Mille Lacs Lake.
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\nFall Assessment
\nWalleye catch per effort (CPE) in the inshore gillnets was 9.7 fish/net and 16.1 lb/net, the second lowest historically observed. In offshore nets, walleye CPE was 14.5 fish/net and 28.4 lb/net, which are the second and third lowest, respectively. The CPE of walleye longer than 20 inches, which peaked around 2002, decreased to moderate levels in the offshore nets. In the inshore nets, CPE of larger walleye decreased to around 2 per net, which is well below peak values of close to 5 per net from 2000-2006. As observed in recent years, the 2000, 2001, 2004, and now the 2009 year classes were poorly represented in the gill nets, while 2005 through 2008 appear average. Early indications from electro-fishing suggest that the 2010 and 2011 year classes have the potential to be average to above average. The proportion of mature walleyes that were male in inshore gill nets was nearly 50%. The number of mature males sampled in the inshore gill nets may be stabilizing after several years of decline, but should be watched closely. Walleye growth was below average for female walleye and smaller males, and about average for males ages 4-6. Walleye condition was below average at all sizes.
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\nThe northern pike CPE of 1.9 fish/net in the inshore gill nets remained at near historical highs since 32 nets were implemented in 1983. The average weight of northern pike was near average at 5.3 lbs. Inshore nets sampled 10 year classes, with most of the fish from the 2009 and 2008 year classes. Since protected slot regulations went into effect in 1998, the number of pike over 28 inches initially increased, but now appears stable. Thirty-five percent of the northern pike caught in the inshore nets were over 28 inches in length. Mature female pike weight in the inshore nets decreased 40%, from the 2010 historical high of 310 lbs to 187 lbs in 2011, which was still in the top third of weight observed since 1986. Some of the decrease in northern pike observed in 2011 fall gill nets may be due to increased harvest for the year.
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\nYellow perch CPE in the inshore gillnets was 44 fish/net and 11.0 lb/net. Gill net CPE of perch larger than 9 in has remained about the same for the last five years and was at around 13 fish/net in 2011. In the offshore nets, perch CPE was 34.0 fish/net and 10.4 lb/net.
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\nTullibee CPE declined sharply to 1.6 fish/net and 0.6 lb/net in the inshore nets and declined to a moderate 15.6 fish/net and 12.9 lb/net in the offshore nets. Tullibee have experienced several years of good recruitment, believed to be associated with cooler summers and falls. The result has been more tullibee in the lake as forage, and increased catches by winter anglers. The difference in magnitude between the inshore and offshore catches in 2011 may reflect a diminished population that is no longer over-flowing into the less desirable habitat of the near shore region, or a behavioral shift due to other environmental factors.
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\nOther species were also caught in standard gill nets, generally in low numbers. Burbot continue to exhibit declining numbers, and are now only occasionally observed in the assessment nets. Rock bass increased to average levels in 2011. Smallmouth bass catch rose from 0.3 fish/net in 2010 to 1.0 fish/net in 2011, the second highest level observed in the inshore gill nets. It's not likely that the smallmouth bass population actually increased by a factor of three over the course of a year, so most of the increase is likely due to differences in catchability between 2010 and 2011. Trends over the last decade show an increasing smallmouth bass population in the lake.
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\nThe forage gill nets showed weak numbers of age 0 tullibee and moderate numbers of yellow perch at all ages. Age 1 and age 2 tullibee were at moderate levels. Age 0 spottail shiners, and bluntnose minnows were not observed in the forage gill nets. Older spottail shiners were observed at relatively low levels. The size of YOY perch was below average in both the trawl and the forage gill nets. Reduced forage levels help explain the low condition observed in fall walleyes and suggest an increased propensity for a strong walleye bite for recreational anglers until forage stocks are replenished in early summer.
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\nInvasive Species
\nZebra mussel density increased to 920/ft2, which was about 65 times higher than in 2010 and over ten million times higher than in 2005. Veliger (larval zebra mussels) densities decreased from 2010 levels, however, July counts were not performed due to the State government shutdown. The counts of adult zebra mussels have not peaked and 2012 counts should continue to increase.
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\nThe overall abundance of spiny water flea appears to have also increased in 2011, despite no counts during the July State government shutdown. Spiny water flea was found in Mille Lacs for the first time in 2009. Peak density increased from 0.3/liter in September 2009 to 10.3/liter in September 2010 to 11.5/liter in June 2011. Spiny water fleas were observed in samples from June through September. Late May was the only sampling period where spiny water fleas were not observed.
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\nMore detailed reports are available at http://www.dnr.state.mn.us/areas/fisheries/aitkin/index.html
\n
The Mille Lacs Lake game fish community is primarily composed of walleye, yellow perch, northern pike, muskellunge, tullibee, and smallmouth bass. Other game fish include largemouth bass, bluegill, pumpkinseed and black crappie. Common minnow species include spottail shiner and mimic shiner. Invasive animal species include common carp, zebra mussel, Chinese mystery-snail, banded mystery-snail, and spiny water flea. Curlyleaf pondweed and Eurasian watermilfoil are well established in the lake.
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\nCreel Survey
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\nFishing effort for the 2013-2014 winter season was 732,500 angler-hours (ang-hrs), almost 60% below average. Only trace levels of angling pressure (700 ang-hrs) were observed once walleye season closed in late February. Ice fishing pressure was severely curtailed by poor ice conditions that prevented anglers from freely accessing major portions of the lake until mid-January. Ice angling pressure was further impacted by some of the lowest harvest rates ever observed for both walleye and yellow perch.
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\nOpen water 2014 fishing effort was 597,500 ang-hrs, which is also approximately 60% below average and the lowest observed. Open water night effort was the lowest observed, mainly due to an extended night closure that was in place through late July. Open water day pressure was low throughout all periods of the summer; likely due to low walleye catch rates and restrictive regulations.
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\nWalleye harvest, for the entire season, was the lowest observed at 11,000 lbs. Total kill, which includes hooking mortality, was 23,650 lbs. Anglers released an additional 210,750 lb of walleye. Most of the harvested walleye came from the 2006 through 2008 year classes.
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\nAnglers harvested 16,500 lb of northern pike, the highest observed since 1999. The increase in northern pike harvest was likely due to liberalized regulations that began in the summer. An additional 45,000 lb of northern pike were released. Total kill for pike was 18,800 lb.
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\nYellow perch harvest was extremely low at 3,100 lb, and tullibee harvest was similarly low at 1,700 lb. Anglers caught 81,000 smallmouth bass in 2014, which was the highest ever observed for Mille Lacs Lake. Approximately 3,850 smallmouth were harvested under the newly liberalized 6 fish bag, with only one over 18 inches, regulation.
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\n
\nFall Assessment
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\nWalleye catch per effort (CPE) in the inshore gillnets was 7.1 fish/net and 11.5 lb/net. In offshore nets, walleye CPE was 13.6 fish/net and 18.3 lb/net. Catch per effort in the inshore nets remained low and was similar to the previous year. Numbers in the offshore nets decreased to the second lowest observed, while biomass decreased to the lowest observed. The bulk of the walleye catch came from one year old fish. Only age 1 and 9+ walleyes were observed at above median levels in the gill nets. The CPE of walleye longer than 20 inches decreased to 1.4/net in the inshore nets, a level not observed since1984, while the catch rate in the offshore nets, which have a much shorter history, was the lowest observed at 2.7/net. The CPE of mature males remains low in the inshore nets and is the lowest observed and continued a decreasing trend in the offshore nets. Mature female CPE was the lowest observed in both the inshore and offshore nets and continued to exhibit a decreasing trend. Walleye growth was below average for male and female walleye ages 2-4 and older males, while growth was above average for older females. Walleye condition was the lowest observed for walleye less than 14 inches and about average for walleye greater than 14 inches, suggesting that forage for small fish may be in low abundance.
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\nNorthern pike CPE in the inshore nets remained high at 2.7 fish/net and biomass in the nets increased to the second highest observed at 11.1 lb/net. The high number of pike is mainly due to strong numbers of fish from the 2010, 2012, and 2013 year classes, which resulted in a high number of fish less than 28 inches, however, fish greater than 28 inches remained near average levels. The northern pike catch in the 16 specialized northern pike gill nets increased for the third year in a row to a CPE of 9.1 fish/net and 40.6 lb/net. About 44% of the northern pike captured in the specialized nets were from the 2012 year class. While northern pike catches continue to remain low in the offshore nets (n=4), the catch rate of 0.2/net is above the 75th quartile. All four pike observed in the offshore sets were greater than 29 inches in length.
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\nYellow perch CPE increased in the inshore nets to 28.1/net and 4.3 lb/net, but is still below the 25% quartile for Mille Lacs Lake. Gill net CPE of perch larger than 9 in dropped for the third year in a row to 1.8 fish/net, which is the second lowest observed. Yellow perch CPE in the offshore nets was similar to the previous year at 25.9/net and 6.5 lb/net, with both metrics near the 25% quartile for Mille Lacs Lake.
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\nTullibee CPE increased to 7.8 fish/net and 1.9 lb/net in the inshore nets, both around the 75% quartile for Mille Lacs Lake. CPE also increased in the offshore nets to 28.2 fish/net and 19.3 lb/net. Over 60% of the tullibee observed in the inshore nets were from the 2013 year class. The offshore nets were more age-diverse with 33% of the tullibee from the 2013 year class, 21% from the 2008 year class, and 13% from the 2009 year class. The difference in magnitude between the inshore and offshore catches over the last several years may reflect a diminished lake-wide population that is no longer over-flowing into the less desirable habitat of the near shore region, or it may represent a behavioral shift into offshore regions due to other environmental factors.
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\nOther species were also caught in standard gill nets, generally in low numbers. Burbot continued to exhibit a declining trend in number, and are now only occasionally observed in the assessment nets. Rock bass declined to an average level of 0.8/net. Smallmouth bass declined to 0.8/net in the inshore nets, but remain at above average levels. Smallmouth bass continued to incrementally increase in the offshore nets and are now at the highest observed at 0.4/net. Trends over the last decade continue to suggest an increasing smallmouth bass population in the lake.
\n
\nForage gill nets showed mixed results. Young-of-the-year (YOY) yellow perch were the lowest observed in both numbers and biomass over the nine year history of the forage gill nets. Age 1 yellow perch, which were at the highest level observed as YOY, were observed at a more moderate level in 2014, presumably due to predation. Age 0 tullibee were observed at moderate numbers and biomass, while age 1 tullibee were at the highest observed. Moderate numbers of spottail shiners were also observed.
\n
\nAge 0 walleye were observed at lower numbers and biomass, while ages 1 walleye were at the highest observed. Overall, the forage nets would suggest low forage availability for smaller walleye, which is corroborated by the low condition observed in walleye less than 14 inches that were captured in the fall gill nets. Further, there would appear to be sufficient alternative forage available to larger piscivores, in the form of age 1 tullibee and yellow perch, so that the strong age 1 walleye year class should have a greater probability of getting through the remaining predatory gauntlet.
\n
\nAge 0 walleye CPE in the six electrofishing transects was below median levels for the first time since 2009 at 106.5/hr and 65.0/mile. However, this level of abundance has previously been sufficient to produce a decent year class, as long as survival is above average. Average length for age 0 walleye was 4.85 inches. Age 1 walleye CPE was the second highest observed at 46.4/hr and the third highest observed at 28.3/mile. The average length of age 1 walleye was 9.41 inches. Forage electrofishing runs of two minutes duration showed extremely low numbers of age 0 yellow perch and low to moderate numbers of age 1 yellow perch. Age 1 walleye and age 0 largemouth bass CPE was the highest observed in the four year history of forage electrofishing.
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\nTrawling was expanded in 2014 to cover more areas throughout the lake and to sample additional habitat types. Of the twenty-three locations sampled, age 0 yellow perch were the most plentiful species observed at 283.8 fish/hr, however, 99.8% were captured at a single site. Average length of the YOY yellow perch was 2.41 inches. The second most observed fish was age 0 tullibee with a CPE of 142.2 fish/hr and were collected at eleven different trawl sites. Average length of YOY tullibee in the trawls was 2.85 inches. Ten YOY walleye were caught while trawling and their average length was 3.92 inches.
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\n
\nInvasive Species
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\nZebra mussel density appears to have stabilized over the last three years, where it has averaged about 1050/ft2. Veliger (larval zebra mussels) densities decreased in 2014 and were the lowest observed since 2009. Peak veliger densities for 2014 occurred in late June.
\n
\nSpiny water flea (Bythotrephes) was observed during each sampling period from May through September. Peak density occurred in September and was 2.6 Bythotrephes per sample, which was the lowest observed since spiny water flea was first observed in the fall of 2009. Cursory spot checks of fish stomachs show that age 1+ tullibee and age 1+ yellow perch are consuming spiny water flea.
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\nIt appears that spiny water flea have taken a toll on zooplankton numbers and biomass. Native zooplankton are a vital dietary staple for many larval and juvenile fish in Mille Lacs. We have been observing severe declines in various species that belong to three broad functional groups. Currently, all three groups show a severe level of depletion, but small cladocerans and large cladocerans show the greatest decrease, where throughout the summer they are now barely detectable in the samples.
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\n
\nMuskellunge Assessment
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\nAdult muskellunge were sampled during one week of the spring spawning run, with net sets occurring from 18 May through 22 May. In this five day period, 245 muskellunge were captured in 140 large frame trap net sets (1.75 muskellunge/net), mainly in the southern half of the lake. Twenty of the 245 fish were recaptures from a previous day, making a total of 225 individual fish sampled. 141 muskellunge were mature males, which ranged in length from 34.9 inches to 46.5 inches, with an average length of 42.1 inches. The remaining 104 muskellunge were mature females that ranged in length from 37.8 inches to 55.7 inches and had an average length of 49.6 inches. About 25% of the fish were greater than 50 inches in length. A Chapman modified Petersen mark-recapture population estimate utilizing marked fish from the 2013 spawning run estimated a population of adult muskellunge at about 1,920 individuals (� 870).
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Standard double frame, ¾ inch mesh trap nets were used to evaluate the local size structure of spawn-time Northern Pike in Hazelglade Bay. Netting began on 17 April, 2019 once surface ice had melted enough to allow the setting of nets and continued through 1 May when spawning appeared to be complete.
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\n138 individual Northern Pike were sampled, with 63 fish identified as female, 73 as male, one with sex not identified, and one immature fish with sex not identified. Females ranged in size from 24 inches to 42.5 inches in length, while male lengths ranged from 8.2 inches to 32.8 inches. A comparison of Northern Pike from the spring trap nets to fish observed in the previous fall's annual gill net sampling showed the trap net length frequency distribution covering a wider range of lengths than the gill nets, particularly at lengths below 18 inches. Although relatively few in number, the trap nets did capture smaller Northern Pike that would be of a size consistent with 2018 year class fish while the fall gill nets did not, possibly in part due to the lower sample size of fish observed in the 2018 fall gill nets (n = 48). The modes between the two gears were slightly offset at 23 inches to 25 inches in the spring trap nets and from 25 to 26 inches in the gill nets that were set the previous fall; however, the two distributions were statistically indistinguishable and showed a similar median length around 25.5 inches.
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\nWhile the current fall gill net index suggests a Northern Pike population that's below median level in abundance, the trap net sampling associated with the local Hazelglade population indicates that the size quality that Mille Lacs is known for, continues to remain intact. New regulations for Northern Pike that are specific to Mille Lacs will take effect the spring of 2020 and will no longer change between the winter and summer fishing seasons. The new regulation reduces the bag limit to three fish in possession, with a 30 inch maximum size limit. This new regulation should continue to maintain Mille Lacs' quality Northern Pike size structure.
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Walleye is the fish of interest to the majority of anglers that visit Mille Lacs Lake. After a series of weak year classes from 2009 through 2012, we have seen good natural reproduction of walleye since then. Of particular note is the 2013-year class, which is the third strongest year class produced since annual sampling began in 1979. With the restrictive regulations that have been in place in recent years, walleye from this year class have survived very well, and will be a large portion of what anglers catch. These walleye currently range from about 17 to almost 22 inches in length. The 2017-year class is also strong. Anglers will notice a fair abundance of these walleye, which average about 13 inches in length. In addition to these fish, good numbers of older, larger walleye are also present. The oldest walleye sampled last fall was a 23-year old female that was about 27 inches long.
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\nAnglers experienced very high catch rates of walleye through the summer of 2019 and the following winter. These high catch rates were the result of the low abundance of prey species (primarily small yellow perch). We anticipate that these high catch rates will continue into the early part of the summer.
\n
\nThe next most popular species on the lake is smallmouth bass. Few anglers choose to harvest a smallmouth bass, but the opportunity to catch a trophy-size individual is what draws anglers to the lake. Smallmouth bass sampling last spring indicated a very high quality population, with fish from 16 to 20-inches forming the bulk of the sample. Several individuals over 21-inches long were sampled.
\n
\nRelatively few anglers target northern pike, but the lake does support a high quality population of these fish. Sampling consistently documents individuals of over 40-inches in length. Muskellunge are also popular. Muskellunge are the only species that is routinely stocked in Mille Lacs Lake. Reports of muskellunge in the 60-inch class have been received from anglers and through sampling.
\n
\nAnglers have to be aware of several special regulations on Mille Lacs Lake. In order to stay within the State's allocation of the safe harvest level for walleye, fishing for walleye will be catch-and-release for most of the summer, except July. The walleye season will be closed in July. This means you may not fish specifically for walleye during the closure. In addition to the closure, you may not use many types of bait commonly used when fishing for walleye. With implementing the planned closure we hope to prevent an unplanned closure later in the summer, and thereby keep walleye fishing open through the fall.
\n
\nNew regulations for smallmouth bass and northern pike have also been put into place beginning this spring. Both of these regulations are designed to maintain the high quality of the smallmouth bass and northern pike populations. The smallmouth bass regulation has been changed from a 17 to 21-inch protected slot to a 17-inch maximum size. Similarly, the northern pike regulation is now a 30-inch maximum size, changed from a 30 to 40-inch protected slot, combined with a reduction in possession from 5 to 3 northern pike. The northern pike regulation will apply to the entire open season, rather than having a separate regulation during the winter.
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\nFinally, Mille Lacs Lake has been designated an infested water for a number of species. Make sure you drain, clean and dry your boat when you leave any water body to prevent spreading aquatic invasive species.
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Sampling Programs
\nMille Lacs Lake is one of ten lakes in Minnesota's Large Lake Program. These lakes have annual sampling of the fish populations, and frequent creel surveys. Specific to Mille Lacs Lake, sampling programs focusing on Walleye, Yellow Perch, Smallmouth Bass, and Northern Pike are conducted annually. Additionally, we have annual summer and winter creel surveys to document angler use and fish harvest.
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\nWalleye
\nWalleye management on Mille Lacs Lake is conducted cooperatively with the eight Tribes signatory to the Treaty of 1837. A safe harvest level for Walleye is determined annually and is based on information collected through various sampling programs. For the 2024 fishing year (December 2024 through November 2025) the safe harvest level was set at 201,600 pounds, which is a 28% increase from 2024 and is based on a similar percentage of increase in the lake's fishable Walleye biomass over the same time period. The boost in Walleye biomass occurred, in part, to a new age-class of fish recruiting into the harvestable stock; however, most of the increase in new biomass occurred due to plentiful forage aiding in a significant improvement in fish condition (plumpness) across all size ranges of Walleye. The 2025 State fishery portion of the safe harvest level is 113,600 pounds. By agreement, neither the Tribal nor State fishery harvest may exceed their respective quota. Fishing regulations are selected that offer the maximum opportunity to participate in the fishery (minimize likelihood of closures) and to offer opportunity to harvest, when possible, while staying within the quota. Because we were observing relatively low 2025 winter Walleye catch rates along with the increase in fall 2024 fish condition, regulations were liberalized for the 2025 open-water season to a two fish bag limit, with a minimum size of 17 inches, with only one fish over 20 inches.
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\nOur fall 2024 forage gill net assessment confirmed a high abundance of age-0 Yellow Perch and age-0 Tullibee. Both are suitable forage prey for Mille Lacs Walleye, although previous diet studies have indicated a preference for the age-0 Yellow Perch, if available. Age-0 Yellow Perch levels in the fall of 2024 were near the highest observed and during mid-summer of 2024 we began observing angler Walleye catch rates decreasing from the relatively high catch rates that occurred earlier in May and June. It is common to observe Walleye catch rates decrease in July due to new forage that becomes large enough for Walleye to easily find and consume. Walleye catch rates continued declining to the lowest ever observed during the winter of 2024-2025. Winter Walleye catch rates are highly correlated to catch rates observed the following spring, therefore, the decreased winter catch rates suggest that 2025 spring fishing for Walleye is also likely to be low.
\n
\nAnglers should expect to catch Walleye ranging in size from 13 to 25-inches long due to near median (or better) numbers of fish from all year classes, with the exception of the 2023 and 2018 year-classes. Anglers are likely to see large numbers of smaller 6-10 inch Walleye in their catch from the 2024-year class, which were sampled in the fall at a level near the highest observed. This year class was commonly reported as being caught by winter anglers, in part, due to their high abundance, but also because they are the first age class of Walleye to run low on forage due to gape limitations restricting the abundance of prey that can be readily consumed. Fall electrofishing and fine-mesh forage gill net sampling indicated that 2024 median age-0 Walleye length was relatively normal for the fall; however, we observed an extremely wide range of sizes from around three inches to over nine inches in length. In fact, 2024 had the largest age-0 Walleyes ever measured in our annual sampling, which was due to an early spring (March 16 ice-out) providing an extra month of growing season, along with abundant forage.
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\nYellow Perch
\nYellow Perch from the 2018 through 2023-year classes were sampled near or well above median in the fall survey nets with particularly strong numbers of 9-to-12-inch fish from the 2021 year-class. These larger sized fish have been available for several years; however, catch rates had remained relatively weak overall, until the winter of 2025, where anglers had good ice conditions and were able to harvest fish from the deeper offshore areas of the lake. In fact, the 2025 winter harvest of Yellow Perch was the highest observed since 2011. The winter Yellow Perch harvest in 2025 exceeded the state's annual quota, which prompted a more conservative regulation change to a five fish bag limit that will remain in place through November. We expect additional fish from the 2022 and 2023 year-classes to continue to grow into the fishable stocks over summer and to help continue to provide fish for harvest.
\n
\nSmallmouth Bass
\nSmallmouth Bass are managed to provide a high-quality fishery, and they are the second most common fish species that anglers pursue on Mille Lacs Lake. Current Mille Lacs regulations require anglers to release Smallmouth Bass longer than 17-inches. Spawning Smallmouth Bass are usually sampled during late May/early June using electrofishing gear. This is a sampling technique that allows fish to be released unharmed after they have their length measured. Smallmouth Bass were sampled from 9 May through 29 May in 2024 and ranged in length from 10.7 inches to 21.6 inches. Most fish were between 13 and 20 inches and showed no distinct mode, presenting an impressive balance in length that indicates new fish that are available to recruit to quality size and older fish that compose a large trophy component that attracts anglers from across the country. Smallmouth Bass are also sampled in the annual fall gill nets, which are set in the latter half of September. Although the gill nets are not particularly efficient at sampling bass over 15 inches, we did observe several fish from 16 to just under 21 inches, indicating that we continue to maintain a high-quality population that appears to be still increasing in Mille Lacs.
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\nNorthern Pike and Muskellunge
\nLike Smallmouth Bass, Northern Pike are managed to provide a high-quality fishery. Pike are managed with a 30-inch maximum size limit. Northern Pike are sampled in the spring, during spawning, using trap nets. Sampling fish with trap nets allows us to release the fish unharmed after we collect length and sex. We have found that very few male pike grow longer than 30-inches, while females will grow to be longer than 40-inches, with the largest just over 45 inches. Of the 605 fish sampled in 2024 the largest male was just over 35 inches and the largest female was 45.5 inches. About 20% of the fish we sampled were over 30-inches long, and 1% were trophy sized at over 40-inches in length.
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\nMuskellunge are periodically sampled about every five years to evaluate the quality of the adults. Our sample size was relatively low in our 2024 sampling, where we were able to examine 52 fish and was likely adversely affected by cooler temperatures that protracted the sampling period and failed to concentrate the adult fish in their typical spawning areas. Lengths ranged from 33.9 inches to 54.9 inches with the modal catch at around 45 inches. Further, 13.5% of the fish were over 50 inches. Despite the quality of Muskellunge available in Mille Lacs, anglers tend to fish the lake less than in the past; mainly due to low catch rates from a relatively low population of fish. In order to boost catch rates, beginning in the fall of 2025 eight hundred yearlings, if available, are proposed to be stocked annually. Yearling Muskellunge have at a minimum, a stocking equivalent to fingerlings of 1:5, which should improve population abundance both through the annual yearling stocking when compared to the past stocking of 3,000 fingerlings every other year along with the improved survival realized by stocking yearling fish. In addition to stocked fish, we have been able to genetically confirm successful reproduction of Muskellunge in Mille Lacs. In order to better evaluate the ratio of stocked fish to naturally reproduced fish in the lake, all stocked fish will be implanted with PIT (passive integrated transponder) tags to differentiate the two groups in future sampling events.
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\nZebra Mussels, Rusty Crayfish, and Zooplankton
\nZebra mussels were first observed in Mille Lacs in 2005. Peak density occurred in 2012 after which abundance began decreasing. By 2017, densities had declined to about one half of their peak abundance, and for the last few years abundance has been at about a quarter to a third of their peak. Zooplankton abundance had appeared to be slowly increasing the last several years; however, in 2022 we again saw densities begin to decrease. Rusty crayfish eDNA from water samples taken in 2021 indicated that this aquatic invasive species was now in Mille Lacs. Visual confirmation occurred that same year when two specimens were observed near the Father Hennepin State Park swimming beach. In 2023 we observed our first specimen in DNR sampling gear (standard fall gill nets) in the southwest quadrant of the lake and continued to observe relatively low numbers in the 2024 sampling. Our population of Rusty Crayfish appears to still be relatively small; however, as the population continues to increase, we may see aquatic plant beds consumed throughout the lake by this invasive crustacean.
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Walleye entered the winter of 2001-2002 in relatively poor condition caused primarily by a very poor 2001 yellow perch year class. Winter angling for walleye was excellent as a result of the lack of forage. The lack of forage and related low condition in walleye was still evident in May and June. This translated into some fantastic fishing, in which anglers caught approximately 4 million lbs of walleye. This was about four times greater than the previous high of about one million pounds in both 1992 and 2001. However, a very strong and fast growing yellow perch year class has emerged, and by the time of fall gill netting, condition had returned to near normal levels. The response to the yellow perch year class was evident to anglers as catch rates plummeted towards the end of July and continued low into the fall. Despite having a very narrow harvest slot of 14-16 inches, the walleye kill was 382,000 pounds. Of the total kill, harvest was 154,000 lb, and the remainder was estimated hooking mortality of released fish.Walleye year classes since 1991 have been more or less average. This steady recruitment has led to an increase in numbers of older, larger fish in the gill nets. The proportion of fish over 20 inches has been increasing steadily since 1995, and rose to 43% in 2002. The proportion this year was boosted by poor survival of the 2000 and 2001 year classes over the last 12 months. Both of these year classes were well represented in 2001. However, poor condition going into last winter and a probable increase in cannibalism apparently increased the mortality of the younger walleye.Numbers of adult yellow perch declined to 1980?s levels as the very large 1996 year class continued to grow older and diminish. Recruitment since 1996 has been spotty until 2002. The 2002 year class was abundant in both trawls and electrofishing, and YOY yellow perch were the largest ever observed, with some individuals exceeding 4 inches. Unlike the perch, tullibee numbers continued to plummet, while average size approached one pound. The low numbers of small and medium fish suggest that recruitment is unable to keep up with mortality, or that predation on tullibee was excessive during the absence of yellow perch. Burbot numbers have also been low for the last five years. Both of these species are on the edge of their ranges, and some recent years of long, warm summers may be stressing these coldwater species.Angler catches of northern pike and muskellunge were lower in 2002 than in 2001. This was somewhat surprising considering the low densities of forage for walleye. These species probably can more easily find alternate prey, such as larger perch, tullibee, and suckers, so that their vulnerability to anglers did not increase. Reports of large muskellunge continue to rise. High water levels early in the season created erosion problems in many areas around the lake. Rip rap was added by land owners and public agencies to protect roads, buildings, and property.
","surveyDate":"2002-09-17","lengths":{},"fishCatchSummaries":[],"headerInfo":{"wb_id":"48000200","survey_type":"Population Assessment","county":"Mille Lacs","survey_id":"113676","wb_name":"Mille Lacs","wb_type":"Lake","id_date":"2002-09-17","wb_alt_name":""},"surveyID":"113676","surveyType":"Standard Survey"},{"lengths":{},"fishCatchSummaries":[{"CPUE":"10.94","totalWeight":160.7,"gearCount":32,"averageWeight":"0.46","quartileCount":"4.9-17.6","quartileWeight":"0.4-0.5","gear":"Standard gill nets","species":"TLC","totalCatch":350},{"species":"BUB","totalCatch":26,"gear":"Standard gill nets","quartileCount":"0.0-0.2","averageWeight":"0.95","quartileWeight":"1.1-2.1","CPUE":"0.81","totalWeight":24.7,"gearCount":32},{"quartileWeight":"2.4-4.3","quartileCount":"0.9-4.3","averageWeight":"6.47","totalWeight":245.7,"gearCount":32,"CPUE":"1.19","totalCatch":38,"species":"NOP","gear":"Standard gill nets"},{"gear":"Standard gill nets","species":"BLC","totalCatch":17,"CPUE":"0.53","totalWeight":6.3,"gearCount":32,"quartileCount":"0.1-0.7","averageWeight":"0.37","quartileWeight":"0.2-0.5"},{"gear":"Standard gill nets","species":"WTS","totalCatch":25,"CPUE":"0.78","gearCount":32,"totalWeight":50.9,"averageWeight":"2.04","quartileCount":"0.8-2.4","quartileWeight":"1.6-2.1"},{"gear":"Standard gill nets","totalCatch":3,"species":"MUE","totalWeight":14.4,"gearCount":32,"CPUE":"0.09","quartileWeight":"3.3-8.0","quartileCount":"0.0-0.1","averageWeight":"4.80"},{"averageWeight":"1.75","quartileCount":"3.3-14.8","quartileWeight":"0.9-1.5","CPUE":"15.88","gearCount":32,"totalWeight":888,"species":"WAE","totalCatch":508,"gear":"Standard gill nets"},{"gear":"Standard gill nets","species":"SMB","totalCatch":1,"CPUE":"0.03","totalWeight":0.1,"gearCount":32,"quartileCount":"0.0-0.2","averageWeight":"0.10","quartileWeight":"0.8-1.5"},{"quartileCount":"0.0-2.3","averageWeight":"10.75","quartileWeight":"2.3-10.8","CPUE":"0.06","gearCount":32,"totalWeight":21.5,"species":"CAP","totalCatch":2,"gear":"Standard gill nets"},{"totalCatch":10,"species":"BLH","gear":"Standard gill nets","quartileWeight":"N/A","averageWeight":"0.52","quartileCount":"N/A","gearCount":32,"totalWeight":5.2,"CPUE":"0.31"},{"quartileWeight":"0.2-0.3","quartileCount":"9.9-57.1","averageWeight":"0.35","totalWeight":239.1,"gearCount":32,"CPUE":"21.38","totalCatch":684,"species":"YEP","gear":"Standard gill nets"},{"gear":"Standard gill nets","totalCatch":1,"species":"LMB","gearCount":32,"totalWeight":0.1,"CPUE":"0.03","quartileWeight":"0.2-1.0","averageWeight":"0.10","quartileCount":"0.0-0.1"},{"CPUE":"0.41","gearCount":32,"totalWeight":9.2,"quartileCount":"0.1-1.1","averageWeight":"0.71","quartileWeight":"0.3-0.6","gear":"Standard gill nets","species":"RKB","totalCatch":13}],"surveyDate":"1988-04-01","surveyID":"113265","surveyType":"Standard Survey","headerInfo":{"wb_type":"Lake","wb_name":"Mille Lacs","wb_alt_name":"","id_date":"1988-04-01","wb_id":"48000200","survey_type":"Population Assessment","county":"Mille Lacs","survey_id":"113265"},"narrative":"CREEL CENSUS DATA: TOTAL 1988 OPEN WATER SEASON FISHING PRESSURE WAS ESTIMATED AT 1,987,556 ANGLER HOURS. AN ESTIMATED 427,775 WAS WEIGHING 572,889 LBS. WERE HARVESTED. HARVESTS OF NORTHERN PIKE AND YELLOW PERCH WERE 4,506, AND 57,962. THE MEAN WEIGHT OF A WALLEYE, NORTHERN PIKE AND YELLOW PERCH HARVESTED WAS 1.34, 5.35 AND 0.57 LBS. RE- SPECTIVELY. THE SEASON CATCH FOR WALLEYE WAS 0.22 PER ANGLER HOUR. THE 1984 YEAR CLASS DOMINATED THE ANGLERS WALLEYE CATCH IN 1988. AT PRESENT THE LAKES WALLEYE POPULATION IS DOMIN- ATED BY THE 1984 YEAR CLASS. THERE IS ALSO AN ABUNDANCE OF LARGER WALLEYE PRESENT COMPRISED MOSTLY BY THE 1979 AND 1982 YEAR CLASSES. THE 1988 TRAWLING INDICATED A POTENTIALLY STRONG 1988 AND A MODERATELY STRONG 1987 WALLEYE YEAR CLASS. THE NORTHERN PIKE ABUNDANCE APPEARS TO BE STABLE WITH LITTLE VARIATION IN ABUNDANCE IN RECENT YEARS ADULT YELLOW PERCH ABUNDANCE WAS HIGH AND ABOVE MEAN CATCHES OBSERVED SINCE 1972. THE TULLIBEE CATCH WAS DOWN FROM THE HIGH CATCHES OBSERVED IN RECENT YEARS.
","surveySubType":"Population Assessment"},{"surveySubType":"Large Lake Survey","narrative":"RESULTS
\n
\nGill Nets
\n
\nWalleye catch per effort (CPE) in the inshore gillnets was 13.1 fish/net and 23.4 lb/net, with an average weight of 1.8 lb. In offshore nets, walleye CPE was 22.1 fish/net and 35.6 lb/net, and walleye averaged 1.6 lb. The CPE of walleye longer than 20 inches has shown a general decline since about 2002. The 2002, 2007 and 2008 year classes were the strongest in the gill nets.
\n
\nWalleye growth was well below average. Condition was about 3% below average for walleye less than 14 in, average for walleye from 14 to 20 in, and 2% above average for walleye over 20 in. The proportion of mature walleyes in the gill nets that were male was 42%. The declining proportion of males was related to a temporary increase in females from 1997 to 2003, concurrent with a gradual decrease in males.
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\nYellow perch CPE in the inshore gillnets was 93.4 fish/net and 16.6 lb/net. In the offshore nets, CPE was 58.3 fish/net and 12.0 lb/net. Growth rates for age 2 through 5 yellow perch were below average in 2009. The 2005 and 2006 year classes appeared average, and the 2007 year class of perch was very strong.
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\nTullibee CPE set new record highs with 34.8 fish/net and 10.0 lb/net in the inshore nets and 53.6 fish/net and 19.0 lb/net in the offshore nets. The high catches were due to the recruitment of a huge year class of age 1 fish. Unusually high numbers of YOY tullibee were also sampled in the gill nets. The average length of tullibee has been increasing since 2001. At the same time, tullibee in Mille Lacs Lake have been maturing earlier, with almost 80% of age 1 females bearing eggs in 2009.
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\nNorthern pike CPE in the inshore gill nets was 2.0 per lift . The average weight of northern pike was 4.7 lbs. Inshore nets sampled 9 different year classes, with most fish either age 1 or age 2. The catch rate for age 1 northern pike was the highest observed for the second consecutive year, suggesting strong recruitment in recent years.
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\nPike nets sampled 159 northern pike, or 9.9 pike/net. Mean weight of northern pike in the pike nets was 4.8 lb. Pike nets sampled 11 year classes of pike. Roughly equal numbers of pike were sampled from ages 1 through 4.
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\nOther species were also caught in standard gill nets, generally in low numbers. Some species, such as burbot and white sucker showed declining trends, although a pulse of young white suckers resulted in a substantial upswing in 2009. Catches of smallmouth bass and rock bass were both the highest observed in 2009.
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\n
\nTrawling
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\nTrawl CPE was 71.7/h for YOY walleye, 24.3/h for age 1 walleye, and 12.6/h for all older walleye. Catch rate for YOY walleye was 73% of the median, CPE for ages 1-4 were close to their respective medians, and catch for older walleye were well below the median. Few walleye over age 2 were sampled in the trawl in 2009. Average length of YOY walleye was low at 4.6 in.
\n
\nYellow perch CPE was 8,923/h for YOY and 508/h for older fish, most of which were age 1. Average length of YOY yellow perch was 2.3 in, which is toward the lower end of fall lengths for YOY perch. The arithmetic mean of YOY perch was the second highest recorded. Examination of historical data suggested that the geometric mean is a better measure of central tendency than an arithmetic mean for YOY perch. Based on geometric means, the 2009 average catch rate of 359 YOY perch per hour is about 30% higher than the long-term median.
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\n
\nElectrofishing
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\nElectrofishing catch rates for YOY walleye ranged from 10.0/mi at Wealthwood to 127.8/mi at St. Alban's Bay. Overall CPE for YOY walleye was 70.5/mi. Catch rates for age 1 walleye ranged from 8.6/mi at Hennepin to 105.0/mi at Wealthwood, with an average CPE of 40.4/mi. Catch rates for YOY walleye were close to average, while catch rates for age 1 walleye were the highest observed.
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\n
\nSpring Muskellunge Sampling
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\nSpring trapnetting collected 363 muskellunge, of which 27 were recaptures within the same year. The average length was 42.2 in, and 38 muskellunge (11%) were longer than 50 inches. The longest observed was 54.7 in.
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\nMuskellunge were aged by scales. As in previous years, ages 8 and above were found to be unreliable as many clipped fish were underaged. Naturally reproduced fish were confirmed from the 2002, 2003, and 2005 year classes (Ages 7, 6, and 4). Three unclipped age 1 fish were also likely to have been naturally reproduced. No unclipped fish were observed from the 2004 year class.
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\n
\nInvasive Species
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\nZebra mussel were counted along 15 transects. Zebra mussel density increased to 4.4/sq. ft., which was 55,000 times higher than in 2005. This year was the first year that anglers reported snagging small rocks with zebra mussels attached. A higher proportion of adult zebra mussels were found in 2009 than in the previous two years. Veliger densities were lower than in 2008, but similarly distributed across the season.
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\nSpiny water flea was found in Mille Lacs for the first time in 2009. A fisheries employee picked up spiny water fleas on his line while fishing in Mille Lacs Lake in September of 2009. This report expedited examinations of monthly zooplankton samples, in which two adult spiny water fleas were confirmed.
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\nDiscussion
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\nEffect of Cool Summers
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\nThe summers of 2008 and 2009 were relatively cool, and water temperatures in the lake remained cooler than normal. There were several effects on fish populations that can be attributed to the cool temperatures. First, growth rates of some species were reduced. Observed growth rates of juvenile and adult walleye in 2009 were very low, despite abundant small perch and tullibee for forage. Growth rates of adult yellow perch were also low. Young-of year perch and walleye in the trawl were both below average length. Second, tullibee growth was much faster than normally observed. In most years, YOY tullibee are too small to sample with gill nets, but in 2009 YOY was the second most abundant year class in the inshore gill nets. Third recruitment of some cool water species was greatly improved. Tullibee catches in gill nets were the highest observed, and consisted mostly of age 1 and YOY fish. White sucker numbers increased, mostly due to an increase in small suckers in the gill nets. Catches of age 1 northern pike were the highest recorded. Finally, hooking mortality on caught-and-released fish was lower.
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\nWalleye
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\nWalleye size structure has been affected by the size regulations that have been in place since 1997. The catch of walleye over 20 in initially increased, but has decreased in both inshore and offshore nets in recent years. While the numbers of walleye over 20 inches was near its peak, recruitment to age 3 or 4 was low, despite high numbers of YOY and age 1 walleye. As the numbers of larger walleye have come down, recruitment patterns seem to be improving. Improvement in this case is recognized by observing year-to-year changes in the length frequency of gill netted walleye. Pre-1997, the norm was for a year class to increase in abundance in the gill nets until age 3 or 4, and then gradually decrease. For reasons not well understood, the trend from 2003 through 2007 was to start with very strong age 0 abundances that diminished in the gill nets even in the first three years. In 2009, and to a lesser degree in 2008, changes in the size distribution in the gill nets were more similar to the pre-1997 pattern.
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\nSeveral indicators suggest a strong 2008 walleye year class. First, electrofishing catches for age 1 walleye were the highest observed. Second, catch rates for 2008 walleye in the inshore gill nets were very high. These walleye were small for their age, and so less vulnerable to the nets than age 1 walleye usually are, suggesting that the year class is stronger than gill nets suggested. There were also large numbers of YOY walleye caught in the forage nets in 2008, although the history for this gear is very short. However, catch rates in the trawl were about average. Also, many year classes since 2000 have started out looking very strong, only to end up moderately strong or average by age 5. As always, the ultimate determination of year class strength is several years away.
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\nThe absence of YOY walleye in the gill nets was unusual for recent assessments since numbers of YOY walleye have normally been well above average since 2000. The absence of young-of-year fish in the gill nets was probably the result of cool summer temperatures, which caused low growth rates for YOY walleye. The YOY walleye were simply too small for the gill nets. Lengths from trawling and electrofishing confirm the relatively small size of walleye in 2009.
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\nThe proportion of mature male walleyes has been declining since 1997. Changes that occurred at that time included the beginning of band gill netting, which harvests mostly male walleye, and protected slot regulations on anglers that reduced the kill of larger females. This type of change in relative mortality between the sexes is expected to alter the sex ratios. An increase in the number of females was evident in the gill nets from 1998 through 2003, while the abundance of males was fairly constant. Since 2003, catches of males and females have gone down in the gill nets, but the catch of males has gone down much faster. The number of mature females sampled has dropped to about 100 in the inshore gill nets, which is similar to pre-1997 levels. However, the number of mature males sampled has dropped from about 200 per year to about 70 per year. Perhaps the number of males will increase now that the numbers of females has come down, or perhaps males will need some protection in the future.
\nWalleye growth rates were low during 2009. This appears to have been primarily a function of the cool weather. Despite slower growth, larger walleye were able to attain good condition because of the abundance of forage, which consisted mostly of 2007 year class yellow perch, and 2008 and 2009 year classes of tullibee. Smaller walleye exhibited poor condition, which may be an indicator that the most abundant prey have become too large for smaller walleye, or that the density of small walleye was high enough to limit food availability through intra-specific competition. The relative lack of forage may result in good fishing for walleye less than 20 inches in 2010.
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\nYellow Perch
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\nThe data from individual trawl hauls within a year appeared to be approximately log-normally distributed. In the past, arithmetic means were used to compare forage abundance in the trawl. This was somewhat inappropriate because the data was not normally distributed. Therefore, the conclusion that the trawl CPE for YOY yellow perch was the second highest observed would be misleading. Another point to consider is that the Reddy Creek station, where the two very large catches occurred, was dropped in 2007 because of high numbers of Chinese mystery-snails, and was only sampled in 2009 to test if a trawl equipped with mud rollers would reduce the snail by-catch. If that station were not sampled, the catch of YOY perch would have been about 75% of average, rather than the second highest ever. The geometric mean in 2009 was about 30% above the long-term median, but much less than some recent year classes. The geometric mean is probably the best estimate of abundance to use, since it most appropriately deals with log-normally distributed data. The relatively low condition of smaller walleye would suggest that the ambiguity will only be resolved with time.
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\nNorthern Pike
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\nThis was the second consecutive year in which the inshore gillnet CPE for age 1 northern pike was the highest observed. Cool temperatures, high water levels, and the observed increase in larger females may all be contributing. Slot limits were applied to northern pike fishing in 1998, just a year before slots were applied to the walleye fishing. The response appeared to be similar. Numbers and biomass of mature female pike have been increasing in the inshore gill nets. Recruitment and/or survival of younger pike have also increased in the face of favorable environmental conditions.
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\nTullibee
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\nTullibee have benefitted from the cool summers of 2008 and 2009. Gill net catches were the highest ever observed in both inshore and offshore nets, with the majority of the catch being age 0 and age 1. Young-of-year tullibee were caught in numbers for the first time, which was an indicator of very fast growth in 2009. Also, the abundance of YOY tullibee in fine-mesh gill nets set in September were the highest observed in four years of forage netting. The high catches of YOY in the forage nets is probably a more reliable indicator of abundance than the low catches in the trawl. The high numbers of tullibee in the lake will increase the likelihood of an observable tullibee summer kill, especially if the summer should be warmer than average.
\nTullibee are an important part of the Mille Lacs food web. They will help maintain walleye growth rates and large maximum sizes, and may provide a buffer against cannibalism of small walleye by larger walleye. Many anglers have complained of a decrease in the numbers of very large walleye in Mille Lacs Lake, which was concurrent with the decrease in tullibee abundance. The large numbers of young tullibee that we are seeing now have contributed to the increase in condition of larger walleye, and may lead to higher growth and more very large walleye in the next few years. Larger forage items also contribute to faster growth in northern pike. The recent upswing in tullibee numbers is also believed to be the primary cause for poor muskellunge fishing in 2008 and 2009.
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\nThe average size-at-age of tullibee has also shown an increase over the last 10 years. This may be a simple density-dependent growth rate response resulting from more food for remaining tullibee, or it may be a behavioral response to lower abundance. Faster growth has been accompanied by earlier maturation in Mille Lacs Lake, where the percent of females mature at age 1 has increased from 8% in 1999 to 80% in 2009.
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\nAlthough catches of tullibee vary from year to year, they appear to vary differently in inshore and offshore areas. Inshore catches have been almost entirely age 1 tullibee since 2003. In several years, the inshore catch of age 1 tullibee exceeded the 1987-1997 median, but in subsequent years, those year classes were absent from the inshore gill nets. In the offshore gillnets, these same year classes demonstrated relatively good concordance from year to year. Variability in tullibee vulnerability to the different surveys may be influenced by environmental conditions that affect movement, geographic or vertical distribution, or possibly even mortality in different manners. Tullibee catch rates are poor measures to judge abundance from year to year, but probably provide a general picture over time. Tullibee numbers have probably declined, but perhaps not to the extent represented by changes in the inshore gill nets.
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\nThe high catches of tullibee have prompted some discussion about when the sport-netting season may re-open. Criteria exist for reestablishing the sport-netting season (MN DNR records). These criteria include two consecutive years of more than 15 tullibee per inshore gill net, at least two tullibee per net age 2 or older, and at least five year classes of spawners (age 2 and older) in the inshore gill net sample. The criteria to reopen sport netting for State anglers were not met in 2009. There were not enough fish age 2 and older, nor were there enough year classes age 2 and older.
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\nMuskellunge
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\nThe length-frequency of adult fish appeared to be distributed approximately normally between 30 and 55 inches. Most of the smaller fish were younger males, while the larger fish were females, with considerable overlap between the sexes. The largest fish was between 54 and 55 inches, as was the case in 2008. Anglers sometimes report larger fish, and it has been speculated that our gear may be limiting the size of the muskellunge that we can catch. Aitkin Area trap nets have rigid openings that will eventually limit the size of a fish that can enter. The space between the bars on the muskellunge trap nets is 7.5 inches. Based on measurements from mounted fish, head widths would not be expected to approach 7.5 inches until at least 64 inches. It does not appear that the gear is too small for the largest fish.
\nWeight-at-length of muskellunge was higher in the late 1990's when most of the largest fish were Wisconsin strain. The Wisconsin strain has subsequently been identified as two strains, termed the Iowa strain (stocked in 1984 and persisting very well in Mille Lacs Lake) and the Wisconsin strain (stocked in 1985-1987, and doing rather poorly in Mille Lacs Lake). Weights of Iowa and Wisconsin fish averaged 12% heavier than observed in 2009 for muskellunge in the 45-50 in range. However, higher maximum weights were observed in 2009 when the largest muskellunge were over 4 inches longer than observed in the 1990's. In 2008, most of the fish over 51 inches were Leech Lake strain, although some were Iowa strain. It appears at this time that Leech Lake strain muskellunge tend to reach longer lengths than the Iowa or Wisconsin strains, and subsequently reaching heavier weights, even though they appear to be a little less robust.
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\nGenetic information can also be used to identify the proportion of natural fish in a population. Although 2009 data is not yet available, data from 2008 is now available that was not included in the 2008 report. The proportion of natural fish in the population can be approximated as the proportion of hybrids strain fish in the entire sample divided by the proportion of hybrids in a subsample of fish known to be naturally produced. For the 2008 sample, the estimated contribution of natural fish was 42%.
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\nZebra Mussels
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\nThe discovery of zebra mussels in Mille Lacs Lake in 2005 represents a potentially serious threat to Mille Lacs Lake and many others lakes to which zebra mussels from Mille Lacs Lake could be transported. The 2009 size distribution of zebra mussels observed while diving had more adults larger than 15 mm and fewer individuals less than 15 mm. This was due in part to the growth of small zebra mussels observed in 2007 and 2008, and apparently in part due to the cold water temperatures and poor growth of mussels that settled in the fall of 2008. Veliger counts were lower in 2009 than in 2008, which may also have been a result of cooler water temperatures.
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\nSpiny Water Flea
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\nThe discovery of spiny water flea adds one more layer of complexity to the bottom of the Mille Lacs food web. Spiny water fleas eat zooplankton, which is also eaten by young perch, walleye, and other species of fish. At the same time, zebra mussels will be consuming vast quantities of phytoplankton which supports the zooplankton. Hopefully the combination of new stressors to the zooplankton community will not result in changes to the fish communities.
\nThe addition of spiny water flea to the Mille Lacs community in the face of stricter regulations regarding the transportation of introduced species stresses the role that anglers and other boaters play in the control of introduced species. No matter how many laws and rules are put in place to slow the spread of new species, non-compliance by just a few people can result in new introductions that are potentially threatening to aquatic systems. The popularity of Mille Lacs Lake for fisherman not only makes the lake a likely place to receive new introductions, but also makes the lake a likely source of non-native species for introduction into other lakes all across Minnesota.
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Sampling Programs
\nMille Lacs Lake is one of ten lakes in Minnesota's Large Lake Program. These lakes have annual sampling of the fish populations, and frequent creel surveys. Specific to Mille Lacs Lake, sampling programs focusing on Walleye, Yellow Perch, Smallmouth Bass, and Northern Pike are conducted annually. Additionally, we have annual summer and winter creel surveys to document angler use and fish harvest.
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\nWalleye
\nWalleye management on Mille Lacs Lake is conducted cooperatively with the eight Tribes signatory to the Treaty of 1837. A safe harvest level for Walleye is determined annually and is based on information collected through various sampling programs. For the 2026 fishing year (December 2025 through November 2026) the state's allocation of the safe harvest level was set at 105,300 pounds, which is around a 7% decrease from 2025 and is based on a similar percentage of decrease in the lake's adult Walleye biomass over the same time period. The reduction in Walleye biomass occurred, in part, due to a weak age-class (2023) of fish recruiting into the fishable stock and a reduction in condition (plumpness) for medium sized (14\"-20\") Walleye due to reduced levels of forage for small and medium sized fish. By agreement, neither the Tribal nor State fishery harvest may exceed their respective quota. Fishing regulations are selected that offer the maximum opportunity to participate in the fishery (minimize likelihood of closures) and to offer opportunity to harvest, when possible, while staying within the quota. Despite the reduction in quota, summer Walleye regulations were actually liberalized because we were observing relatively low 2026 winter Walleye harvest rates. Regulations for the summer are a three fish bag limit, with a minimum size of 17 inches, with only one fish over 20 inches.
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\nDuring mid-summer of 2025 we began observing angler Walleye catch rates begin to increase. It is more common to observe Walleye catch rates decrease in July due to new forage that becomes large enough for Walleye to easily find and consume, so observing the opposite where catch rates are increasing is a strong indicator that new forage in the form of age-0 Yellow Perch is not available. Forage gill nets that were set in early September showed age-0 Yellow Perch levels in the fall of 2025 were the lowest observed. The same forage gill net assessment confirmed a high abundance of age-1 Yellow Perch and age-1 Tullibee. The age-1 fish are suitable forage prey for Mille Lacs Walleye over 20 inches, although previous diet studies have indicated a preference for the age-0 Yellow Perch, if available. Angler reports in the summer creel indicated that the majority of Walleye catch was from fish under 12 inches; another sign that age-0 forage was lacking and that larger Walleye were likely still feeding on age-1 Yellow Perch and Tullibee. Walleye catch rates continued increasing to the highest ever observed during the winter of 2025-2026; however, most of the catch again consisted of fish from the 2024 year-class that were under 13 inches. Winter Walleye catch rates are highly correlated to catch rates observed the following spring, therefore, the increased winter catch rates suggest that 2026 spring fishing for Walleye is also likely to be relatively high but will consist of mainly smaller fish.
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\nAnglers should expect to catch Walleye ranging in size from 6 to 28-inches long due to respectable numbers of fish from all year classes, with the exception of the 2023 cohort. Anglers are likely to see exceptional numbers of smaller 6-12 inch Walleye in their catch from the strong 2024-year class, which were sampled in the fall as at a level near the highest observed. This year class was commonly reported as being caught by winter anglers, in part, due to their high abundance, but also because they are the first age class of Walleye to run low on forage due to gape limitations restricting the abundance of prey that can be readily consumed. Fall electrofishing and fine-mesh forage gill net sampling indicated that 2024 median age-1 Walleye length was relatively small for the fall, due to the absence of forage. Harvestable sized fish in the 17-20 inch range will also likely become easier to catch earlier in the open-water season as the smallest 2024 year-class Yellow Perch continue to be cropped off as forage and as the remaining fish continue to grow beyond the gape limitations of moderate sized Walleye. We are unable to predict age-0 forage availability which typically becomes available in July. If the forage hatch is relatively normal, we would expect to see Walleye catches decline into the latter summer months; however, if new forage does not develop, we should see catch rates dramatically improve on the larger (>20\") Walleye and continue increasing on the smaller Walleye.
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\nYellow Perch
\nYellow Perch from the 2018 through 2024-year classes were sampled near or well above median in the fall survey nets with the age-1 fish being sampled at the highest ever recorded. Anglers begin to harvest Yellow Perch when they attain lengths over 9 inches. We've been sampling more of these larger sized fish since 2021; however, catch rates had remained relatively weak overall, until the winter of 2025, when anglers had good ice conditions and were able to harvest fish from the deeper offshore areas of the lake. In fact, the 2025 winter harvest of Yellow Perch was the highest observed since 2011. The winter Yellow Perch harvest in 2025 exceeded the state's annual quota, which prompted a more conservative regulation change to a five fish bag limit that will remain in place through November 2026. We expect additional fish from the 2022 through 2024 year-classes to continue to grow into the fishable stock over summer which should help continue providing fish for harvest.
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\nSmallmouth Bass
\nSmallmouth Bass are managed to provide a high-quality fishery, and they are the second most common fish species that anglers pursue on Mille Lacs Lake. Current Mille Lacs regulations require anglers to release Smallmouth Bass longer than 17-inches. Spawning Smallmouth Bass are usually sampled during late May/early June using electrofishing gear. This is a sampling technique that allows fish to be released unharmed after they have their length measured. Smallmouth Bass were sampled from 7 May through 30 May in 2025 and ranged in length from 3.5 inches to 22.2 inches. Most fish were between 13 and 20 inches and showed an indistinct mode at 19 inches, presenting an impressive balance in length that indicates new fish that are available to recruit to quality size and older fish that compose a large trophy component that attracts anglers from across the country. Smallmouth Bass are also sampled in the annual fall gill nets, which are set in the latter half of September. Although the gill nets are not particularly efficient at sampling bass over 15 inches, we did observe several fish from 16 to just under 21 inches, indicating that we continue to maintain a high-quality population that appears to be still increasing in Mille Lacs.
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\nNorthern Pike
\nLike Smallmouth Bass, Northern Pike are managed to provide a high-quality fishery. Pike are managed with a 30-inch maximum size limit. Northern Pike are sampled in the spring, during spawning, using trap nets. Sampling fish with trap nets allows us to release the fish unharmed after we collect length and sex. We have found that very few male pike grow longer than 30-inches, while females will grow to be longer than 40-inches, with the largest specimens growing to over 45 inches. Of the 259 fish sampled in 2025 the largest male was just under 33 inches, and the largest female was 41.5 inches. About 24% of the fish we sampled were over 30-inches long, and 2% were trophy sized at over 40-inches in length.
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\nZebra Mussels, Rusty Crayfish, and Zooplankton
\nZebra mussels were first observed in Mille Lacs in 2005. Peak density occurred in 2012 after which abundance began decreasing. By 2017, densities had declined to about one half of their peak abundance, and for the last several years abundance has been at about a quarter to a third of their peak.
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\nZooplankton abundance began dropping in 2010 but then showed increasing numbers from 2017 to 2021; however, in 2022 we again saw densities begin to decrease. While all functional groups of zooplankton have shown declines in abundance, small cladocerans, cyclopoids, and calanoids have shown the most acute decreases in density. These smaller sized zooplankton are important components in the food web, particularly for larval game fish as well as many of the smaller forage species. Much of the declines in zooplankton can be attributed to Zebra Mussels and Spiny Water Flea. Zebra Mussels remove mass quantities of phytoplankton (algae), which is the main food for smaller zooplankton. Spiny Water Flea are an active predator that preys directly on the smaller zooplankton and thus competes with larval and smaller fish for this food supply.
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\nRusty crayfish eDNA from water samples taken in 2021 indicated that this aquatic invasive species was now in Mille Lacs. Visual confirmation occurred that same year when two specimens were observed near the Father Hennepin State Park swimming beach. In 2023 we observed our first specimen in DNR sampling gear (standard fall gill nets) in the southwest quadrant of the lake and continued to observe relatively low numbers in the 2024 and 2025 fall sampling. A total of seven Rusty Crayfish were observed in the 2025 gill nets. Our population of Rusty Crayfish appears to still be relatively small; however, as the population continues to increase, we may see aquatic plant beds consumed throughout the lake by this invasive crustacean.
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SPECIAL PROBLEMS AND CONDITIONS AFFECTING FISH AND FISHING: AS IN 1995, WATER TRANSPARENCY WAS HIGH AND MAY HAVE RESULTED IN BELOW NORMAL ANGLER CATCH RATES DURING DAYLIGHT HOURS. NORMAL SUMMER SECCHI TRANSPARENCIES AVERAGE ABOUT 7 FEET, BUT IN JULY, 1996 THE AVERAGE WAS 17 FEET. ANGLERS APPEARED TO CHANGE THEIR PATTERNS BY FISHING LATER INTO THE EVENING AND IN DEEPER WATER. THE REASON FOR THE CLEAR WATER IS UNKNOWN.ADDITIONAL FIELD NOTES: CREEL SURVEY DATA: TOTAL 1996 OPEN WATER SEASON FISHING PRESSURE WAS ESTIMATED AT 1,903,488 ANGLER HOURS. AN ESTIMATED 333,758 WALLEYE WEIGHING 557,910 POUNDS WEREHARVESTED (4.21 LBS/SURFACE ACRE). THIS WAS THE THIRD HIGHEST HARVEST DOCUMENTED BY THE CREEL SURVEY. HARVESTS OF NORTHERN PIKE AND YELLOW PERCH WERE: 5,013 (24,157 LBS) AND 70,955 (31,019 LBS). THE MEAN WEIGHTS OF HARVESTED WALLEYE, NORTHERN PIKE, AND YELLOW PERCH WERE 1.67, 4.82, AND 0.44 POUNDS, RESPECTIVELY. THE SEASON HARVEST RATE FOR WALLEYE WAS 0.18 FISH PER ANGLER HOUR. THE 1993, 1992, 1991, AND 1988 YEAR CLASES WERE ABUNDANT IN THE ANGLERS CATCH, CREATING A RATHER WIDE LENGTH DISTRIBUTION FOR THE CATCH.PRESENT FISH POPULATION STATUS: WALLEYE ABUNDANCE (NUMBERS AND BIOMASS) AS INDICATED BY ASSESSMENT GILL NETTING WAS LOWER THAN IN 1995, AND SLIGHTLY BELOW AVERAGE. NO ONE YEAR CLASS ACCOUNTED FOR MORE THAN 20 PERCENT OF THE CATCH IN THE GILL NET SAMPLE. THE 1995, 1994, 1993, 1992, 1991, AND 1988 YEAR CLASSES CONTRIBUTED BETWEEN 10 AND 20 PERCENT. THE INDEX OF YEAR CLASS STRENGTH INDICATES NEAR AVERAGE RECRUITMENT FOR 1991 THROUGH 1994.SUMMARY BY SAMPLING METHOD:SPRING TRAP NETTING: BETWEEN APRIL 16 AND MAY 10, 1996 WE CAPTURED 3,978 NORTHERN PIKE OF WHICH 2,747 WERE TAGGED (INCLUDING 524 THAT WERE DOUBLE TAGGED TO ESTIMATE TAG LOSS). THERE WERE 258 RECAPTURES FROM THE 1994 AND 1995 TAGGINGS. PIKE WERE MORE ABUNDANT THAN IN PAST YEARS. THE SUM OF THE POPULATION ESTIMATES FOR EACH INDIVIDUAL TAGGING ZONE WAS 32,695, HIGHER THAN THE PAST 4 YEARS ESTIMATES (1992 - 14,735; 1993 - 12,829; 1994 - 24,874; 1995 - 14,785). RECRUITMENT FROM A STRONG 1993 YEAR CLASS WAS THE PRIMARY REASON FOR THE INCREAS IN NUMBERS. WE ALSO CAUGHT 305 MUSKELLUNGE (265 WERE TAGGED). TO DATE WE HAVE RECEIVED INFORMATION FROM ANGLERS WHO CAUGHT OVER 430 NORTHERN PIKE AND 3 MUSKELLUNGE TAGGED IN 1994, 1995, AND 1996.THE CATCH RATE DURING TH 1996 MUSKY ASSESSMENT WAS ABOUT 1.8/NET, WHICH WAS SIMILAR TO WHAT WAS OBSERVED IN 1994 (2/NET) AND 1995 (1.7/NET). THE NUMBER OF LARGE INDIVIDUALS CONTINUED TO INCREASE; ONE OF 250 IN 1992 WAS OVER 45\", SIX OF 163 IN 1993, 17 OF 256 IN 1994, 25 OF 205 IN 1995, AND 55 OF 305 IN 1996. THE LARGEST MUSKY WAS 49.1\" AND WEIGHED 40.5 POUNDS. WE ALSO CAPTURED 31 YEARLING MUSKELLUNGE, OF WHICH TWO WERE NATURALLY REPRODUCED (THEY WERE NOT FIN CLIPPED). EVIDENCE OF NATUAL REPRODUCTION OF MUSKELLUNGE IN MILLE LACS HAS BEEN DOCUMENTED EACH YEAR SINCE 1991.SUMMER SEINING: GROWTH OF YOY WALLEYE AND YOY YELLOW PERCH APPEARED ABOVE AVERAGE, ALTHOUGH THE NUMBERS OF WALLEYE SAMPLED WERE QUITE LOW.AUGUST NIGHT ELECTROFISHING AND FALL TRAWLING: THE TOTAL WALLEYE TRAWL CATCH WAS THE LOWEST SINCE 1975, AND YOY WALLEYE WERE CAUGHT AT THE THIRD LOWEST RATE THAT HAS BEEN OBSERVED SINCE THE TRAWL ASSESSMENT BEGAN IN 1972. THE EXTREMELY CLEAR WATER (10-12FT. SECCHI) LIKELY IMPACTED THE EFFICIENCY OF THE TRAWL. REGRESSION ANALYSIS INDICATED A SIGNIFICANT NEGATIVE RELATION BETWEEN WATER CLARITY AND TRAWL CATCH. SIZE WAS SIMILAR TO LAST YEAR (SLIGHTLY AVOVE AVERAGE). ELECTROFISHING RESULTS INDICATED THAT THE 1996 YEAR CLASS IS LIKELY BELOW AVERAGE IN ABUNDANCE, BUT NOT NEARLY AS POOR AS THE TRAWL CATCH WOULD SUGGEST. THE TRAWL CPUE OF YOY YELLOW PERCH WAS NEAR AVERAGE, AND THERE WAS NO MEASURABLE RELATION BETWEEN CLARITY AND YOY PERCH CATCH RATES.FALL GILL NETTING: WALLEYE CPUE (13.1/NET) WAS DOWN FROM LAST YEARS HIGH LEVEL; HOWEVER, THE NUMBER OF OLDER FISH (OVER AGE 8) IN THE SMPLE INCREASED TO THE HIGHEST LEVEL SINCE 1992. THE HIGHER CATCH OF OLDER FISH WAS DUE TO RECRUITMENT OF THE STRONG 1988 YEAR CLASS. YELLOW PERCH CPUE (78.1/NET) WAS DOWN FROM LAST YEAR BUT WAS STILL THE SECOND HIGHEST EVER RECORDED. THE STRONG 1993 YEAR CLASS (ABOUT 6.5-7.5 INCHES) ACCOUNTED FOR THE LARGEST PORTION OF THE CATCH. THE CATCH OF PERCH IN THE 8-9\" SIZE RANGE WAS ALSO UP, BUT THE NUMBER OF FISH OVER 10\" REMAINED ABOUT THE SAME AS LAST YEAR. NORTHERN PIKE CPUE (1.1/NET) WAS HIGHER THAN LAST YEAR AND WAS SUPPORTED BY THE INCREASE IN ABUNDANCE AS OBSERVED IN THE TAGGING EXPERIMENT.CREEL SURVEY: THE 1996 OPEN WATER ANGLING EFFORT (1,903,488 ANGLER HOURS), WALLEYE HARVEST (557,910 LBS), AND CATCH RATES (0.18/HOUR, 0.29 LBS/HOUR) WERE SIMILAR TO THE 1988 SEASON. ALTHOUGH THE HARVEST OF WALLEYE OVER 20 INCHES WAS NO DIFFERENT THAN IN 1988 (43,759 - 1996 VS 44,776 - 1988); THE TOTAL CATCH WAS THE HIGHEST OVSERVED (63,105), WITH A 31 PERCENT (19,346) RELEASE RATE. THE \"ONE OVER 20 INCHES\" SIZE REGULATION HAD A GREATER IMPACT IN 1996 THAN IN ANY OTHER YEAR SINCE ITS INCEPTION IN 1985. THE REGULATION ACCOUNTED FOR NEARLY HALF OF THE TOTAL RELEASES OF FISH OVER 20 INCHES (15 PERCENT OF THE TOTAL CATCH OVER 20 INCHES). YELLOW PERCH HARVEST REMAINED ABOUT THE SAME AS THE LAST SEVERAL YEARS (31,019 LBS), AS DID THE NUMBER OF PERCH RELEASED (279,235 FISH). NORTHER PIKE CATCH (11,724) AND HARVEST (5,013 FISH, 24,157 LBS) WERE ALSO UP FROM LAST YEAR. THE HIGH CATCH OF PIKE WAS DUE TOT THEIR INCREASED ABUNDANCE AND THE INCREASED EFFOT. MUSKELLUNGE ANGLERS AGAIN EXPERIENCED EXCELLENT ANGLING. THE TOTAL CATCH EXCEEDED THE PREVIOUS HIGHEST CATCH BY 200 FISH (1,059 RELEASED). NO HARVESTED MUSKELLUNGE WERE OBSERVED IN THE CREEL SURVEY. THE AVERAGE SIZE CAUGHT BY ANGLERS THAT WERE INTERVIEWED IN THE CREEL SURVEY WAS 36\" AND 32 PERCENT WERE OVER 40\". THE LARGEST FISH REPORTED RELEASED BY AN ANGLER IN THE CREEL WAS 46\". PRESSURE DIRECTED AT MUSKELLUNGE OR MUSKELLUNGE IN COMINATION WITH OTHER SPECIES CONTINUED TO INCREASE, DOUBLE THAT OF 1995 EFFORT. IN 1996, CREEL CLERKS SAMPLED 1,314 HOURS OF EFFORT COMPARED WITH 654 HOURS IN 1995, 536 HOURS IN 1994, 358 HOURS IN 1993 AND 202 HOURS IN 1992.
","surveySubType":"Population Assessment"},{"surveyType":"Standard Survey","surveyID":"113251","headerInfo":{"county":"Mille Lacs","survey_id":"113251","survey_type":"Population Assessment","wb_id":"48000200","wb_alt_name":"","id_date":"1987-09-01","wb_type":"Lake","wb_name":"Mille Lacs"},"lengths":{},"fishCatchSummaries":[{"quartileWeight":"1.1-2.1","averageWeight":"0.30","quartileCount":"0.0-0.2","gearCount":32,"totalWeight":0.3,"CPUE":"0.03","totalCatch":1,"species":"BUB","gear":"Standard gill nets"},{"gear":"Standard gill nets","species":"NOP","totalCatch":38,"CPUE":"1.19","gearCount":32,"totalWeight":215.2,"averageWeight":"5.66","quartileCount":"0.9-4.3","quartileWeight":"2.4-4.3"},{"gear":"Standard gill nets","totalCatch":15,"species":"RKB","gearCount":32,"totalWeight":6.6,"CPUE":"0.47","quartileWeight":"0.3-0.6","averageWeight":"0.44","quartileCount":"0.1-1.1"},{"gear":"Standard gill nets","totalCatch":506,"species":"WAE","gearCount":32,"totalWeight":1040,"CPUE":"15.81","quartileWeight":"0.9-1.5","averageWeight":"2.06","quartileCount":"3.3-14.8"},{"gear":"Standard gill nets","species":"YEP","totalCatch":564,"CPUE":"17.62","gearCount":32,"totalWeight":110.6,"averageWeight":"0.20","quartileCount":"9.9-57.1","quartileWeight":"0.2-0.3"},{"quartileWeight":"1.6-2.1","quartileCount":"0.8-2.4","averageWeight":"1.71","totalWeight":77,"gearCount":32,"CPUE":"1.41","totalCatch":45,"species":"WTS","gear":"Standard gill nets"},{"gearCount":32,"totalWeight":4,"CPUE":"0.03","quartileWeight":"3.3-8.0","quartileCount":"0.0-0.1","averageWeight":"4.00","gear":"Standard gill nets","totalCatch":1,"species":"MUE"},{"gear":"Standard gill nets","totalCatch":785,"species":"TLC","totalWeight":262.6,"gearCount":32,"CPUE":"24.53","quartileWeight":"0.4-0.5","quartileCount":"4.9-17.6","averageWeight":"0.33"}],"surveyDate":"1987-09-01","narrative":"AT PRESENT THE MILLE LACS LAKE WALLEYE POPULATION IS DOMINATED BY 1984, 1982 AND 1979 YEAR CLASS WALLEYE. THE 1984 YEAR CLASS OF WALLEYE STRONGLY ENTERED THE 1984 ANGLERS CATCH, AND WILL DOMINATE THE 1988 ANGLERS CATCH. THE 1979 AND 1982 YEAR CLASSES OF WALLEYE APPEAR TO BE IN GOOD ABUNDANCE FOR THEIR AGE. NORTHERN PIKE CATCH PER NET WAS LOWER THEN THE 1972-86 MEAN BUT WITHIN PAST OB- SERVED LEVELS. THE ADULT YELLOW PERCH CATCH RATE WAS SLIGHTLY ABOVE THE 1972-86 MEAN CATCH RATE. TULLIBEE CATCH RATE WAS HIGH, AND NEAR NORMAL HIGHS OBSERVED SINCE 1972.
","surveySubType":"Population Assessment"},{"narrative":"The walleye population appeared quite healthy in 2003. The gill net catch was the highest observed since 1995. Condition of the walleye returned to average, many year classes were represented in the spawning stock, and recruitment in recent years was certainly adequate. Weak 2000 and 2001 year classes were the result of the nearly absent 2001 yellow perch year class. This reduced the condition of the smaller walleye, and may have led to increased natural mortality. Additionally, the larger walleye were in very poor condition in 2001 and 2002. This led to increased levels of cannibalism and may have also weakened the year classes. The very strong 2002 and possibly strong 2003 yellow perch year classes alleviated both of these conditions, and the very strong 2002 and possibly strong 2003 walleye year classes are expected to persist. The abundant perch reduced angling success for walleye. Catch rates were low in both winter and summer, and fishing pressure reflected the lower than average fishing success for walleye. Despite a slight relaxation of walleye regulations, anglers harvest only 35,000 lbs of walleye for the 2003 angling year. Total kill, including hooking mortality estimates, was 66,500 lb.Although gill net catches have changed little over the last four years, the yellow perch population structure has changed dramatically. Poor recruitment since the 1996 year class culminated in almost no recruitment in 2001. However, the 2002 year class was very strong, and is growing rapidly; some age 1 perch exceeded 7.5 in this fall. This fast growth may be biasing the year class strength index upward by speeding recruitment to the sampling gear. Early indicators suggested that the 2003 year class of yellow perch was also strong and providing plenty of forage for the 2002 perch year class as well as young-of-the-year walleye. Heavy predation may ultimately reduce the strength of the 2003 yellow perch year class. Tullibee gill net CPE increased in both inshore and offshore nets. Much of the increase was in the form of age 1 fish. Despite these increases, angling success was the poorest observed. Poor recruitment during several warm falls and longer, warmer summers have been hypothesized as major contributing factors to the recent decline in tullibee in Mille Lacs Lake. Similar declines have been observed in Leech and Winnibigoshish lakes as well. Sport netting for tullibee was closed on Mille Lacs Lake after the 2002 gill net survey produced a tullibee CPE of less than one per net in the inshore gill nets. Muskellunge stocking was also curtailed at that time to maximize the likelihood of increasing tullibee CPE. The lack of older tullibee in the inshore nets suggested that conservative management practices remain prudent.
","surveySubType":"Population Assessment","surveyType":"Standard Survey","surveyID":"113708","headerInfo":{"wb_alt_name":"","id_date":"2003-09-14","wb_name":"Mille Lacs","wb_type":"Lake","survey_id":"113708","county":"Mille Lacs","wb_id":"48000200","survey_type":"Population Assessment"},"lengths":{},"fishCatchSummaries":[{"totalWeight":39.2,"gearCount":32,"CPUE":"5.56","quartileWeight":"0.4-0.5","quartileCount":"4.9-17.6","averageWeight":"0.22","gear":"Standard gill nets","totalCatch":178,"species":"TLC"},{"gearCount":32,"totalWeight":1.1,"CPUE":"0.03","quartileWeight":"1.1-2.1","quartileCount":"0.0-0.2","averageWeight":"1.10","gear":"Standard gill nets","totalCatch":1,"species":"BUB"},{"totalCatch":49,"species":"NOP","gear":"Standard gill nets","quartileWeight":"2.4-4.3","quartileCount":"0.9-4.3","averageWeight":"6.22","totalWeight":304.9,"gearCount":32,"CPUE":"1.53"},{"species":"BLC","totalCatch":5,"gear":"Standard gill nets","averageWeight":"0.18","quartileCount":"0.1-0.7","quartileWeight":"0.2-0.5","CPUE":"0.16","totalWeight":0.9,"gearCount":32},{"CPUE":"0.53","totalWeight":27,"gearCount":32,"averageWeight":"1.59","quartileCount":"0.8-2.4","quartileWeight":"1.6-2.1","gear":"Standard gill nets","species":"WTS","totalCatch":17},{"quartileWeight":"0.9-1.5","averageWeight":"2.02","quartileCount":"3.3-14.8","totalWeight":1035.2,"gearCount":32,"CPUE":"16.00","totalCatch":512,"species":"WAE","gear":"Standard gill nets"},{"quartileCount":"0.0-0.2","averageWeight":"2.80","quartileWeight":"0.8-1.5","CPUE":"0.03","totalWeight":2.8,"gearCount":32,"species":"SMB","totalCatch":1,"gear":"Standard gill nets"},{"totalWeight":0.6,"gearCount":32,"CPUE":"0.03","quartileWeight":"0.6-1.1","averageWeight":"0.60","quartileCount":"0.1-1.1","gear":"Standard gill nets","totalCatch":1,"species":"YEB"},{"quartileWeight":"N/A","averageWeight":"0.30","quartileCount":"N/A","totalWeight":0.6,"gearCount":32,"CPUE":"0.06","totalCatch":2,"species":"BLG","gear":"Standard gill nets"},{"totalWeight":356.5,"gearCount":32,"CPUE":"43.97","quartileWeight":"0.2-0.3","quartileCount":"9.9-57.1","averageWeight":"0.25","gear":"Standard gill nets","totalCatch":1407,"species":"YEP"},{"CPUE":"0.38","totalWeight":6.2,"gearCount":32,"quartileCount":"0.1-1.1","averageWeight":"0.52","quartileWeight":"0.3-0.6","gear":"Standard gill nets","species":"RKB","totalCatch":12}],"surveyDate":"2003-09-14"},{"surveySubType":"Population Assessment","narrative":"Based on gill net data, the walleye population in Mille Lacs was close to average in numbers. The 1991 through 1996 year classes are all close to average in strength, except for the 1994 year class that is somewhat weaker. The 1997 year class appeared weak, but the 1998 year class was strong, or at least very fast growing. Good growth in 1997 and 1998 has resulted in larger than average walleye from the 1994 through 1998 year classes. The yellow perch gill net catches continued to increase to the highest ever observed in Mille Lacs Lake. The increase appeared to be from a number of increasingly strong year classes, perhaps related directly or indirectly to water clarity. Good numbers of large fish are expected to provide excellent angling opportunities, and forage for northern pike and muskellunge. Smaller sizes will also provide a good forage base for walleye. Good recruitment from the 1993 and 1994 year classes of northern pike has increased their abundance, but exploitation should be monitored closely to prevent over-harvest. The new size limit for northern pike (26-36\" protected slot) should protect a large number of pike, which will allow more to grow to trophy sizes. The muskellunge population continued to grow in numbers and individual size. Natural reproduction is occurring and may have the potential to sustain the fishery on its own in future years without need for maintenance stocking. Muskellunge stocking will continue until the contribution of stocked muskellunge can be evaluated over the next several years. The Leech Lake strain, which replaced the Wisconsin strain in 1991, has the potential to grow to even larger sizes than observed so far in Mille Lacs Lake. There is a need for better smallmouth bass data in the face of pressure to apply special regulations to this species.
","surveyType":"Standard Survey","surveyID":"113608","headerInfo":{"wb_alt_name":"","id_date":"1998-09-07","wb_type":"Lake","wb_name":"Mille Lacs","county":"Mille Lacs","survey_id":"113608","survey_type":"Population Assessment","wb_id":"48000200"},"fishCatchSummaries":[{"gear":"Standard gill nets","species":"TLC","totalCatch":253,"CPUE":"7.91","gearCount":32,"totalWeight":70.4,"quartileCount":"4.9-17.6","averageWeight":"0.28","quartileWeight":"0.4-0.5"},{"CPUE":"0.16","totalWeight":5.1,"gearCount":32,"quartileCount":"0.0-0.2","averageWeight":"1.02","quartileWeight":"1.1-2.1","gear":"Standard gill nets","species":"BUB","totalCatch":5},{"quartileWeight":"2.4-4.3","averageWeight":"5.01","quartileCount":"0.9-4.3","totalWeight":195.2,"gearCount":32,"CPUE":"1.22","totalCatch":39,"species":"NOP","gear":"Standard gill nets"},{"quartileCount":"0.1-0.7","averageWeight":"0.24","quartileWeight":"0.2-0.5","CPUE":"0.31","gearCount":32,"totalWeight":2.44,"species":"BLC","totalCatch":10,"gear":"Standard gill nets"},{"gearCount":32,"totalWeight":56.3,"CPUE":"0.88","quartileWeight":"1.6-2.1","averageWeight":"2.01","quartileCount":"0.8-2.4","gear":"Standard gill nets","totalCatch":28,"species":"WTS"},{"quartileWeight":"0.9-1.5","quartileCount":"3.3-14.8","averageWeight":"2.13","totalWeight":985.6,"gearCount":32,"CPUE":"14.44","totalCatch":462,"species":"WAE","gear":"Standard gill nets"},{"totalCatch":1,"species":"PMK","gear":"Standard gill nets","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"0.20","totalWeight":0.2,"gearCount":32,"CPUE":"0.03"},{"averageWeight":"2.35","quartileCount":"0.0-2.3","quartileWeight":"2.3-10.8","CPUE":"0.03","gearCount":32,"totalWeight":2.35,"species":"CAP","totalCatch":1,"gear":"Standard gill nets"},{"gear":"Standard gill nets","totalCatch":85,"species":"BLH","totalWeight":19.8,"gearCount":32,"CPUE":"2.66","quartileWeight":"N/A","averageWeight":"0.23","quartileCount":"N/A"},{"totalCatch":7521,"species":"YEP","gear":"Standard gill nets","quartileWeight":"0.2-0.3","averageWeight":"0.19","quartileCount":"9.9-57.1","totalWeight":1407.9,"gearCount":32,"CPUE":"235.03"},{"quartileCount":"0.1-1.1","averageWeight":"0.60","quartileWeight":"0.3-0.6","CPUE":"1.81","totalWeight":34.9,"gearCount":32,"species":"RKB","totalCatch":58,"gear":"Standard gill nets"}],"lengths":{},"surveyDate":"1998-09-07"},{"narrative":"Mille Lacs Lake is one of the most popular walleye and perch fishing destinations in Minnesota. Anglers spent 2.8 million hours fishing Mille Lacs Lake in 2000. The walleye population appears healthy with an unbroken string of fair to good year classes since 1991. Walleye catches in assessment nets were about average in 2000, with many fish over 20 inches, many young fish (age 0 and 1), but fewer than average walleye from 15 to 20 inches. From an angler's perspective, the return of normal water clarity to Mille Lacs Lake has translated to better daytime fishing, which reduced the relative amount of night fishing considerably. The yellow perch population also appeared healthy based on 2000 sampling. Numbers of perch sampled were much lower in 2000 than in the previous two years, but still above average. The decrease since 1998 was due to the very large 1996 year class outgrowing the smaller mesh sizes. The 1996 year class was still well represented, and should be large enough to appeal to anglers for the next few years. Northern pike and muskellunge are not well sampled by standard methods in Mille Lacs Lake. The gill net catch of northern pike was about average at 1.1/net. Most of these fish were caught along the north shore. Anglers experienced above average catches for both northern pike and muskellunge. Anglers caught 23,000 pike in 2000, up from 15,000 in 1999. Pike numbers and sizes may be increasing as a result of the protected slot regulation on Mille Lacs Lake. Muskellunge catch was also higher this year, up to 2,500 during the 2000 season compared to 1,500 in 1999.
","surveySubType":"Population Assessment","headerInfo":{"survey_id":"113636","county":"Mille Lacs","wb_id":"48000200","survey_type":"Population Assessment","id_date":"2000-09-17","wb_alt_name":"","wb_name":"Mille Lacs","wb_type":"Lake"},"surveyID":"113636","surveyType":"Standard Survey","surveyDate":"2000-09-17","fishCatchSummaries":[{"species":"TLC","totalCatch":146,"gear":"Standard gill nets","averageWeight":"0.50","quartileCount":"4.9-17.6","quartileWeight":"0.4-0.5","CPUE":"4.56","gearCount":32,"totalWeight":72.49},{"gear":"Standard gill nets","totalCatch":6,"species":"BUB","totalWeight":8.4,"gearCount":32,"CPUE":"0.19","quartileWeight":"1.1-2.1","averageWeight":"1.40","quartileCount":"0.0-0.2"},{"quartileCount":"0.9-4.3","averageWeight":"5.90","quartileWeight":"2.4-4.3","CPUE":"1.09","totalWeight":206.64,"gearCount":32,"species":"NOP","totalCatch":35,"gear":"Standard gill 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nets","totalCatch":1,"species":"BRB","totalWeight":681,"gearCount":16,"CPUE":"0.06","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"1.50"},{"CPUE":"0.04","totalWeight":0,"gearCount":25,"quartileCount":"N/A","averageWeight":"0.00","quartileWeight":"N/A","gear":"Special gill nets","species":"SMB","totalCatch":1},{"gear":"Standard gill nets","species":"MUE","totalCatch":2,"CPUE":"0.04","totalWeight":13506,"gearCount":52,"averageWeight":"14.89","quartileCount":"0.0-0.1","quartileWeight":"3.3-8.0"},{"gear":"Standard gill nets","totalCatch":31,"species":"WTS","totalWeight":27556,"gearCount":52,"CPUE":"0.60","quartileWeight":"1.6-2.1","quartileCount":"0.8-2.4","averageWeight":"1.96"},{"totalCatch":1,"species":"MTS","gear":"Special electrofishing","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"0.00","gearCount":0.4,"totalWeight":0,"CPUE":"2.50"},{"quartileCount":"N/A","averageWeight":"3.26","quartileWeight":"N/A","CPUE":"15.94","gearCount":16,"totalWeight":377468,"species":"WAE","totalCatch":255,"gear":"Large-mesh gill nets"},{"species":"BLG","totalCatch":16,"gear":"Special electrofishing","averageWeight":"0.08","quartileCount":"N/A","quartileWeight":"N/A","CPUE":"40.00","totalWeight":608,"gearCount":0.4},{"quartileWeight":"N/A","averageWeight":"0.16","quartileCount":"N/A","gearCount":0.4,"totalWeight":72,"CPUE":"2.50","totalCatch":1,"species":"PMK","gear":"Special electrofishing"},{"quartileWeight":"N/A","averageWeight":"0.01","quartileCount":"N/A","gearCount":25,"totalWeight":118,"CPUE":"1.84","totalCatch":46,"species":"TRP","gear":"Special gill nets"},{"species":"BLC","totalCatch":1,"gear":"Special electrofishing","quartileCount":"N/A","averageWeight":"0.01","quartileWeight":"N/A","CPUE":"2.50","gearCount":0.4,"totalWeight":5},{"quartileWeight":"0.4-0.5","averageWeight":"1.18","quartileCount":"4.9-17.6","totalWeight":159016,"gearCount":52,"CPUE":"5.69","totalCatch":296,"species":"TLC","gear":"Standard gill nets"}],"lengths":{"TRP":{"fishCount":[[3,8],[4,5],[1,1],[2,32]],"maximum_length":4,"minimum_length":1},"NOP":{"minimum_length":18,"maximum_length":40,"fishCount":[[18,1],[19,3],[20,7],[21,9],[22,13],[23,17],[24,17],[25,31],[26,12],[27,14],[28,9],[29,6],[30,2],[31,1],[32,6],[33,2],[34,2],[35,4],[36,3],[37,1],[38,2],[39,1],[40,1]]},"YEP":{"fishCount":[[10,28],[11,29],[12,21],[13,2],[3,112],[4,251],[5,686],[6,164],[7,88],[8,60],[9,34],[1,5],[2,486],[3,44],[4,2]],"minimum_length":1,"maximum_length":13},"BNM":{"fishCount":[[2,1]],"maximum_length":2,"minimum_length":2},"YEB":{"minimum_length":10,"maximum_length":12,"fishCount":[[10,1],[12,1]]},"SMB":{"fishCount":[[10,2],[11,3],[12,10],[13,17],[14,7],[15,5],[16,12],[17,13],[18,10],[19,7],[21,1],[4,3],[5,2],[6,1],[7,1],[8,4],[9,1],[1,3],[2,14],[3,10],[4,2]],"minimum_length":1,"maximum_length":21},"RKB":{"maximum_length":11,"minimum_length":3,"fishCount":[[10,11],[11,5],[3,7],[4,5],[5,7],[6,5],[7,26],[8,9],[9,25]]},"BLC":{"fishCount":[[10,6],[2,1],[7,1],[8,2],[9,2]],"minimum_length":2,"maximum_length":10},"BOF":{"minimum_length":19,"maximum_length":28,"fishCount":[[19,1],[20,1],[21,2],[23,6],[24,3],[28,1]]},"TLC":{"fishCount":[[2,13],[3,12],[10,1],[11,10],[12,6],[13,32],[14,144],[15,81],[16,21],[17,5],[6,5],[7,23],[8,13]],"maximum_length":17,"minimum_length":2},"MUE":{"fishCount":[[19,1],[23,1],[24,1],[47,1]],"maximum_length":47,"minimum_length":19},"BUB":{"maximum_length":6,"minimum_length":6,"fishCount":[[6,1]]},"WAE":{"maximum_length":28,"minimum_length":2,"fishCount":[[2,1],[3,59],[4,142],[5,402],[6,393],[7,74],[10,72],[11,39],[12,11],[13,16],[14,50],[15,37],[16,65],[17,137],[18,158],[19,131],[20,95],[21,47],[22,34],[23,35],[24,42],[25,36],[26,25],[27,11],[28,1],[7,6],[8,28],[9,36]]},"SPO":{"maximum_length":4,"minimum_length":2,"fishCount":[[3,426],[4,69],[2,61],[3,1]]},"BRB":{"fishCount":[[13,1]],"maximum_length":13,"minimum_length":13},"LMB":{"minimum_length":2,"maximum_length":11,"fishCount":[[2,1],[4,1],[5,1],[11,1],[4,1],[5,2]]},"MTS":{"maximum_length":2,"minimum_length":2,"fishCount":[[2,1]]},"WTS":{"minimum_length":4,"maximum_length":25,"fishCount":[[4,2],[10,4],[11,1],[12,1],[13,1],[15,1],[16,5],[17,13],[18,13],[19,8],[20,8],[21,10],[22,3],[23,1],[25,1],[8,3],[9,1]]},"MMS":{"minimum_length":2,"maximum_length":2,"fishCount":[[2,1]]},"CAP":{"maximum_length":26,"minimum_length":26,"fishCount":[[26,1]]},"PMK":{"maximum_length":6,"minimum_length":5,"fishCount":[[5,1],[6,3]]},"BLG":{"maximum_length":8,"minimum_length":2,"fishCount":[[2,1],[3,4],[4,9],[5,4],[6,8],[7,13],[8,4]]},"LGP":{"minimum_length":3,"maximum_length":3,"fishCount":[[3,9]]}},"surveyDate":"2018-09-01","narrative":"The Mille Lacs Lake game fish community is primarily composed of Walleye, Yellow Perch, Northern Pike, Muskellunge, Tullibee, and Smallmouth Bass. Other game fish include Largemouth Bass, Bluegill, Pumpkinseed and Black Crappie. Common minnow species include Spottail Shiner and Mimic Shiner. Invasive animal species include Common Carp, Zebra Mussel, Chinese Mystery-snail, Banded Mystery-snail, and Spiny Water Flea. Curlyleaf Pondweed and Eurasian Watermilfoil are also well established in the lake.
\n
\nCreel Survey (December 1, 2017 to November 30, 2018)
\n
\nCreel survey is the tool through which we estimate angler use and harvest of various fish species on Mille Lacs Lake. Creel surveys have been conducted annually for both the summer and winter fisheries since 1983.
\n
\nFishing effort for the 2017-2018 winter season was 1,951,650 angler-hours (ang-hrs), about 11% above the 35 year average. An additional 23,000 angler-hours were observed during the late-ice creel. Winter ice fishing pressure tends to rise above average levels when good ice conditions are present. Open water fishing effort was approximately 615,350 ang-hrs, which remains about 53% below the 35 year average and is the fourth lowest observed. Summer Walleye anglers tend to react more negatively to conservative regulations and the catch-and-release regulations instituted over the last several open-water seasons have severely reduced summer angling pressure. Fishing effort from anglers targeting Smallmouth bass has helped to curtail some of the pressure lost from Walleye anglers, but overall effort remains reduced. Open water night effort was the lowest observed, due to an extended night closure that was in place through the open water season.
\n
\nWalleye harvest, for the entire 2018 fishing season, was the fourth lowest observed at around 5,500 lbs with harvest only allowed during winter under an 19\"-21\" harvest slot. Total summer and winter kill, which includes hooking mortality, was about 45,700 lbs. Walleye catch rates remained high in 2018 and anglers released close to a million pounds of Walleye.
\n
\nSmallmouth bass anglers again experienced strong catch rates on Mille Lacs and the total number of fish caught in 2018 was the third highest observed at approximately 125,500 fish. Harvest of Smallmouth remains relatively low with about 1,100 fish being kept by anglers, which is less than 1% of the total caught. 2018 targeted effort for Smallmouth Bass was the second highest observed and made up about 30% of the summer effort.
\n
\nFall Assessment
\nThe fall gill net sampling on Mille Lacs Lake is our most important tool for assessing the health and abundance of various fish populations in the lake. The survey has been conducted annually since 1983, and intermittently for several years prior to that. The survey was originally conducted with 32 standard gill nets, but additional nets were added in the late 1990s and early 2000s to mitigate sampling deficiencies, mainly in the offshore regions of the lake. Currently we sample the lake using 32 standard gill nets set in the near-shore areas, an additional 20 standard gill nets in the off-shore portions of the lake, 25 specialized forage gill nets randomly located throughout the lake, and 16 specialized Northern Pike gill nets located in shallow, weedy areas around the periphery of the lake. Periodically we also perform mark-recapture population estimates on the walleye population. Mark-recapture estimates are labor intensive and thus costly, so we have done seven of these estimates on about a five year rotation since 2002, with several estimates repeated in consecutive years to check repeatability of our results. We have found that the correlations between 14+ inch Walleye in the independent spring mark-recapture population estimates and the fall Walleye index are extremely strong; leading us to a conclusion that both methods of evaluating the adult Walleye population are showing the same trends. The latest spring mark-recapture population estimate occurred in 2018.
\n
\nWalleye catch per effort (CPE) has generally been increasing the last six years, since we experienced the lowest catches ever observed in 2012. The bulk of the Walleye catch continues to be driven by the extremely strong 2013 year class; however, we are now seeing improved age diversity with 2017, 2016, and 2014 year class Walleye also being sampled near or above median levels. 2014 year class fish were measured below average levels in our age 1 to age 3 year-class-strength index, but in 2018 they are now present at median levels, likely due to stringent harvest regulations that curtailed typical fishing mortality once they grew to sizes over 14 inches.
\n
\nThe CPE of Walleye longer than 20 inches is once again near median levels after being below median since around 2013. The increase of Walleye over 20 inches is being driven by the 2013 year class, where the faster growing females began to reach lengths in the 20+ inch size group during the 2018 growing season. While the percentage of Walleye in the 20+ inch size group is currently relatively normal, it will likely continue to increase as more of the 2013 year class is added to the current number of fish that have grown past this length.
\n
\nStill of major concern with the Mille Lacs Walleye population is the reduced average body condition (fatness), where we have been observing a general decline since around the late 1990s. Mille Lacs anglers have tended to realize excellent Walleye catch rates over the last couple of decades, particularly when body condition has been most reduced. Most strongly impacted have been the largest Walleye (> 20 inches), where regression analysis is showing an unusually strong relationship between angler catch rates and reduced robustness of catchable sized Walleye, suggesting that many of the large fish anglers have been observing in their recreational fishing is likely more a function of Walleye hunger, rather than Walleye numbers. Additional analysis bolsters the results observed in past diet studies; namely the importance of small Yellow perch in the diet of Walleye. In fact, the development of Walleye year classes to age 1 appears to be heavily reliant on strong numbers of small Yellow perch as well as the improved condition of their larger conspecifics; it's possible the two may be related.
\n
\nYellow perch remain near the lowest levels observed in Mille Lacs. Current metrics indicate that age 1 Yellow Perch is the only age class currently being observed above median levels. The 2017 year class of Walleye appears very strong, which is what we would typically expect with the amount of small Yellow perch forage that were available during their first year. More inexplicable is why the condition of large Walleye did not show improved body condition with the addition of the 2017 year class of Yellow perch. Some anecdotal reports suggested that 2017 Walleye condition did show improvement later in the fall after our September sampling. Whether the 2017 year class of Yellow perch can stay relatively intact to contribute meaningfully to the angler creel in a couple of years remains to be seen. Preliminary indications from the forage gill nets suggest little alternative forage from 2018 Yellow perch or age 0 Tullibee suggesting that the 2017 year class of Yellow perch is most likely destined to be consumed as forage by apex predators.
\n
\nWhile predation appears to ultimately decimate Yellow perch year classes at young ages, the main problem appears to be overall reduced productivity of the Mille Lacs ecosystem. Some stakeholders have postulated that too large of a population of large Walleye is responsible for excessive predation of forage fish, namely age 0 Yellow perch. If this type of top-down effect were actually occurring, we would predict that we should observe Walleye in excessive numbers, large declines in forage fish, large increases in zooplankton, and reduced algae. The reality is fall gill net sampling and spring mark-recapture population estimates both indicate a recovering Walleye population that is at moderate levels when compared to the last 35 years. Forage fish appear to have decreased dramatically; however, instead of observing the predicted increase in zooplankton that should have occurred with reduced prey fish we have observed a strong decline in zooplankton. Various indicators for algal levels suggest that primary production has decreased beginning around the mid-1990s and may still be declining. Two of the predictions for excessive numbers of Walleye creating top-down effects are exactly the opposite of what should occur.
\n
\nAn alternative explanation is we may be dealing with an ecosystem exhibiting bottom-up trophic effects. Predictions for changes that would occur across Mille Lacs' trophic levels should bottom-up impacts occur would be: algal production would decrease, zooplankton would then decrease, which in turn would decrease the amount of forage fish, which would then result in reduced numbers of apex predators. All current data agree with each of these predictions. Changes to the lowest trophic level began prior to the introduction of aquatic invasive species in Mille Lacs, but the addition of zebra mussels and spiny water flea have likely exacerbated some of the changes, particularly to the zooplankton community. Zooplankton numbers and biomass hit rock bottom from 2013 through 2016 and we are beginning to observe some modest increases the last couple years; however, small cladocerans, a major component of the zooplankton community and an important food resource for prey fish, remain severely depleted. It currently appears that the numbers and biomass of various species throughout all trophic levels are still adjusting to an overall amount of reduced productivity system wide, making it difficult to predict where we will ultimately \"stabilize\". What seems most likely at this point is that Mille Lacs will ultimately show less productivity in the amount of Walleye and Yellow perch that anglers had become accustomed to prior to the mid-1990s.
\n
\nThe changing conditions throughout Mille Lacs have likely made Mille Lacs more hospitable for Smallmouth bass. While we have observed decreasing Smallmouth bass numbers the last several years in our assessment gear, the population remains well above median levels. Our normal sampling gear is highly size selective towards Smallmouth bass under 16 inches and it becomes difficult to distinguish if changes in index numbers are a reflection of actual changes of abundance or if it's simply an indication of larger fish that are less susceptible to being caught. Creel results indicate that Smallmouth bass harvest is minimal, making fishing mortality an unlikely vector for reduced numbers. It's possible that Smallmouth numbers are simply adjusting to a more stable equilibrium with the rest of the fish community in Mille Lacs. In an attempt to discern if there are any changes to the size structure of the Smallmouth bass population that may be impacting the gill net index we will be looking at length frequency data from electrofished spawning adults in the spring of 2019 in order to determine if there is any discernable increase in the size of fish when compared to past years.
\n
The walleye population appeared quite healthy in 2004. The gill net catch rate was about average. Condition of the walleye was above average for medium and large fish, 12 year classes of females were represented in the spawning stock, and recruitment in recent years was certainly adequate. Weak 2000 and 2001 year-classes were the result of the nearly absent 2001 yellow perch year class. However, it is projected that strong 2002 and 2003 walleye year classes will be providing more than enough recruitment to compensate for the weaker year classes. Furthermore, it is likely that high forage abundance has reduced mortality through decreased angler success and possibly lower natural mortality. It is useful to compare the gill net catch in 2004 to the gill net catch in 1990, when the 1988 year class was age 2. The 1988 year class was the last exceptional year class prior to the 2002 year class. One of the most notable features of the 2004 length distribution from the gill nets was the relatively low numbers of walleye between 14 and 20 inches. There was a similar low abundance of medium-sized fish in 1990, although not as pronounced as in 2004. Another obvious similarity between the two years is the high abundance of age 2 walleye representing the 1988 and 2002 year classes. There were about the same number of age 2 fish in both years.There were also some noteworthy differences between the samples from these two years. First, the age 2 walleye were about 1 inch larger in 1990 than in 2004. Small fish grew slowly in 2004 because of a cold summer and low numbers of YOY yellow perch. Second, the 2003 year class of walleye appeared strong in 2004, while the age 1 walleye were below average abundance in 1990. Third, there were twice as many fish over 20 inches, and three times as many fish over 22 inches in 2004 than in 1990. In fact, the catch of fish over 20 inches in 2004 was 75% above the median, while the catch of large walleye in 1990 was 12% below the median. The build up of walleye over 20 inches in recent years was likely a result of regulations which usually included protected slots for walleye greater than 20 inches.The significance of these similarities and differences is important when considering how many walleye can be harvested over the next few years. It appears that the walleye population that is present in Mille Lacs today should be able to withstand most angling scenarios that can reasonably be expected over the next two or three years, as long as regulations continue to protect most of the fish over 20 inches, bag limits remain at 4 fish, and band fishing remains similar to recent years. Yellow perch numbers have increased as a new year class recruited to the gill nets. Poor recruitment since the 1996 year class culminated in almost no recruitment in 2001. However, the 2002 and 2003 year classes were strong. Although the 2002 year class initially grew quickly, growth rates were slow for younger perch in 2004. The consequences of the strong and weak perch year classes include well-conditioned medium and large walleye, but low-conditioned small walleye. This suggests that small walleye will be more susceptible to anglers during the winter fishery and the open-water fishery in 2005. Heavy predation may ultimately reduce the strength of the 2003 yellow perch year class. Tullibee gill net CPE increased dramatically in the offshore gill nets, but did not change in the inshore nets. Most of the increase was due to recruitment of age 1 tullibee. However, based on the 2003 survey, large numbers of age 2 tullibee were expected, but failed to show up in the inshore gill nets. Tullibee catches may be more subject to weather than most other species since they are more likely to suspend, and may move more between inshore and offshore habitats. More cool summers similar to 2004 will likely lead to improved abundance. Northern pike numbers have changed little in recent years. Anglers continue to report higher catches, however, likely as a result of the increase in release rate that has been observed since the protected slots were implemented in 1997. Anglers also reported some large muskellunge.
"},{"surveyType":"Targeted Survey","surveyID":"4501227140996000","headerInfo":{"wb_type":"Lake","wb_name":"Mille Lacs","id_date":"2012-05-15","wb_alt_name":"","wb_id":"48000200","survey_type":"Special Assessment","survey_id":"4501227140996000","county":"Mille Lacs"},"fishCatchSummaries":[{"quartileWeight":"N/A","averageWeight":"2.40","quartileCount":"N/A","totalWeight":628625,"gearCount":15.2333333333333,"CPUE":"37.88","totalCatch":577,"species":"SMB","gear":"Standard electrofishing"}],"lengths":{"SMB":{"maximum_length":21,"minimum_length":2,"fishCount":[[10,10],[11,8],[12,33],[13,46],[14,58],[15,84],[16,87],[17,63],[18,52],[19,54],[2,1],[20,35],[21,4],[4,1],[5,10],[6,12],[7,9],[8,6],[9,4]]}},"surveyDate":"2012-05-15","surveySubType":"Special Assessment","narrative":"Smallmouth Bass Electrofishing
\n
\nSpawning/staging smallmouth bass were sampled from 21 May, 2012 through 15 June 2012 via electrofishing. A total of 564 individual bass were caught and subsequently marked by removing the third dorsal spine in order to attempt a population estimate on recaptured fish the following spring (2013). Thirteen fish were recaptured during the initial marking phase, but a population estimate was not attempted as the marked fish had not had the opportunity to mix throughout the population after the initial mark was applied. Two hundred twenty-nine smallmouth bass were male, 224 were female, and 124 remained unidentified for sex. Fish lengths ranged from about three inches to 21.3 inches. The modal length for sampled fish was 16 inches, and over a third of the fish were greater than 17 inches.
\n
\nTable 31 and Figure 26 in the 2012 Mille Lacs Large Lake Report reference catch by station and the length frequency distribution of smallmouth bass, respectively, for this Special Assessment.
\n
The Mille Lacs Lake game fish community is primarily composed of walleye, yellow perch, northern pike, muskellunge, and smallmouth bass. Other game fish include largemouth bass, bluegill, pumpkinseed and black crappie. Common minnow species include spottail shiner and mimic shiner. Invasive animal species include common carp, zebra mussel, Chinese mystery-snail, banded mystery-snail, and spiny water flea. Curly-leaf pondweed and Eurasian watermilfoil are well established in the lake.
\n
\nCreel Survey
\n
\nFishing effort for the 2012-2013 winter season was 2.14 million angler-hours (ang-hrs), about 22% above average. Open water 2013 fishing effort was 863,000 ang-hrs, which is approximately 40% below average. A major impact to summer pressure in 2013 was the late ice-out in 2013, which occurred on 16 May, 5 days after opener. The change in regulations to a 2 fish limit and a harvest slot of 18-20 inches with only 1 allowed over 28 inches likely also affected total effort. Walleye harvest was relatively low at 74,650 lbs. Total kill was 141,500 lbs. Anglers released an additional 1,147,800 lb of walleye. Most of the harvested walleye were age 5 and age 6.
\n
\nAnglers harvested 6,850 lb of northern pike, and released 94,000 lb. Total kill for pike was 11,000 lb, similar to 2012. Regulations in 2013 had been liberalized to 33 to 40 inch protected slot, with 1 fish in a 3 fish bag allowed over 40 inches.
\nAnglers caught 73,200 smallmouth bass in 2013, which was the highest ever observed for Mille Lacs Lake. Approximately 1,630 smallmouth were harvested under the new liberalized 17 to 20 inch protected slot. Yellow perch harvest was 6,950 lb. Tullibee harvest was 2,380 lb.
\n
\nFall Assessment
\n
\nWalleye catch per effort (CPE) in the inshore gillnets was 8.7 fish/net and 11.3 lb/net. In offshore nets, walleye CPE was 19.2 fish/net and 27.5 lb/net. Catch per effort was almost two times as high as the previous year, but the increase was due to abundant and larger than normal age 0 walleye that were more susceptible to the smallest mesh of the gill nets. Age 1+ walleye catch was similar to the record lows that were observed in 2012. The CPE of walleye longer than 20 inches remained at moderate levels of around 2/net in the inshore nets and 4.5/net in the offshore nets. As observed in recent years, the 2000, 2001, 2004, 2009, 2010, and now the 2011 year classes are poorly represented in the gill nets, while 2005 through 2008 appear average. Early indications from electro-fishing suggest that the 2012 year class may be low and the 2013 year class has the potential to be above average. The proportion of mature walleyes that were male in inshore gill nets decreased to the lowest observed at 36%. The catch-per-effort of mature males in both the inshore and offshore nets decreased to the lowest level observed and the second lowest observed, respectively. The number of mature female walleye in the inshore nets remains similar to the last two years, and is near the lowest level observed since 1983. Mature females continue to be caught at a moderate level in the offshore nets, where CPE has remained relatively stable since these nets were first utilized in 1998. Walleye growth was around average for male and female walleye age 2-4 and below average for older males and females. Walleye condition was above average for walleye less than 14 inches and about average for walleye greater than 14 inches.
\n
\nNorthern pike increased in the inshore nets to a CPE of 2.8 fish/net, which is the highest observed since 1983. The increase was due mainly to high numbers of age 0 to age 2 fish, which caused the number of fish less than 28 inches to increase. However, fish greater than 28 inches remain at below average levels in the assessment nets. Similarly, the northern pike catch in the 16 specialized northern pike gill nets increased to a CPE of 8.1 fish/net, however, the magnitude of the increase was less than that observed in the inshore due to age 0 fish being too small to be effectively caught in the larger mesh sizes of the pike nets. Inshore nets sampled 9 year classes of northern pike, with age 0 and age 1 fish at the highest levels observed. Mark-recapture population estimates are planned for the spring of 2014, for both walleye and northern pike.
\n
\nYellow perch catch was similar to last year. CPE declined slightly in the inshore gillnets to the lowest observed since 1989 at 18.6 fish/net and 3.3 lb/net. Gill net CPE of perch larger than 9 in dropped for the second year in a row to 2.3 fish/net, a 66% decrease from the previous year. In the offshore nets, perch CPE increased from the previous year by about 35% to a CPE of 24.3 fish/net and 6.02 lb/net, but was still about half of the average catch.
\n
\nTullibee CPE increased from the lowest observed in 2012 to 0.8 fish/net and 0.6 lb/net in the inshore nets, which was still about 14 times below average. CPE decreased by 63% in the offshore nets to 7.7 fish/net and 10.1 lb/net. Seventy-eight percent of the tullibee caught in the gill nets were greater than three years old, with no strong year classes available to recruit into the spawning stock. Forage gill nets indicated relatively high levels of age 0 fish, although they appear to be small. The difference in magnitude between the inshore and offshore catches over the last several years may reflect a diminished population that is no longer over-flowing into the less desirable habitat of the near shore region, or it may represent a behavioral shift to offshore areas due to other environmental factors.
\n
\nOther species were also caught in standard gill nets, generally in low numbers. Smallmouth bass catch rate was the second highest observed in the inshore gill nets at 1.5 fish/net. Trends over the last decade show an increasing smallmouth bass population in the lake. Burbot continue to exhibit declining numbers, and are now only occasionally observed in the assessment nets. Rock bass increased for the third year in a row and remain at above average levels.
\n
\nIn addition to relatively strong numbers of age 0 tullibee in the forage gill nets, we also recorded the highest numbers of age 0 and age 1 yellow perch observed. Yellow perch and tullibee greater than age 1 were at low levels. Age 0 spottail shiners were at moderate levels, while age 1+ spottails were low. Bluntnose minnows were not observed at all in the forage nets. Age 0 walleye were observed at moderate to high levels, while no age 1+ walleye were recorded, which was the first time this has occurred in the forage nets.
\nThe CPE of YOY and age 1 yellow perch in the trawl were well below average; however, it appears that aquatic invasive species may be interfering with trawl catches, particularly in the Wealthwood area. The size of YOY perch caught in the trawl was slightly below average at 2.2 inches, which was similar to the average size of 2.4 inches that was observed in the electrofishing runs. Reduced angler catch rates for walleye beginning in July and the improved condition of predators caught in the fall sampling suggest that the higher forage levels observed in the forage gill nets are likely the better indicator of forage levels. If forage levels remain high into the open water season of 2014, anglers can expect a continuation of the reduced catch rates for walleye that were observed over winter.
\n
\nSpring Muskellunge Trap Netting
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\nSpring trap netting collected 122 muskellunge in 95 net sets for a total catch rate of 1.28 fish/net. No muskellunge were captured in the new net sets north of Hawksbill Point up towards Pine Island. The average length was 44.7 in, and 22 muskellunge (18%) were longer than 50 inches (Figure 1). The longest observed was 55.7 in. The muskellunge assessment will be repeated in 2014.
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\nInvasive Species
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\nZebra mussel density appears to have stabilized over the last three years, where it has averaged about 1100/ft2. Veliger (larval zebra mussels) densities continue to increase, with the 2013 mid-July samples showing the highest counts since sampling began in 2008.
\nSpiny water flea (Bythotrephes) was observed during each sampling period from May through September. Peak density occurred in September and was 11.9 Bythotrephes per sample, which was the highest observed since spiny water flea was first observed in the fall of 2009. Cursory spot checks of fish stomachs show that age 1+ tullibee and age 1+ yellow perch were consuming spiny water flea.
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\nIt appears that spiny water flea has taken a toll on zooplankton numbers and biomass. Native zooplankton are a vital dietary staple for many larval and juvenile fish in Mille Lacs. We have been observing severe declines in various species that belong to three broad functional groups. Currently, all three groups show some level of depletion, but small cladocerans show the greatest decrease, where in several months they are barely detectable in the samples. However, in 2013, the numbers of juvenile yellow perch and walleye both appeared to be high, suggesting either the low levels of small zooplankton are adequate at the appropriate time, or larval walleye and perch found alternative prey resources.
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\nMore detailed reports are available at http://www.dnr.state.mn.us/areas/fisheries/aitkin/index.html
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\tMille Lacs is a 128,251 acre lake that is relatively shallow with a maximum depth of 42 ft and an average depth of 28.5 ft. One of the lakes unique features is that about 70% of its shoreline is suitable Walleye spawning habitat. With its relatively close location to the Minneapolis/St. Paul metro area, Mille Lacs receives significantly more fishing pressure than several of the other large lakes in Minnesota. Despite the one Walleye limit, and catch and release seasons, angling pressure on the lake remains high with over 3,800,000 angling hours in the 2019-2020 fishing season. The high angling pressure can be attributed to strong Walleye and Smallmouth bass catch rates and the ability to land quality sized fish of several species throughout the lake. Winter months saw significantly higher fishing pressure than the open water season.
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\n Walleye is the primary targeted species by anglers on the lake. We have observed reasonably consistent natural reproduction over the last eight years with particularly strong year classes from 2013 and 2017. These two year classes make up a majority of what anglers currently catch on the lake. The large lake survey in 2020 found the most frequently sampled size of walleye in the lake was 17-21 inches, which are from the 2013 year class. Larger Walleye are present, but appear to be relatively weak, due in part to four consecutive failed year classes from 2009 - 2012. Walleye growth rates have slowed in Mille Lacs, likely due to reduced productivity in the system making it more difficult for the females of the strong 2013 year class to grow into the 24\"+ length classes.
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\nWalleye catch rates were highest in May and June, which is typical for Mille Lacs. Catch rates exceeded median levels throughout this time period; however, angling pressure was relatively low. Walleye catch rates slowed down in the latter portion of summer as a moderate Yellow perch year class became large enough for Walleye to prey upon as forage, making Walleye less prone to bite. In 2020, anglers harvested 66,750 lbs of Walleye, this also includes hooking mortality associated with released fish. 2021 regulations will allow anglers to harvest Walleye in the 21\" - 23\" inch size range during winter, May, and after mid-September. There is a planned Walleye closure in the first half of July to help reduce Walleye kill due to hooking mortality.
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\n\tThe Yellow Perch population in Mille Lacs has dramatically declined in the past decade but there are still jumbo sized Yellow Perch available in the lake. Yellow Perch in the 12-13 inch range were sampled in 2020, although they were observed at relatively low levels. Smaller Yellow Perch are an important forage species for most game fish in the lake and a moderate number of age 0 fish were sampled in the fall, mainly in the nearshore region of the lake.
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\n\tSmallmouth Bass are the second most targeted species in the lake with their popularity increasing on a national scale over the last several years, in part due to several highly visible national tournament held on Mille Lacs. Quality sized fish over 17\" and trophy sized fish over 20\" are readily available in rocky areas throughout the lake, where Smallies tend to feed on abundant crayfish, their most common prey. Regulations allow for the harvest of Smallmouth bass under 17\"; however, few anglers have opted to do so and exploitation rates remain low.
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\nThere is the opportunity to catch trophy sized Northern Pike and Muskellunge in Mille Lacs lake. Northern Pike over 42\" were sampled in the 2019 spring targeted survey. The 2020 spring survey was suspended due to COVID-19 related concerns; however, during the fall gill net sampling almost 30% of the Northern pike observed were over 30\" and 5% were over 40\". Mille Lacs maintain a low-density, high-quality Muskellunge population and anglers continue to report sighting and catching fish over 55 inches. Muskellunge regulations follow the normal statewide guidelines. In 2020 Mille Lacs received its biennial maintenance stocking of Muskellunge. Normally fingerlings are used when stocking; however, the 2020 stocking included a substantial number of \"holdover\" fish that are much larger and should show decreased predation by the lake's various piscivores.
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\nAnglers on Mille Lacs need to be aware of many special regulations as the regulations can be changed during the fishing season. Currently (starting in May 2021) all Burbot must be immediately released. Burbot are a cold-water species and Mille Lacs maintains very little cold-water habitat. Burbot are now sampled at trace levels in the lake and are likely being adversely impacted by longer summers and warmer water temperatures. The Smallmouth and Largemouth Bass limit is 3 combined daily and all fish greater than 17 inches must be immediately released. The limit of Tullibee or (Cisco) is 10 in possession. During the month of June all walleye must be immediately released and the targeting of Walleye is closed from July 1st - July 15th. This planned closure protects fish from hooking mortality and reduces the chance of an unplanned closure later in the year. Starting July 16th Walleye may again be targeted but must be immediately released through September 15th. From September 16th - November 30th, one walleye between 21\"-23\" may be harvested or one over 28 inches. All Northern Pike greater than 30\" must be immediately released, with a possession limit of 3. The Northern Pike season is extended through March 31st 2022. These regulations apply to all tributaries of the lake to the posted boundary.
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\nStarting July 1st anglers targeting Northern Pike and Muskellunge may use live bait that is greater than 8 inches, all other anglers must use artificial baits. A night closure is in place from 10pm - 6am until September 15th. This night closure does not apply to anglers targeting northern Pike or Muskellunge with baits greater 8 inches. Bow fishing is also exempt from the night closure, but angling equipment cannot be possessed while bow fishing.
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\nLastly, Mille Lacs has been designated as an infested water for a number of invasive species. Make sure you drain, clean and dry your boat when you leave any water body to prevent the spread of aquatic invasive species. To help maintain Mille Lacs lakes trophy fish populations, catch and release fishing will help to sustain these populations.
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AT PRESENT THE LAKES WALLEYE POPULATION IS DOMINA- TED BY THE 1979 AND 1984 CLASS WALLEYE. THE 1984 YEAR CLASS WALLEYE WILL BE NEARING EXCEPTIBLE SIZE TO THE ANGLER THIS YEAR AND SHOULD DOMINATE THE 1987 ANGLER CATCH. THE 1979 YEAR CLASS IS STILL ABUNDANT AND SHOULD PROVIDE HIGH QUALITY FISH TO KNOWLEDGEABLE ANGLERS. THE NOP POP. APPEARS TO BE STABLE WITH LITTLE VARIATION IN ABUNDANCE AND SIZE IN RECENT YEARS. ADULT PERCH ABUNDANCE IS NEAR MEAN CATCHES OBSERVED SINCE 1972. TULLIBEE CATCH WAS HIGH, AND NEAR NORMAL HIGHS OBSERVED SINCE 1972.
","surveySubType":"Population Assessment"},{"headerInfo":{"id_date":"1997-09-30","wb_alt_name":"","wb_name":"Mille Lacs","wb_type":"Lake","survey_id":"113586","county":"Mille Lacs","survey_type":"Population Assessment","wb_id":"48000200"},"surveyType":"Standard Survey","surveyID":"113586","surveyDate":"1997-09-30","fishCatchSummaries":[{"species":"TLC","totalCatch":214,"gear":"Standard gill nets","averageWeight":"0.38","quartileCount":"4.9-17.6","quartileWeight":"0.4-0.5","CPUE":"6.69","totalWeight":81.53,"gearCount":32},{"gear":"Standard gill nets","totalCatch":12,"species":"BUB","gearCount":32,"totalWeight":15.99,"CPUE":"0.38","quartileWeight":"1.1-2.1","averageWeight":"1.33","quartileCount":"0.0-0.2"},{"species":"NOP","totalCatch":45,"gear":"Standard gill nets","quartileCount":"0.9-4.3","averageWeight":"5.15","quartileWeight":"2.4-4.3","CPUE":"1.41","totalWeight":231.94,"gearCount":32},{"species":"BLB","totalCatch":14,"gear":"Standard gill nets","averageWeight":"0.28","quartileCount":"0.0-4.7","quartileWeight":"0.4-1.0","CPUE":"0.44","totalWeight":3.87,"gearCount":32},{"CPUE":"0.41","totalWeight":22.89,"gearCount":32,"averageWeight":"1.76","quartileCount":"0.8-2.4","quartileWeight":"1.6-2.1","gear":"Standard gill nets","species":"WTS","totalCatch":13},{"averageWeight":"1.65","quartileCount":"3.3-14.8","quartileWeight":"0.9-1.5","CPUE":"12.31","totalWeight":650.29,"gearCount":32,"species":"WAE","totalCatch":394,"gear":"Standard gill nets"},{"quartileWeight":"0.8-1.5","averageWeight":"0.92","quartileCount":"0.0-0.2","gearCount":32,"totalWeight":0.92,"CPUE":"0.03","totalCatch":1,"species":"SMB","gear":"Standard gill nets"},{"averageWeight":"0.59","quartileCount":"0.1-1.1","quartileWeight":"0.6-1.1","CPUE":"0.03","gearCount":32,"totalWeight":0.59,"species":"YEB","totalCatch":1,"gear":"Standard gill nets"},{"quartileWeight":"0.2-0.3","averageWeight":"0.22","quartileCount":"9.9-57.1","totalWeight":825.74,"gearCount":32,"CPUE":"116.91","totalCatch":3741,"species":"YEP","gear":"Standard gill nets"}],"lengths":{},"narrative":"PRESENT FISH POPULATION STATUS: Walleye abundance (numbers and biomass) as indicated by assessment gill netting was below average. The 1996 year class accounted for 27% of the catch in the gill net sample (102 fish). If this is representative of the population, the 1996 year class is the strongest that has been observed since the 1988 year class. However, the variability in the gill net catch was high, so the uncertainty is also high. The 1995, 1994, 1993, 1992, 1991, and 1988 year classes contributed between 10 and 20%. The index of year class strength indicates near average recruitment for 1991 through 1994. SUMMARY BY SAMPLING METHOD:Spring trap netting: Between April 15 and May 8, 1997 we captured 2,165 northern pike of which we tagged 1,609 (including 347 that were double tagged to estimate tag loss). There were 197 recaptures from the 1994, 1995 and 1996 tagging periods. Pike appeared to be of similar abundance to the previous year. The sum of the population estimates for each individual tagging zone was 32,065 (14,493-49,637), compared with 30,896 (14,127- 47,665)in 1996. Lakewide estimates (dervived from recaptures from throughout the summer)was lower [24,708(18,510-32,922)], although the confidence intervals overlapped with the spring estimate. We also caught 337 muskellunge of which 264 were tagged, and 66 were recaptures from 1996. Homing was not as evident in muskellunge as it has been in northern pike, yet, of the recaptures 69-81% had been tagged in the same or adjacent areas in 1996. To date we have received information from anglers who caught over 626 tagged northern pike and 14 tagged muskellunge.The catch rate during the 1997 musky assessment was about 1.8/net, which was similar to what was observed in 1994 (2/net), 1995 (1.7/net), and 1996 (1.8/net). The number of large individuals continued to increase. One of 250 in 1992 was over 45\", six of 163 in 1993, 17 of 256 in 1994, 25 of 205 in 1995, 55 of 305 in 1996, and 65 of 337 in 1997. Two fish were sampled that were over 50\". The longest was 50.3\" and weighed 36.3 pounds. We also captured 1 yearling muskellunge, which was naturally reproduced (no fish were stocked in 1996). Evidence of natural reproduction of muskellunge in Mille Lacs has been documented each year since 1991.Spring trawling: Trawling for yearling walleye and yellow perch has been conducted in spring since 1992. The objective was to evaluate size distributions and abundance after winter mortality had occured. In the spring of 1997, the abundance of 1996 year class walleye actually increased in the trawl catches suggesting that either the low numbers observed in the previous fall were not representative of the population, or sampling was inadequate. Considering that all other year classes either decreased or remained the same over winter (with an average of 47% overwinter survival), I believe that the fall of 1996 trawl sample underestimated abundance. This supports the hypothesis that the clear water decreases the trawl catchability.Summer seining: No walleye were sampled in the seine. Size of YOY yellow perch appeared above average, and there abundance did not seem to be below average. August night electrofishing and Fall trawling: The total walleye trawl CPUE continued to decline. The catch of all ages of walleye was the lowest ever observed (46). Young of year walleye (29) were caught at the third lowest rate that has been observed since the trawl assessment began in 1972. The extremely clear water (10-12ft secchi) likely impacted the efficiency of the trawl. Average length of YOY walleye was similar to the last several years (5.5\"). Electrofishing results suggest that the 1997 year class is similar in abundance to 1996. Although the 1996 year class was suspect of being below average in 1996, information from other sources in 1997 suggest that it may be near or above average in strength. The trawl CPUE of YOY yellow perch was near average, and there have been no measurable relations between clarity and YOY perch catch rates. Fall gill netting: Walleye CPUE (12.3/net) did not change much from last year (13.1/net). A very high catch of yearling walleye (1996 year class) accounted for over 25% of the total sample. This high catch of 1996 year class fish suggests that the trawl sample of 1996 was not representative of the population, or sampling was inadeqaute, or a combination of both. The variability between nets was higher than normal; therfore, the uncertainty regarding this index is also higher than in past years. Yellow perch CPUE (116.9/net, 25.8 pounds/net) was the highest ever recorded. The 1993 and 1994 year classes accounted for the majority of the catch. The catch of perch over 8\" and over 10\" were the highest that we have observed, and were due to the abundant 1993 and 1992 year classes. Northern pike CPUE (1.4/net) was up from previous years. The apparent increase in pike abundance is likely due to the abundant 1993 year class, which accounted for 36% of the sample. Creel survey: The 1997 open water angling effort (1,337,429 angler hours), walleye harvest (236,050 lbs), and catch rates (0.08/hour, 0.18 lbs/hour) were substantially lower than in 1996. This was due to the reduced abundance of walleye and to the new 15\" minimum size regulation that was implemented to ensure harvest did not exceed 280,000 pounds for the year. Cold weather in May, which reduced catch rates, also affected effort. Total annual harvest was reduced to 266,102 pounds. Total reduction due directly to the regulation was 62,000 pounds. It is unknown to what extent the new regulation affected effort because of the abnormally cold May; this confounded the analysis. However, it is likely that effort was affected by the regulation to some degree in two ways. 1) Anglers may not have fished Mille Lacs because of the regulation, and 2) the regulation reduced harvest rate, which in turn reduced effort (harvest rate is strongly correlated to fishing effort). An evaluation of the catch rates suggest that the affect of the regulation on effort was a reduction by less than 200,000 hours. Had there been no new regulation, the harvest rate would have been 0.22 pounds /hour instead of 0.18 pounds/hour. At a harvest rate of 0.22 pounds/hour the expected effort would have been about 190,000 hours higher than we observed. This suggests that the new regulation reduced effort by about 190,000 hours (due to a reduction in harvest rate -#2 above). May effort was about 175,000 hours below average, due to poor catch rates and cold weather. An addition of 365,000 hours of effort would have increased total harvest to 409,000 lbs. for the year, with no new regulation. This is the same value that was predicted by the catchable population prediction model. This also suggests that effort was not decreased significantly just from the presence or the regulation (#1 above). Had effort been decreased as described above, there should have been a greater difference between the new expected harvest and the predicted harvest. Although total harvest of walleye was below average, the open water catch and harvest of walleye over 20 inches was not. Catch rates for large walleye were actually above average, the third highest that we have observed since 1985. As in 1996, the \"one over 20 inches\" size regulation had a greater impact than in the first eleven years that the regulation has been in place. About 27% of these large walleye were released (15% voluntary, 12% due to regulation). From 1985 to 1995 the percent of releases due to the regulation averaged 2.4% (0-5.6%), compared with 14.5% in 1996 and 12% in 1997. Open water yellow perch harvest remained about the same as the last several years (34,036 lbs), as did the number of perch released (212,269 fish). Most of the perch harvest occurs in winter and early spring (177,774 lbs.). Pen water catch of northern pike (7,784) and harvest (2,736 fish, 14,398 lbs) were also near average. Muskellunge anglers again experienced excellent angling. The total catch of muskellunge was 1,029 fish, similar to last years 1,059 fish. No harvested muskellunge were observed in the creel survey, however, 1 out of the 8 tag returns from anglers was from a harvested musky. Since reporting rates are higher for harvested musky, the maximum number of fish harvested would be 128 fish. If reporting rates of released fish were similar for northern pike and musky, then the number of musky harvested in 1997 was 45 fish. This is similar to past estimates from the creel survey when harvested fish were observed. The mean size caught by anglers that were interviewed in the creel survey was 37.8\", and 48% were over 40\". The largest fish reported released by an angler in the creel was 44\"; although, a 47\" tagged fish was reported to us, and fish as large as 51\" have been reported in newspapers and periodicals. Pressure directed at muskellunge or muskellunge in combination with other species appeared to level off. In 1997, creel clerks sampled 1,149 hours of effort compared with 1,314 hours in 1996, 654 hours in 1995, 536 hours in 1994, 358 hours in 1993 and 202 hours in 1992.
","surveySubType":"Population Assessment"},{"surveySubType":"Large Lake Survey","narrative":"The Mille Lacs Lake game fish community is primarily composed of Walleye, Yellow Perch, Northern Pike, Muskellunge, Tullibee, and Smallmouth Bass. Other game fish include Largemouth Bass, Bluegill, Pumpkinseed and Black Crappie. Common minnow species include Spottail Shiner and Mimic Shiner. Invasive animal species include Common Carp, Zebra Mussel, Chinese Mystery-snail, Banded Mystery-snail, and Spiny Water Flea. Curlyleaf Pondweed and Eurasian Watermilfoil are well established in the lake.
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\nCreel Survey
\nFishing effort for the 2014-2015 winter season was 1,486,500 angler-hours (ang-hrs), about 13% below average. An additional 42,00 angler-hours were observed once Walleye season closed in late February. Ice fishing pressure improved from the previous year due to ice conditions that allowed anglers to begin accessing the lake in late November, a relatively strong Walleye bite, and new regulations that liberalized Northern Pike bag limits and allowed spearers to legally pursue their sport for the first time since 1983.
\nOpen water 2015 fishing effort was 464,000 ang-hrs, which was approximately 66% below average and the lowest observed. Open water night effort was the lowest observed, mainly due to an extended night closure that was in place through the open water season. Open water day pressure was low throughout all periods of the summer; most likely due to restrictive walleye regulations and an early August Walleye closure due to exceeding the 2015 allocation of 26,800 pounds.
\nWalleye harvest, for the entire season, was the second lowest observed at around 12,000 lbs. Total kill, which includes hooking mortality, was 32,500 lbs. Anglers released an additional 218,350 lb of Walleye.
\nAnglers harvested 38,000 lb of Northern Pike, the highest observed since 1990. The increase in Northern Pike harvest was mainly due to liberalized regulations that allowed for winter spearing. An additional 46,000 lb of Northern Pike were released. Total kill for Pike was 39,950 lbs.
\nYellow Perch harvest was extremely low at 9,200 lb, and Tullibee harvest was similarly low at 10,550 lb. Anglers caught 87,400 Smallmouth Bass in 2015, which was the highest ever observed for Mille Lacs Lake. Approximately 5,175 Smallmouth were harvested.
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\nFall Assessment
\nWalleye catch per effort (CPE) in the inshore gillnets was 8.7 fish/net and 15.6 lb/net. In offshore nets, Walleye CPE was 10.1 fish/net and 19.9 lb/net. Catch per effort in the inshore nets remained low and was similar to the previous year. Numbers and biomass in the offshore nets decreased to the second lowest observed. The bulk of the Walleye catch came from the 2013 year class with only age 2 Walleye being observed at above median levels in the gill nets. The CPE of Walleye longer than 20 inches increased to 2.0/net in the inshore nets but were still below median levels, while the catch rate in the offshore nets, which have a much shorter history, remained near the lowest observed at 2.8/net. The CPE of mature males remains near the lowest observed in both the inshore and offshore nets and current numbers are a continuation of a decreasing trend that appears to have begun in the early to mid-1990s. Likewise, mature female CPE was the third lowest observed in the inshore and the lowest observed in the offshore nets and continues to exhibit a decreasing trend that began sometime after 2007. Walleye condition was the lowest observed for fish less than 20 inches but was the second highest observed for Walleye greater than 20 inches, suggesting that forage for small fish may be in low abundance.
\nNorthern Pike CPE in the inshore nets at 1.6 fish/net remained above the median despite a 40% decrease from the historical high of 2.75 fish/net observed the previous two years. Over 60% of the fish were from the 2012 and 2013 year classes, which made up the majority of fish less than 28 inches. Fish greater than 28 inches have remained relatively consistent the last three years at near average levels. The Northern Pike catch in the 16 specialized Northern Pike gill nets decreased by 8% to a CPE of 8.3 fish/net and 37.3 lb/net, which are both just below median.
\nYellow Perch CPE increased to median levels in the inshore nets to 43.9/net and 8.4 lb/net. Gill net CPE of Perch larger than 9 inches increased to 3.5 fish/net, but is still well below the median of 11.5 fish/net. Yellow Perch CPE in the offshore nets increased to near median levels at 35.3/net and 9.5 lb/net. The majority of Yellow Perch observed in both the inshore and offshore nets were from the 2013 year class.
\nTullibee CPE increased to 10.9 fish/net and 3.5 lb/net in the inshore nets, both over the 75% quartile for Mille Lacs Lake. CPE also increased in the offshore nets to 83.8 fish/net and 38.2 lb/net, which was the highest observed. Tullibee catch tended toward younger fish with over 75% of the fish observed in the inshore nets coming from the 2014 year class and 20% from the 2013 year class. The offshore nets were slightly more age-diverse with 58% of the Tullibee coming from the 2014 year class and 30% from the 2013 year class. The difference in magnitude between the inshore and offshore catches over the last several years may reflect a diminished lake-wide population that is no longer over-flowing into the less desirable habitat of the near shore region, or it may represent a behavioral shift into offshore regions due to other environmental factors.
\nBurbot continued to exhibit a declining trend in number, and are now only occasionally observed in the assessment nets. Rock Bass increased to 1.4/net, which is over twice the median level. Smallmouth Bass increased to the highest observed at 2.3/net in the inshore nets. Similarly, Smallmouth Bass continued to incrementally increase in the offshore nets and are also at the highest observed at 0.45/net. Trends over the last decade continue to suggest an increasing Smallmouth Bass population in the lake.
\nThe major prey species of piscivorous predators in Mille Lacs is generally small Yellow Perch. Annual fall sampling using small-mesh forage gill nets indicated that moderate numbers and biomass of young-of-the-year (YOY) Yellow Perch were available in 2015 when compared to the nine year history of this sampling gear. Age 1 Yellow Perch were at the lowest level observed, which remained consistent for this year class as they were also observed at the lowest level the previous year as age 0 fish. Conversely, age 2 Yellow Perch remained strong in both numbers and biomass at the highest observed over the relatively short history of the forage net sampling. Age 0 Tullibee were observed at moderate numbers and biomass, while age 1 Tullibee were at the highest observed. Moderate numbers of Spottail Shiners were also observed.
\nAge 0 and age 1 Walleye were observed at relatively low numbers and biomass, while 2013 Walleye continue to be caught at the highest observed. Overall, the forage nets would suggest reasonable forage availability for all sizes of Walleye. However, the low condition observed in Walleye less than 20 inches that were captured in the fall gill nets suggests that smaller and mid-size Walleye are not readily utilizing the available small forage. Larger Walleye, on the other hand, appear to be taking full advantage of the larger prey items available to them as suggested by the high condition factor (plumpness) that was observed in the fall sampling.
\nAge 0 Walleye CPE in the six electrofishing transects was below median levels for the second consecutive year at 96.0/hr and 56.4/mile. However, this level of abundance has previously been sufficient to produce a decent year class, as long as survival is above average. Average length for age 0 Walleye was about a half inch below average at 5.04 inches. Age 1 Walleye CPE was slightly below the median at 11.7/hr and 8.4/mile. The average length of age 1 Walleye was also about a half inch below average at 8.6 inches. Forage electrofishing runs of two minutes duration showed low to moderate numbers of age 0 Yellow Perch and moderate to high numbers of age 1 Yellow Perch. Catches of other species were relatively unremarkable in the five year history of forage sampling, although we did observe the highest catch of age 0 Black Crappie and Mottled Sculpin.
\nTrawling was expanded in 2014 to cover more areas throughout the lake and to sample additional habitat types. Of the twenty-three locations sampled, age 0 Yellow Perch were the most plentiful species observed at 414.9 fish/hr, however, 85% were captured at a single site and were observed along only four separate trawl transects. Average length of the YOY Yellow Perch was 2.57 inches. The second most observed fish was Spottail Shiner with a CPE of 6.9 fish/hr. Spottails also were collected at only four different trawl sites. Two YOY Walleye were caught while trawling and their average length was 4.02 inches. One 2013 year class Walleye was observed and its length was 12.2 inches.
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\nInvasive Species
\nZebra Mussel density peaked in 2012 at 1,270/ft2 and has been decreasing the last three years to a density of about 790/ft2 in 2015. These types of oscillations are not uncommon with recently colonized invasive species as they tend to overshoot carrying capacity before settling in to a more stable population density. Veliger (larval Zebra Mussels) densities were relatively low to moderate through much of the open water season, but the highest veliger counts observed since Zebra Mussels were first discovered in Mille Lacs, occurred in early July of 2015.
\nSpiny Water Flea (Bythotrephes) was observed during each sampling period from May through September. Peak density occurred in mid-June at 15.1 Bythotrephes per sample, which was the highest observed since Spiny Water Flea was first observed in the fall of 2009. Cursory spot checks of fish stomachs show that age 1+ Tullibee and age 1+ Yellow perch are consuming Spiny Water Flea.
\nIt appears that Spiny Water Flea have taken a toll on zooplankton numbers and biomass. Native zooplankton are a vital dietary staple for many larval and juvenile fish in Mille Lacs. We have been observing severe declines in various species that belong to three broad functional groups. Currently, all three groups show a severe level of depletion, but small cladocerans and large cladocerans show the greatest decrease, where throughout the summer they are now often barely detectable in the samples.
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The Mille Lacs Lake game fish community is primarily composed of Walleye, Yellow Perch, Northern Pike, Muskellunge, Tullibee, and Smallmouth Bass. Other game fish include Largemouth Bass, Bluegill, Pumpkinseed and Black Crappie. Common minnow species include Spottail Shiner and Mimic Shiner. Invasive animal species include Common Carp, Zebra Mussel, Chinese Mystery-snail, Banded Mystery-snail, and Spiny Water Flea. Curlyleaf Pondweed and Eurasian Watermilfoil are well established in the lake.
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\nCreel Survey
\nFishing effort for the 2015-2016 winter season was 1,167,500 angler-hours (ang-hrs), about 33% below average. An additional 9,250 angler-hours were observed once Walleye season closed in late February. Ice fishing pressure decreased from the previous year due to late ice-up, which occurred in late December, and poor travel conditions which restricted travel on the lake.
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\nOpen water 2016 fishing effort was approximately 520,000 ang-hrs, which was approximately 62% below average and the second lowest observed. Open water night effort was the lowest observed, mainly due to an extended night closure that was in place through the open water season. Open water day pressure was below median level throughout all periods of the summer, with the exception of October; most likely due to restrictive Walleye regulations and an early September Walleye closure due to exceeding the 2016 allocation of 28,600 pounds. October pressure increased, in part, due to a highly successful nationally televised BASS tournament in late September that attracted the attention of additional bass anglers.
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\nWalleye harvest, for the entire season, was the lowest observed at around 1,600 lbs with harvest only allowed during winter under an 18\"-20\" harvest slot. Total kill, which includes hooking mortality, was 36,350 lbs. Anglers realized an exceptional Walleye catch rate and released an additional 513,250 lb of Walleye.
\nAnglers harvested 18,950 lb of Northern Pike, which was half that observed the previous year. The decrease in pike kill occurred in the winter fishery and was likely influenced by ice conditions and a change in regulations that made it more difficult to harvest larger fish. An additional 59,500 lb of Northern Pike were released, which created a hooking mortality estimate of about 3,000 lb and a total kill of 22,000 lbs.
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\nYellow Perch harvest was extremely low at 5,100 lb, and Tullibee harvest was similarly low at under 2,000 lb. Anglers caught 128,250 Smallmouth Bass in 2016, which was the highest ever observed for Mille Lacs Lake and an increase of almost 50% over the previous high catch in 2015. Approximately 2,300 Smallmouth were harvested.
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\nFall Assessment
\nWalleye catch per effort (CPE) in the inshore gillnets was 9.8 fish/net and 14.3 lb/net. In offshore nets, Walleye CPE was 11.6 fish/net and 21.9 lb/net. The bulk of the Walleye catch came from the 2013 year class with only age 3 Walleye being observed at above median levels in the gill nets. The relatively small increase in the number of Walleye caught in the fall of 2016 when compared to last year's sampling event, likely represents an increase of selectivity of the fishing gear as the individual fish of the 2013 year class continue to grow larger and become more vulnerable to the gill nets. The CPE of Walleye longer than 20 inches decreased by 26% in the inshore nets, but increased by 20% in the offshore nets. The CPE of mature males increased in 2016 due to the maturation of most of the males of the strong 2013 year class; however, mature male CPE remains at a relatively low level. Mature female CPE has shown little change over the last three years and remains at the lowest observed. The biomass of mature females declined in both the nearshore and offshore nets, which is likely is a strong indication of the poor condition (fatness) of Walleye in the fall of 2016. Walleye condition on fish greater than 20 inches went from one of the best observed in 2015 to the second lowest observed in 2016. This prominent change in the robustness of larger Walleye was likely due to a strong decline in eatable size age 1 Tullibee, which grew larger than the gape limitation of the larger Walleye through 2016 and were not replaced with an appreciable contemporary year class of available forage. Surprisingly, the smallest size class of Walleye (<14 inches) showed an increase in condition, but they too remain below average condition. Medium sized Walleye (14-20 inches) showed little change in condition and remain near the lowest condition observed for this size class of fish. Low condition for all size classes of Walleye are a strong indicator of reduced forage availability in Mille Lacs and will likely result in continued high angler catch rates until forage levels become replenished.
\n
\nNorthern Pike CPE in the inshore nets at 1.6 fish/net remained unchanged from last year and is above the median. Almost 60% of the fish were from the 2012 and 2013 year classes, which made up the majority of fish less than 28 inches. Fish greater than 28 inches showed a strong increase in 2016, which appears to be due to the larger females of the 2012 and 2013 year classes growing into this quality size range. Five age 0 Northern Pike were caught in the inshore nets, which may be a harbinger of another above-average year class. The Northern Pike catch in the 16 specialized Northern Pike gill nets decreased for the second year in a row to a CPE of 7.7 fish/net and 38.9 lb/net, which are both just below median.
\n
\nYellow Perch CPE decreased by about half and are now below median levels in the inshore nets at 20.4/net and 4.8 lb/net. Gill net CPE of perch larger than 9 inches increased for the second consecutive year to 3.5 fish/net, but is still well below the median of 11.3 fish/net. Yellow Perch CPE in the offshore nets also decreased by about half to 18.6/net and 6.4 lb/net, which are both below median. Most of the Yellow Perch observed in both the inshore and offshore nets were from the 2013 year class, however a fairly large percentage of the fish observed in the nearshore nets were from the 2015 year class.
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\nTullibee CPE changed little for numbers of fish in the inshore nets at 9.6 fish/net; however biomass increased 2.5 times to 8.7 lb/net in the inshore nets, both metrics are over the 75% quartile for Mille Lacs Lake. CPE decreased by almost 55% in the offshore nets to 38.9 fish/net while biomass remained about the same at 38.4 lb/net, which is the highest observed. Tullibee catch tended toward younger fish in 2015 but was mostly 2+ aged fish in 2016. The majority of Tullibee were from the 2014 year class with fish ranging from 10.5 inches to 13 inches, making them less vulnerable to all but the larger piscine predators (Northern Pike and Muskellunge). The difference in magnitude between the inshore and offshore catches over the last several years may reflect a diminished lake-wide population that is no longer over-flowing into the less desirable habitat of the near shore region, or it may represent a behavioral shift into offshore regions due to other environmental factors.
\n
\nBurbot continued to exhibit a declining trend in number, and are now only occasionally observed in the assessment nets. Rock Bass showed little change at 1.3/net, which is at the 75% quartile for this species. Smallmouth Bass decreased from the highest observed at 2.3/net in 2015 to 1.4/net in the inshore nets in 2016, which is still above the 75% quartile. Smallmouth Bass continued to incrementally increase in the offshore nets and are at the highest observed at 0.70/net. Trends over the last decade continue to suggest an increasing Smallmouth Bass population in the lake.
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\nThe major prey species of piscivorous predators in Mille Lacs is generally small Yellow Perch. Annual fall sampling using small-mesh forage gill nets indicated that moderate numbers and biomass of young-of-the-year (YOY) Yellow Perch were available in 2016 when compared across the seven year history of this sampling gear. Age 1 and age 2 Yellow Perch were below median level. Age 0 Tullibee were observed at moderate numbers and biomass, while age 1 Tullibee went from the highest observed to near the lowest observed. Spottail Shiners were above median level and have generally been increasing over the last three years.
\n
\nAge 0 and age 1 Walleye were observed at moderate numbers and biomass. Overall, the forage nets would suggest reduced forage availability for all sizes of Walleye. However, the increased condition observed in Walleye less than 20 inches that were captured in the fall gill nets suggests that smaller and mid-size Walleye are utilizing the available small forage, but are still not finding adequate amounts of food. Larger Walleye appear to be having an even more difficult time finding adequate food resources.
\n
\nAge 0 Walleye CPE in the six electrofishing transects was highly variable in 2016, with the lowest catch rate and highest catch rate coming from the same location over two separate weeks. Overall CPE for YOY Walleye was 208.5/hour, which is close to twice the median and suggests that spring reproduction and survival were adequate up through fall. Catch rates for age 1 Walleye was less than half the median at 5.0 Walleye/hr, which suggests a relatively weak 2015 year class. Average length for age 0 Walleye was 5.2 inches, which spanned an extremely wide range of 3.2 inches to 8 inches. The average length of age 1 Walleye was relatively high at 9.7 inches. Forage electrofishing runs of two minutes duration showed comparatively high numbers of age 0 Yellow Perch and low numbers of age 1 Yellow Perch. Catches of other species were relatively unremarkable in the six year history of forage sampling, although we did observe above median catches of Spottail Shiners and Bluntnose Minnows.
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\nWalleye Fry Stocking
\nWalleye fry stocking was initiated in the spring of 2016. Relatively small numbers of Walleye fingerlings had been stocked previously in Mille Lacs from the years of 1945 through 1973. The current fry stocking is being done to ensure that we have adequate techniques in place to rear appropriate numbers of fry from Mille Lacs' unique genetic strain of fish in case an actual need for augmentation arises in the future. Further, we are marking stocked fry with an oxytetracycline (OTC) chemical signature that is absorbed into the bony structures, which allows us to later identify stocked fry in order to calculate a simple Peterson mark-recapture estimate of the number of natural fry that are currently being produced in the lake.
\n
\nCollection of adult brood stock occurred over a five day period, in mid-April, in the southeast quadrant of Mille Lacs from lake spawning fish. Approximately 244 quarts of fertilized eggs were collected and incubated in the St. Paul hatchery under a temperature regime that mimicked water temperatures in Mille Lacs. This would allow natural fry and stocked fry to hatch out at the same time, which would leave both groups of fish susceptible to similar environmental conditions once the marked fry were stocked back into the lake.
\n
\nHatchery fry began to hatch after about three weeks and ten million fry were subsequently immersed in an OTC bath and stocked into Mille Lacs in various locations in early to mid-May. An additional 250,000 marked fry were stocked in efficacy ponds so that we could evaluate the quality of the OTC marks.
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\nThroughout the month of September 1,207 YOY Walleye were collected from Mille Lacs and 115 age 0 Walleye were collected from the efficacy ponds. All useable otoliths from the efficacy ponds showed a bright clear OTC mark, indicating that the marking procedure was successful and that the marks were highly recognizable. Useable otoliths were retrieved from 1,165 of the sampled age 0 Walleye from Mille Lacs and we were able to discern OTC marks on 47 of the fish, indicating a marked fraction of 4% in the lake. The simple Peterson estimator would suggest that 233,000,000 natural fry were produced in 2016. This would equate to over 7,000 natural fry per littoral acre, which is relatively high when compared to other Walleye lakes. Further, this amount of fry production and survival resulted in fall electrofishing catch rates that were relatively high, which would indicate that with the first year of data there is no current evidence to suggest Mille Lacs Walleye are reproduction limited. Fry stocking is slated to continue for several more years, which will provide additional data on the variability of natural fry production.
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\nInvasive Species
\nZebra Mussels were not sampled in 2016. Zebra Mussels appear to have peaked in 2012, so we are now switching to a biennial sampling cycle. We do still collect Zebra Mussel veliger counts in our normal zooplankton tows and peak veliger densities in 2016 occurred in early July, when we observed the third highest count since sampling began in 2008.
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\nSpiny Water Flea (Bythotrephes) was observed during each sampling period from May through September. Peak density occurred in mid-June at 9.8 Bythotrephes per sample, which is the fourth highest observed since Spiny Water Flea was first observed in the fall of 2009. Cursory spot checks of fish stomachs show that age 1+ Tullibee and age 1+ Yellow Perch are consuming Spiny Water Flea.
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\nIt appears that Spiny Water Flea have taken a toll on zooplankton numbers and biomass. Native zooplankton are a vital dietary staple for many larval and juvenile fish in Mille Lacs. We have been observing severe declines in various species that belong to three broad functional groups. Currently, all three groups show a severe level of depletion, but small cladocerans and large cladocerans show the greatest decrease over time, where throughout the summer they are now often barely detectable in the samples. An unusual observation for 2016 was that the large cladoceran, Daphnia galeata mendotae, actually showed up in June at the highest density observed since June of 2013, before depleting again to barely detectable levels in the latter part of summer.
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\nOverview
\nWhen all available data are considered together, it appears that aquatic organisms in Mille Lacs are being impacted due to changing abiotic conditions and a bottom-up trophic cascade. The evidence of increasing annual water temperature is suggested in the opposing trends exhibited by Burbot and Smallmouth Bass. Burbot, an obligate cold-water species, have been declining since the mid 1980's, whereas Smallmouth Bass, which tend to find warmer water to be more suitable, have been increasing since the late 1980's.
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\nBiotic changes also appear to be influencing species assemblages and density within the lake. The idea of a trophic cascade is more simply stated as changes that occur to species at one trophic level has an impact (positive or negative) to species in the next trophic level, which then in turn impacts species in the next trophic level until it has reverberated throughout all trophic levels. Trophic cascades can be top-down or bottom-up. Top-down cascades tend to begin with a change in the apex predator and work their way down to autotrophs, while bottom-up cascades will typically begin with the autotrophs and work upwards to the apex predators.
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\nWhat the data indicate are that autotrophs have declined, likely due to decreases in nutrient levels and consumption by Zebra Mussels. Zooplankton have also become depleted, likely due to the declines in the autotroph trophic level, along with predation by Spiny Water Flea, and competition with Zebra Mussels. The third trophic level consisting of the forage fish also appears to have decreased as an overall group, which in turn has caused an overall decrease in the apex predators, which still mainly consists of Walleye. These metrics are much more consistent with changes that would be predicted to occur due to declines in the lower portions of the food web.
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Sampling Programs
\nMille Lacs Lake is one of ten lakes in Minnesota's Large Like Program. These lakes have annual sampling of the fish populations, and frequent creel surveys. Specific to Mille Lacs Lake, sampling programs focusing on Walleye, Yellow Perch, Smallmouth Bass, and Northern Pike are conducted annually. Additionally, we have annual summer and winter creel surveys to document angler use and fish harvest.
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\nWalleye
\nWalleye management on Mille Lacs Lake is conducted cooperatively with the Tribes signatory to the Treaty of 1837. A safe harvest level for Walleye is determined annually and is based on information collected through various sampling programs. For the 2024 fishing year (December 2023 through November 2024) the safe harvest level was set at 157,500 pounds, which is a 10% decrease from 2023 and is based on a similar percentage decrease of the lake's fishable Walleye population over the same time period. The State fishery portion of the safe harvest level is 91,550 pounds. By agreement, neither the Tribal nor State fishery harvest may exceed their respective quota. Fishing regulations are selected that offer the maximum opportunity to participate in the fishery (minimize likelihood of closures) and to offer opportunity to harvest, when possible, while staying within the quota.
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\nDuring the fall of 2023 we began observing angler Walleye catch rates increasing to almost double what occurred in fall 2022. Walleye catch rates continued increasing to the highest ever observed during the winter of 2023-2024, resulting in a relatively high harvest of Walleye, at the same time we observed the lowest angler effort ever recorded. In fact, angler pressure decreased about 75% from the previous year, while Walleye catch rates had increased by more than 10-fold. The high angler catch rates were due, in part, to the low levels of forage, particularly age-0 Yellow Perch, which are the primary dietary item for Walleye in Mille Lacs. Low abundance of forage items has consistently been shown to increase Walleye angling success on Mille Lacs Lake. The increased winter catch rate suggests that spring fishing for Walleye will also be relatively high which often results in increased angler effort, though the timing of inclement weather patterns can impact angling pressure.
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\nAnglers should expect to catch Walleye ranging in size from 12 to 24-inches long due to above average numbers of fish from the 2021, 2017, and 2013-year classes. Anglers will also likely see good numbers of smaller Walleye around 8-10 inches from the 2022-year class. These fish were very abundant in the fall survey, and they were also commonly reported as being caught by winter anglers, likely because of the low forage levels. Fall electrofishing and fine-mesh forage gill net sampling indicated that age-0 Walleye lengths were the second lowest observed for both gears, further suggesting low forage fish levels and making it less likely that the 2023 year-class will survive their first winter.
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\nYellow Perch
\nYellow Perch from the 2020 through 2022-year classes were highly abundant in the fall survey nets with relatively strong numbers of 10-to-12-inch fish from the latter two year-classes. We have observed some anglers picking up these larger fish during the 2024 winter; however, catch rates remained relatively weak, overall. We expect additional fish from all three year-classes to continue to grow into the fishable stocks over summer.
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\nSmallmouth Bass
\nSmallmouth Bass are managed to provide a high-quality fishery, and they are the second most common fish species that anglers pursue on Mille Lacs Lake. Current Mille Lacs regulations require anglers to release Smallmouth Bass longer than 17-inches. Spawning Smallmouth Bass are usually sampled during late May/early June using electrofishing gear. This is a sampling technique that allows fish to be released unharmed after they have their length measured. However, Smallmouth Bass were not sampled in the spring of 2023 due to effort instead being directed toward a Walleye mark-recapture population estimate that occurs every five years, which overlapped the time when spawning bass would have been available for spring sampling. Smallmouth Bass were still sampled in the annual fall gill nets, which are set in the latter half of September. Although the gill nets are not particularly efficient at sampling bass over 15 inches, we did observe several fish from 16 to just under 21 inches, indicating that we continue to maintain a high-quality population that appears to be still increasing in Mille Lacs.
\n
\nNorthern Pike
\nLike Smallmouth Bass, Northern Pike are managed to provide a high-quality fishery. Pike are managed with a 30-inch maximum size limit. Northern Pike are sampled in the spring, during spawning, using trap nets. Sampling fish with trap nets allows us to release the fish unharmed after we collect length and sex. A mark-recapture estimate was performed in spring 2023, which occurs every five years in conjunction with the Walleye population estimate. This meant increased effort was expended tagging Northern Pike and we examined just under 2,000 fish, despite heavy spring melt adversely impacting our ability to sample the stream spawning fish. We have found that very few male pike grow longer than 30-inches, while older females will grow to be longer than 40-inches, with the largest just over 45 inches. About 18% of the fish we sampled in the spring of 2023 were over 30-inches long, and 2% were trophy sized at over 40-inches in length.
\n
\nZebra Mussels, Rusty Crayfish, and Zooplankton
\nZebra mussels were first observed in Mille Lacs in 2005. Peak density occurred in 2012 after which abundance began decreasing. By 2017, densities had declined to about one half of their peak abundance, and for the last two years abundance has been at about a quarter to a third of their peak. Zooplankton abundance appeared to be slowly increasing the last several years; however, in 2022, the last year for which samples have been analyzed, we again saw densities decrease. Rusty crayfish eDNA from water samples taken in 2021 indicated that this aquatic invasive species was now in Mille Lacs. Visual confirmation occurred that same year when two specimens were observed near the Father Hennepin State Park swimming beach. In 2023 we observed our first specimen in DNR sampling gear (standard fall gill nets) in the southwest quadrant of the lake. Our population of Rusty Crayfish appears to still be relatively small; however, as the population continues to increase, we may see aquatic plant beds consumed throughout the lake by this invasive crustacean.
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AT PRESENT THE LAKES WALLEYE POPULATION IS DOMINA- TED BY THE 1984 AND 1988 YEAR CLASS WALLEYE. THE ABUNDANCE OF WALLEYE AGE CLASS XI AND OLDER HAS RETURNED TO MEAN LEVELS AFTER BEING WELL ABOVE AVERAGE FOR THE PAST 3 YEARS.
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trawling","species":"LGP","totalCatch":574},{"CPUE":"0.12","totalWeight":8645,"gearCount":16,"averageWeight":"9.53","quartileCount":"N/A","quartileWeight":"N/A","gear":"Standard trawling","species":"CAP","totalCatch":2},{"gear":"Standard trawling","totalCatch":169,"species":"JND","gearCount":16,"totalWeight":0,"CPUE":"10.56","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"0.00"},{"gearCount":3.85722222222222,"totalWeight":19,"CPUE":"68.96","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"0.00","gear":"Fall electrofishing","totalCatch":266,"species":"YEP"},{"totalCatch":2,"species":"BLG","gear":"Large-mesh gill nets","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"0.54","totalWeight":489,"gearCount":16,"CPUE":"0.12"},{"averageWeight":"0.26","quartileCount":"N/A","quartileWeight":"N/A","CPUE":"0.12","gearCount":16,"totalWeight":239,"species":"PMK","totalCatch":2,"gear":"Large-mesh gill nets"},{"totalCatch":9,"species":"BOF","gear":"Large-mesh gill nets","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"5.65","gearCount":16,"totalWeight":23051,"CPUE":"0.56"},{"totalWeight":1082,"gearCount":16,"CPUE":"0.25","quartileWeight":"N/A","averageWeight":"0.60","quartileCount":"N/A","gear":"Large-mesh gill nets","totalCatch":4,"species":"HSF"},{"CPUE":"0.62","totalWeight":2608,"gearCount":16,"quartileCount":"N/A","averageWeight":"0.57","quartileWeight":"N/A","gear":"Large-mesh gill nets","species":"BLC","totalCatch":10},{"totalCatch":2,"species":"RKB","gear":"Standard trawling","quartileWeight":"N/A","averageWeight":"0.00","quartileCount":"N/A","gearCount":16,"totalWeight":0,"CPUE":"0.12"},{"gear":"Standard trawling","species":"YEP","totalCatch":25034,"CPUE":"1564.62","totalWeight":8721,"gearCount":16,"averageWeight":"0.00","quartileCount":"N/A","quartileWeight":"N/A"},{"averageWeight":"8.18","quartileCount":"N/A","quartileWeight":"N/A","CPUE":"0.25","gearCount":16,"totalWeight":14842,"species":"NOP","totalCatch":4,"gear":"Standard trawling"},{"quartileWeight":"0.8-1.5","averageWeight":"1.54","quartileCount":"0.0-0.2","totalWeight":4186,"gearCount":52,"CPUE":"0.12","totalCatch":6,"species":"SMB","gear":"Standard gill nets"},{"gear":"Standard trawling","totalCatch":15,"species":"LMB","totalWeight":0,"gearCount":16,"CPUE":"0.94","quartileWeight":"N/A","averageWeight":"0.00","quartileCount":"N/A"},{"quartileWeight":"N/A","averageWeight":"0.80","quartileCount":"N/A","gearCount":16,"totalWeight":12262,"CPUE":"2.12","totalCatch":34,"species":"BRB","gear":"Large-mesh gill nets"},{"totalCatch":1,"species":"MUE","gear":"Standard gill nets","quartileWeight":"3.3-8.0","quartileCount":"0.0-0.1","averageWeight":"3.88","gearCount":52,"totalWeight":1760,"CPUE":"0.02"},{"totalWeight":19728,"gearCount":52,"CPUE":"0.31","quartileWeight":"1.6-2.1","averageWeight":"2.72","quartileCount":"0.8-2.4","gear":"Standard gill nets","totalCatch":16,"species":"WTS"},{"quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"0.00","totalWeight":0,"gearCount":16,"CPUE":"461.81","totalCatch":7389,"species":"SPO","gear":"Standard trawling"},{"CPUE":"12.44","gearCount":16,"totalWeight":352808,"averageWeight":"3.91","quartileCount":"N/A","quartileWeight":"N/A","gear":"Large-mesh gill nets","species":"WAE","totalCatch":199},{"totalCatch":3,"species":"SMB","gear":"Standard trawling","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"0.00","totalWeight":0,"gearCount":16,"CPUE":"0.19"},{"gear":"Standard gill nets","species":"TLC","totalCatch":59,"CPUE":"1.13","totalWeight":23543,"gearCount":52,"averageWeight":"0.88","quartileCount":"4.9-17.6","quartileWeight":"0.4-0.5"}],"narrative":"The walleye population appeared below average in the 2007 sampling. The inshore gill net catch rate, at half the long-term average, was the lowest observed. Below average catches were spread across most sizes of walleye, especially when compared to 2006. However, there was no good explanation as to why numbers decreased by so much. Furthermore, the walleye numbers were only seriously affected on the north shore. Trawling catches were average for fish older than age 1, which contradicted the abnormally low gill net catches on the north side. Ther are also conflicts between gears concerning the abundance of the 2006 year class. Nevertheless, the total weight per net in the inshore gill nets was the lowest observed since 1983, and pushed the fishery into \"condition 3\" according to the State harvest overage plan. This restricts State anglers to remaining within their allocation in 2008. A mark-recapture population estimate is planned for spring of 2008 to obtain a better estimate of walleye abundance.
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\nThe abundance of older yellow perch has declined as the 1996 year class has grown old and died off. The next strong year class was 2002, which contributed most of the large perch in 2007. An abundance of young-of-year yellow perch in 2007 will provide abundant forage in 2008, and is expected to moderate catch rates of walleye.
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\nRecent warm summers may be affecting the abundance of temperature sensitive species. Obvious declines in abundance have been observed for burbot and tullibee, while more subtle declines may be occurring for white sucker. On the other hand, species like smallmouth bass, are showing a gradual increase in abundance as warmer temperatures lead to more favorable environments for warmwater species. Increases in the abundance of largemouth bass and other centrarchids are expected, but most of these species are not sampled well.
\nTullibee numbers fell to the lowest observed in both inshore and offshore gill nets for the second consecutive year. If the tullibee population is suffering a permanent decline, many impacts may be felt by other species in the lake. First, lack of a medium to large forage species may be increasing predation pressures on young walleye, and may be contributing to the declining year class strengths. Second, lack of tullibee may also increase energy required to feed, and decrease the quality of the food, which may in turn reduce growth rates and maximum size of walleye. Similar concerns can be applied to northern pike and muskellunge as well, and could even be exacerbated by the reduction in white sucker as well. Many muskellunge anglers are fishing Mille Lacs Lake because of the potential for very large fish, possibly even a state record. This dynamic would certainly change if maximum sizes decrease in the future. Furthermore, future muskellunge stocking rates need to consider changes in forage abundance and quality.
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\nThe muskellunge genetics study has confirmed that natural reproduction contributes significantly to the muskellunge population. Natural recruits contribute at least 25% and perhaps 50% of the adults. Many of the naturally reproduced muskellunge are hybrids between different stocked strains. As hybridization between the strains continues, it is likely that the Mille Lacs muskellunge population will carry genes from both of the Wisconsin strains for many generations. The continued presence of shoepack genes in some of the hybrid muskellunge was also a surprise, and demonstrates that that strain has persisted on natural reproduction alone for almost 30 years. In the spring of 2008, muskellunge will be sampled during spawning. Naturally reproduced fish from the four year stocking gap from 2000-2003 will be between 5 and 8 years old, which is a good compromise between being fully recruited to the spawning stock and being young enough for decent age assignment.
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\nThe discovery of zebra mussels in Mille Lacs Lake in 2005 represents a serious threat to Mille Lacs Lake and many others lakes to which zebra mussels from Mille Lacs Lake could be transported. Future effects to native invertebrates, walleye spawning areas, swimming beaches, the bait industry, and the local economy are unknown. In 2007, several new developments were observed. First, most of the zebra mussels found were small (less than 20 mm). Second, this was the first year that zebra mussels were collected in close enough proximity to confirm the ability to reproduce naturally. Third, zebra mussels were confirmed in the south end of the lake at three different sites. Fourth, veligers were collected in plankton tows. And finally, zebra mussels collected off a cinder block used to hold a data logger represented the first report of confirmed colonization of a temporary object. All of these developments support the classification of Mille Lacs Lake as \"infested\", and are evidence for significant natural reproduction.
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The Mille Lacs Lake game fish community is primarily composed of walleye, yellow perch, northern pike, muskellunge, and smallmouth bass. Other game fish include largemouth bass, bluegill, pumpkinseed and black crappie. Common minnow species include spottail shiner and mimic shiner. Invasive animal species include common carp, zebra mussel, Chinese mystery-snail, banded mystery-snail, and spiny water flea. Curlyleaf pondweed and Eurasian watermilfoil are well established in the lake.
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\nCreel Survey
\nFishing effort for the 2011-2012 winter season was 1.63 million angler-hours (ang-hrs), about 7% below average. Open water 2012 fishing effort was 1.42 million ang-hrs, which is average. Walleye harvest declined slightly from 2011 levels to 173,900 lbs. Total kill was 310,000 lb, a 35% increase over 2011. Anglers released an additional 1,875,000 lb of walleye, which was almost a 125% increase over 2011. Most of the harvested walleye were age 3 and age 4.
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\nAnglers harvested 6,800 lb of northern pike, and released 102,000 lb. Total kill for pike was 11,000 lb.
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\nYellow perch harvest was 34,800 lb. Tullibee harvest was 3,250 lb, Anglers caught 66,500 smallmouth bass in 2012, which was the highest ever observed for Mille Lacs Lake.
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\nFall Assessment
\nWalleye catch per effort (CPE) in the inshore gillnets was 4.8 fish/net and 10.7 lb/net, the lowest ever observed. In offshore nets, walleye CPE was 9.9 fish/net and 25.4 lb/net, which are also the lowest observed. The CPE of walleye longer than 20 inches increased slightly in the offshore nets, and remains at a moderate level of five per net. In the inshore nets, CPE of larger walleye decreased for the second consecutive year to about 2 per net, which is well below peak values of close to 5 per net from 2000-2006. As observed in recent years, the 2000, 2001, 2004, 2009 and now the 2010 year classes are poorly represented in the gill nets, while 2005 through 2008 appear average. Early indications from electro-fishing suggest that the 2011 year may be low and the 2012 year class has the potential to be above average. The proportion of mature walleyes that were male in inshore gill nets decreased to the second lowest observed at 37%. The catch-per-effort of mature males in both the inshore and offshore nets decreased to the lowest levels observed. The number of mature female walleye in the inshore nets decreased in 2012, and is approaching the lowest level observed. Mature females increased slightly in the offshore nets where their numbers continue to remain relatively stable since these nets were first utilized in 1998. Walleye growth was below average for female walleye and the lowest observed for larger males. Growth was average for males ages 1-3. Walleye condition was below average at all sizes, and was the lowest observed for walleye greater than 20 inches.
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\nNorthern pike declined in the inshore nets for a second consecutive year to a CPE of 1.2 fish/net. Similarly, the northern pike catch in the 16 specialized northern pike gill nets declined for the second consecutive year to a CPE of 6.1 fish/net. Northern pike catch in the inshore nets went from a historical high in 2010 to below average in 2012. The specialized pike nets that were first set in 2007 went from the highest observed CPE in 2010 to the lowest observed in 2011 and again declined in 2012. The median weight of northern pike was below median at 4.4 lbs. Inshore nets sampled 10 year classes of northern pike, with an unusual observation of ten age 0 fish, which were all caught in a single net. Large pike (>28 inches) had generally been increasing since special regulations were implemented in 1998. In 2012, large pike numbers decreased by almost 50% and were well below average. Approximately 30% of the northern pike caught in the inshore nets were over 28 inches in length. Mature female pike weight in the inshore nets decreased 67%, from the 2010 historical high of 310 lbs to 102 lbs in 2012, which is the lowest weight observed since 2000. While gill net indices suggested a decrease in abundance, current population modeling suggests population biomass was still between 230,000 and 330,000 lbs, which is considerably higher than the average biomass from 1985-1997 of 147,000 lbs. Mark-recapture population estimates are planned for the spring of 2013, for both walleye and northern pike. These independent population estimates should help resolve some of the discrepancies observed between the gill net indices which, indicate sharp declines for these species, and the more robust model outputs that suggest the population decreases are more muted or non-existent.
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\nYellow perch CPE declined in the inshore gillnets to the lowest observed since 1989 at 19 fish/net and 5.7 lb/net. Gill net CPE of perch larger than 9 in had remained stable for the last five years, but dropped by about 50% to around 7 fish/net in 2012. In the offshore nets, perch CPE also declined by about 50% to a CPE of 17.9 fish/net and 6.3 lb/net.
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\nTullibee CPE declined sharply by about 88% to 0.2 fish/net and 0.2 lb/net in the inshore nets and increased about 30% to a relatively high level of 20.1 fish/net and 21.8 lb/net in the offshore nets. Sixty-six percent of the tullibee caught in the gill nets were four years old, with no other strong year classes apparent in the population. The difference in magnitude between the inshore and offshore catches, in 2012, may reflect a diminished population that is no longer over-flowing into the less desirable habitat of the near shore region, or it may represent a behavioral shift due to other environmental factors.
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\nOther species were also caught in standard gill nets, generally in low numbers. Burbot continue to exhibit declining numbers, and are now only occasionally observed in the assessment nets. Rock bass increased slightly to above average levels in 2012. Smallmouth bass catch remained at 1.0 fish/net in 2012, the third highest level observed in the inshore gill nets. Trends over the last decade show an increasing smallmouth bass population in the lake.
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\nThe forage gill nets showed weak numbers of tullibee and yellow perch at all ages. Age 1 and age 2 tullibee were at moderate levels. Age 0 spottail shiners were relatively high, while age 1+ spottails were moderate to low. Bluntnose minnows were absent in the four panel forage gill nets and observed at trace levels in the six panel nets. The CPE of YOY and age 1 yellow perch in the trawl were among the lowest observed, however, it appears that aquatic invasive species may be interfering with trawl catches, particularly in the Wealthwood area. The size of YOY perch caught in the trawl was the highest ever observed at 3.2 inches, however, the size of YOY perch observed while fall electrofishing was much closer to typical expected average length at 2.8 inches. Reduced forage levels help explain the low condition observed in fall walleyes and suggest an increased propensity for a strong walleye bite for recreational anglers until forage stocks are replenished in early summer. While this was not reflected in the fall angler catch rates, which were low, it was realized in the winter 2012-13 fishing season, which experienced very high angler catch rates of primarily large walleye.
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\nInvasive Species
\nZebra mussel density increased slightly to 1270/ft2, which was about 1.3 times higher than in 2011, and represents the lowest amount of increase since zebra mussels were first observed in 2005. Veliger (larval zebra mussels) densities generally increased from 2011 levels, particularly from May through July. The 2012 peak levels were the second highest observed in the five years we have been performing veliger counts.
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\nSpiny water flea (Bythotrephes) was observed during each sampling period from May through September with the exception of the May samples. Peak density occurred in September and was 6.1 Bythotrephes per sample. Cursory spot checks of fish stomachs show that age 1+ tullibee and age 1+ yellow perch were consuming spiny water flea. The peak level of spiny water flea observed in 2012 was less than the peak levels observed the previous two years.
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\nMore detailed reports are available at http://www.dnr.state.mn.us/areas/fisheries/aitkin/index.html
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Sampling Programs
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\nMille Lacs Lake is one of ten lakes in Minnesota's Large Like Program. These lakes have annual sampling of the fish populations, and frequent creel surveys. Specific to Mille Lacs Lake, sampling programs focusing on Walleye, Yellow Perch, Smallmouth Bass, and Northern Pike are conducted annually. Additionally, we have annual summer and winter creel surveys to document angler use and fish harvest.
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\nWalleye
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\nWalleye management on Mille Lacs Lake is conducted cooperatively with the Tribes signatory to the Treaty of 1837. A safe harvest level for Walleye is determined annually and is based on information collected through various sampling programs. For the 2023 fishing year (December 2022 through November 2023) the safe harvest level was set at 175,000 pounds, which is the highest safe harvest level since 2013. The State fishery portion of the safe harvest level is 100,300 pounds. By agreement, neither the Tribal nor State fishery harvest may exceed their respective quota. Fishing regulations are selected that offer the maximum opportunity to participate in the fishery (minimize likelihood of closures) and to offer opportunity to harvest, while staying within the quota.
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\nWalleye fishing success was slow during the winter of 2022-2023, resulting in very low harvest. The slow fishing was most likely due to a relatively high abundance of small Yellow Perch, which are the primary forage item for Walleye. High abundance of forage items has consistently been shown to reduce angling success on Mille Lacs Lake, as well as other lakes. The slow winter fishing success suggests that spring fishing will also be slow, though weather patterns will also have an impact.
\nThe most common sizes of Walleye that anglers should expect to catch range from 17 to 22-inches long. The majority of the Walleye in this length range are from the strong 2013 and 2017 year classes. Anglers should also see good number of small Walleye, in the 8-inch range, from the 2022 year class. These fish were very abundant in the fall survey, and they were also commonly reported as being caught by winter anglers. At this point it is not clear if the 2022 year class will continue to persist through future years.
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\nYellow Perch
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\nYellow Perch from the 2020 and 2021 year classes were highly abundant in the fall survey nets. The largest fish from these year classes were just over 8-inches long. Winter anglers reported catching quite a few Yellow Perch in this size range but did not keep many, as they were judged to be too small. By the winter of 2023-2024 many of the perch from these year classes will have grown to be of a size anglers would prefer to harvest.
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\nSmallmouth Bass
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\nSmallmouth Bass are managed to provide a high-quality fishery, and they are the second most common fish species that anglers pursue on Mille Lacs Lake. Current Mille Lacs regulations require anglers to release Smallmouth Bass longer than 17-inches. Spawning Smallmouth Bass are sampled in the spring using electrofishing gear. This is a sampling technique that allows fish to be released unharmed after they have their length measured. Three hundred-twenty-four bass were sampled in spring, 2022, with about one half of those longer than the 17-inch maximum size limit, and 9 longer than 20-inches. On Mille Lacs Lake it takes about 9 years for a bass to reach 20-inches in length. The overall size distribution was very similar to what was found in previous years.
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\nNorthern Pike
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\nLike Smallmouth Bass, Northern Pike are managed to provide a high-quality fishery. Pike are managed with a 30-inch maximum size limit. Northern Pike are sampled in the spring, on their spawning run, using trap nets. Sampling fish with trap nets allows us to release the fish unharmed after we collect length and sex. We have found that very few male pike grow longer than 30-inches, while females will grow to be longer than 40-inches. Sampling has found that about 14% of the adult females we sample are over 36-inches long, and 4% are over 40-inches in length. This describes a high-quality Northern Pike size structure.
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\nZebra Mussels
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\nZebra mussels were first observed in Mille Lacs in 2005. Peak density occurred in 2012 after which abundance began decreasing. By 2017 abundance had declined to about one half of their peak abundance, and for the last two years abundance has been at about one third of their peak abundance. Zooplankton abundance appears to be slowly increasing the last several years which may be related to the declining zebra mussel abundance.
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Electrofishing
\n\tFall electrofishing for Walleye is typically performed to determine reproductive success by evaluating the number of age 0 fish observed and how well they grew throughout the summer. We also evaluate potential strong year classes and annual survival of smaller Walleye by sampling the age 1 Walleye. The 2021 average catch rate for all stations combined for age 0 Walleye was just above the long-term median of 140.0 fish/hr, indicating no issues with spring reproduction, although it's relatively rare to sample low numbers of age 0 Walleye in the fall on Mille Lacs. Similarly, average catch rate for age 1 Walleye was 15.0 fish/hr, which is about a 60% increase over the median of 9.4 Walleye/hr, potentially indicating a future strong year class. Lengths in the electrofishing samples ranged from 3.5 inches to 8.4 inches for age 0 Walleye and from 8.7 inches to 12.4 inches for age 1 Walleye. Median length of age 0 Walleye was 5.9 inches, which is above the long-term median of 5.7 inches. Likewise, the median length of age 1 Walleye was 9.6 inches, which is also above the median of 9.1 inches, indicating a sufficiently long growing season with adequate forage.
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\n\tElectrofishing age 0 catch rates do not predict age 1 catch rates the following year on Mille Lacs, suggesting that the number of Walleye available at age 0 at current levels has little bearing on the number of Walleye that will be available as age 1 fish. This implies that current Walleye recruitment in Mille Lacs is not at a level where there is a density-dependent relationship with spawning stock and that something beyond reproductive output is likely governing Walleye recruitment in this lake.
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\nForage Gill Nets
\n\tForage gill net catches of age 0 Walleye at 1.4 fish/net were below the median of 2.04 fish/net. This places the 2021 catches at the 38th percentile. We sampled no age 1 Walleye in the 2021 forage nets; however, with the largest mesh of this gear being 0.75 inch bar measure it not an efficient gear for the typical fish species found in Mille Lacs that are over eight inches in length. The forage gill nets will generally sample age 1 Walleye if there is a large cohort available (ex. 2013 and 2017 year classes), but the disparity between the number of fish from this cohort observed in the electrofishing versus the forage gill nets would seem to suggest that either the age 1 year class was mainly located in the near-shore regions (< 8 ft. depths) of the lake during early September or that fish weren't moving enough to be readily sampled in the passively fished gill nets.
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\n\tAge 0 Yellow perch were sampled at a moderate range of abundance, indicating that forage was available throughout the open-water period for all sizes of piscivores. Similarly, age 1 Yellow Perch were slightly below the annual median, which provides additional forage for the larger fish eating predators. Age 0 Tullibee can provide alternate forage if age 0 Yellow perch are in short supply and catches for this forage item were also sampled at a moderate level.
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\nStandard Fall Gill Nets
\n\tWalleye catch per effort (CPE) in the inshore gillnets dropped in both number and biomass with both values below the first quartile. The decrease in catch rate occurred mainly due to sampling less fish below 20 inches. The offshore net catch remained relatively stable from the previous year with biomass slightly increasing; however, catches remain below the first quartile. The walleye length frequency distribution shows that the 2013 year class continues to make up a prominent portion of the Walleye population (approximately 37%) and the 2017 year class has mostly recruited to the spawning stocks and makes up approximately 17% of the sampled fish. The 2017 year class fish span a length range from 14 inches through 19 inches, while 2013 year class Walleye span lengths from 17 inches through 23 inches. The 2014, 2015, and 2016 year classes were sampled near median level for their respective age classes, but all year classes after 2017 were sampled near the first quartile.
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\n\tWalleye condition, an indication of fish fatness, improved among medium and large Walleye (> 14\") and dropped slightly for smaller Walleye; however, while improved, condition across all sizes remains below the Mille Lacs standard for expected weight at length. Condition in the medium and larger sized Walleye is likely a result of the improved forage levels. The improved forage availability is also likely responsible for the reduced angler catch rates we've observed since the winter fishery and throughout the summer as sated Walleye are much less likely to take anglers offerings.
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\n\tYellow Perch CPE in both the inshore and offshore gill nets increased in 2021. Catch rates were above median in both sets of nets, while biomass was below median due to an abundance of age 1 fish that comprised over 70% of the catch for this species. The age 1 cohort ranged in size from 4.5 inches to 7.5 inches, which provides an excellent forage base for larger predators, but it will still take another couple of year's growth to become a size that would appeal to anglers. Yellow perch over 10 inches in length comprised just under 3% of the fish sampled for this species and while that number is diluted in part due to the current abundance of the age 1 cohort, all age classes beyond age 2 were sampled below median levels.
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\n\tTullibee CPE in the nearshore nets remains well below the first quartile and also dropped below the first quartile for the first time since 2013 in the offshore nets. Tullibee CPE, particularly in the offshore nets, has been exhibiting fairly regular periodic spikes at five to six year intervals. The last spike in Tullibee numbers occurred in 2015 and consisted mainly of age 1 fish (2014 year class). Since both males and females tend to reach maturity by age 2 and are capable of living beyond 9 years old, it seems unlikely that the periodicity in the spikes is related to the amount of adult fish available for spawning in the population. The majority of the fish observed in the 2021 gill nets were from the 2013 and 2014 year classes with limited recruitment apparent since those cohorts.
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\n\tNorthern Pike CPE in the inshore gill nets has been slowly increasing the last several years and is above median level in 2021. Mean weight of Northern Pike also increased and is at 5.6 lb, which is just below the 75th percentile, indicating excellent abundance of large fish.
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\n\tOther species were also caught in standard gill nets, generally in low numbers. White Sucker were observed at levels that were slightly below median in the inshore nets and offshore gill nets. Rock Bass indexes surpassed the 75th percentile in both the inshore nets and offshore nets. No Burbot were sampled in 2021, which is now a common occurrence in our fall sampling. Burbot have exhibited a declining trend in abundance since we began recording data on this species in 1979, likely due to increased and prolonged summer water temperatures. Due to continuing low burbot numbers in Mille Lacs a new regulation of catch-and-release has been enacted for this species.
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\n\tCatches of Smallmouth Bass were the highest observed in both inshore and offshore areas. Smallmouth Bass CPE in the gill nets is often more an index of smaller and medium sized fish as it appears that fish greater than fifteen inches tend to exhibit much reduced catchability in the gill nets. Most of the Smallmouth bass observed in the gill nets were between 13 inches to 18 inches, although we did sample a few specimens up through 21 inches in length.
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\n\tSpring spawn-oriented sampling generally provides better data on adult Smallmouth Bass as we use electrofishing to sample shallow spawning fish. Spring sampling began on 1 June, 2021 and continued through 10 June, 2021. Our sampling period was relatively short due to quickly increasing water temperatures that appeared to drive bass into deeper water where the electro-shocking boat was less effective. A relatively high proportion of fish sampled in 2021 were below 10 inches; however, 90% of the smaller fish were sampled over the last four days of the ten day sampling period, whereas over 85% of the Smallmouth bass over 18 inches were sampled during the first six days. Despite the temperature anomalies we still observed quality sized fish to 20.5 inches.
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\nAquatic Invasive Species/Zooplankton
\n\tZebra mussels were first observed in Mille Lacs in 2005. Peak density occurred in 2012 after which densities began decreasing steadily until about half in 2017 and then stabilizing at that level. The population now appears to have reached an equilibrium over the last several years, around which slight oscillations are being observed as the population now maintains itself near carrying capacity.
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\n\tVeligers are the planktonic motile immature stage of the adult Zebra mussels. Being planktonic we are able to sample the veligers in our normal zooplankton sampling tows. Peak veliger density in 2021 occurred in mid-June at a moderate level when compared to previous years and then dropped throughout the rest of summer to comparatively low levels.
\n
\n\tZooplankton samples were collected in 2021 throughout the open-water period using our normal sampling protocols; however, the samples were not processed due to a vacancy at the analyst position. 2020 samples were evaluated by a temporary employee with the results delivered in 2021. The 2020 samples continued to show an increasing trend in the aquatic invasive Bythotrephes (Spiny water flea) density and strong decreases in the native zooplankton community. While all functional groups declined in 2020 to some of the lowest levels observed, particularly noticeable by their absence where the small cladocerans and cyclopoids, which tend to be a preferred forage item for smaller fish throughout the lake. Both Spiny water flea and various forage fish species compete for small cladocerans and it appears that the Spiny water flea are reshaping the structure of the zooplankton community and are creating bottlenecks in the food web for those native species that would normally feed on the smaller cladocerans. As zooplankton eating fish grow larger they can actually prey upon the Spiny water flea; however, they first need to become large enough to get past the large tail spine that is present on this aquatic invasive. Unfortunately, the competition with Spiny water flea for the smaller zooplankton appears to compromise growth rates in these small fish making it more difficult to grow to a size where they can effectively prey on Bythotrephes. Further, reduced growth rates in the native prey species would also make them more susceptible to predators over longer periods of time which often further reduces their presence as adults.
\n
AT PRESENT THE LAKES WAE POPULATION IS DOMINATED BY THE 1984 AND 1988 YEAR CLASS WAE.
","surveySubType":"Population Assessment"},{"narrative":"AT THE PRESENT THE LAKES WAE POPULATION IS PREDOMINATED BY THE 1988 AND 1991 YEAR CLASS WAE. ADULT YEP ABUNDANCE DECLINED TO MODERATELY LOW LEVELS AFTER THE LAST TWO YEARS OF RECORD HIGH CATCHES IN THE ASSESSMENT NETS.
","surveySubType":"Population Assessment","surveyID":"113358","surveyType":"Standard Survey","headerInfo":{"id_date":"1992-06-22","wb_alt_name":"","wb_type":"Lake","wb_name":"Mille Lacs","survey_id":"113358","county":"Mille Lacs","wb_id":"48000200","survey_type":"Population Assessment"},"fishCatchSummaries":[{"species":"TLC","totalCatch":170,"gear":"Standard gill nets","quartileCount":"4.9-17.6","averageWeight":"0.46","quartileWeight":"0.4-0.5","CPUE":"5.31","gearCount":32,"totalWeight":78.5},{"totalCatch":16,"species":"BUB","gear":"Standard gill nets","quartileWeight":"1.1-2.1","quartileCount":"0.0-0.2","averageWeight":"1.16","gearCount":32,"totalWeight":18.5,"CPUE":"0.50"},{"gear":"Standard gill nets","totalCatch":37,"species":"NOP","gearCount":32,"totalWeight":227.9,"CPUE":"1.16","quartileWeight":"2.4-4.3","quartileCount":"0.9-4.3","averageWeight":"6.16"},{"totalCatch":13,"species":"BLC","gear":"Standard gill nets","quartileWeight":"0.2-0.5","quartileCount":"0.1-0.7","averageWeight":"0.48","gearCount":32,"totalWeight":6.2,"CPUE":"0.41"},{"quartileWeight":"1.6-2.1","averageWeight":"2.26","quartileCount":"0.8-2.4","totalWeight":29.4,"gearCount":32,"CPUE":"0.41","totalCatch":13,"species":"WTS","gear":"Standard gill nets"},{"totalWeight":16.3,"gearCount":32,"CPUE":"0.06","quartileWeight":"3.3-8.0","averageWeight":"8.15","quartileCount":"0.0-0.1","gear":"Standard gill nets","totalCatch":2,"species":"MUE"},{"CPUE":"16.25","totalWeight":881.5,"gearCount":32,"quartileCount":"3.3-14.8","averageWeight":"1.70","quartileWeight":"0.9-1.5","gear":"Standard gill nets","species":"WAE","totalCatch":520},{"gear":"Standard gill nets","totalCatch":1,"species":"CAP","gearCount":32,"totalWeight":23.3,"CPUE":"0.03","quartileWeight":"2.3-10.8","quartileCount":"0.0-2.3","averageWeight":"23.30"},{"totalWeight":5.1,"gearCount":32,"CPUE":"0.16","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"1.02","gear":"Standard gill nets","totalCatch":5,"species":"BLH"},{"gearCount":32,"totalWeight":166.8,"CPUE":"23.28","quartileWeight":"0.2-0.3","averageWeight":"0.22","quartileCount":"9.9-57.1","gear":"Standard gill nets","totalCatch":745,"species":"YEP"},{"quartileWeight":"0.3-0.6","averageWeight":"0.45","quartileCount":"0.1-1.1","totalWeight":13.1,"gearCount":32,"CPUE":"0.91","totalCatch":29,"species":"RKB","gear":"Standard gill nets"}],"lengths":{},"surveyDate":"1992-06-22"},{"surveyDate":"1999-09-10","fishCatchSummaries":[{"species":"TLC","totalCatch":126,"gear":"Standard gill nets","averageWeight":"0.51","quartileCount":"4.9-17.6","quartileWeight":"0.4-0.5","CPUE":"3.94","gearCount":32,"totalWeight":64.74},{"species":"BUB","totalCatch":2,"gear":"Standard gill nets","averageWeight":"1.14","quartileCount":"0.0-0.2","quartileWeight":"1.1-2.1","CPUE":"0.06","totalWeight":2.27,"gearCount":32},{"species":"BRB","totalCatch":1,"gear":"Standard gill nets","quartileCount":"0.1-0.6","averageWeight":"0.32","quartileWeight":"0.6-1.2","CPUE":"0.03","gearCount":32,"totalWeight":0.32},{"quartileWeight":"0.2-0.5","quartileCount":"0.1-0.7","averageWeight":"0.47","totalWeight":1.89,"gearCount":32,"CPUE":"0.12","totalCatch":4,"species":"BLC","gear":"Standard gill nets"},{"CPUE":"1.50","gearCount":32,"totalWeight":297.35,"quartileCount":"0.9-4.3","averageWeight":"6.19","quartileWeight":"2.4-4.3","gear":"Standard gill nets","species":"NOP","totalCatch":48},{"CPUE":"0.59","totalWeight":9.81,"gearCount":32,"averageWeight":"0.52","quartileCount":"0.0-4.7","quartileWeight":"0.4-1.0","gear":"Standard gill nets","species":"BLB","totalCatch":19},{"averageWeight":"2.02","quartileCount":"0.8-2.4","quartileWeight":"1.6-2.1","CPUE":"0.66","totalWeight":42.32,"gearCount":32,"species":"WTS","totalCatch":21,"gear":"Standard gill nets"},{"CPUE":"0.09","gearCount":32,"totalWeight":38.42,"quartileCount":"0.0-0.1","averageWeight":"12.81","quartileWeight":"3.3-8.0","gear":"Standard gill nets","species":"MUE","totalCatch":3},{"quartileWeight":"0.9-1.5","quartileCount":"3.3-14.8","averageWeight":"2.22","gearCount":32,"totalWeight":723.6,"CPUE":"10.19","totalCatch":326,"species":"WAE","gear":"Standard gill nets"},{"gear":"Standard gill nets","species":"PMK","totalCatch":2,"CPUE":"0.06","gearCount":32,"totalWeight":0.32,"quartileCount":"N/A","averageWeight":"0.16","quartileWeight":"N/A"},{"quartileCount":"0.0-0.2","averageWeight":"1.46","quartileWeight":"0.8-1.5","CPUE":"0.09","gearCount":32,"totalWeight":4.38,"species":"SMB","totalCatch":3,"gear":"Standard gill nets"},{"totalCatch":2,"species":"YEB","gear":"Standard gill nets","quartileWeight":"0.6-1.1","averageWeight":"0.41","quartileCount":"0.1-1.1","gearCount":32,"totalWeight":0.83,"CPUE":"0.06"},{"gear":"Standard gill nets","totalCatch":3297,"species":"YEP","totalWeight":656.04,"gearCount":32,"CPUE":"103.03","quartileWeight":"0.2-0.3","quartileCount":"9.9-57.1","averageWeight":"0.20"},{"totalCatch":16,"species":"RKB","gear":"Standard gill nets","quartileWeight":"0.3-0.6","quartileCount":"0.1-1.1","averageWeight":"0.42","gearCount":32,"totalWeight":6.68,"CPUE":"0.50"}],"lengths":{},"headerInfo":{"wb_type":"Lake","wb_name":"Mille Lacs","id_date":"1999-09-10","wb_alt_name":"","wb_id":"48000200","survey_type":"Population Assessment","survey_id":"113624","county":"Mille Lacs"},"surveyType":"Standard Survey","surveyID":"113624","surveySubType":"Population Assessment","narrative":"Mille Lacs Lake is one of the most popular walleye and perch fishing destinations in Minnesota, with over 3.5 million hours of fishing pressure in 1999. The walleye population appeared healthy with an unbroken string of fair to good year classes since 1991, and a high proportion of larger walleye. Walleye catches in assessment nets were low in 1999, but this was not entirely unexpected, since larger fish are not well sampled in gill nets. From an angler's perspective, the return of normal water clarity has translated to better daytime fishing, which resulted in relatively less effort at night.The yellow perch population also appeared healthy based on 1999 sampling. Numbers of perch sampled were much lower in 1999 than in 1998, but still very high for Mille Lacs. The decrease in 1999 was due in part to the very large 1996 year class outgrowing the smallest gill net mesh size. The 1996 year class was still well represented, and should be large enough to appeal to winter anglers in the winter of 2000/2001.Northern pike and muskellunge were not well sampled by standard methods in Mille Lacs. Although the gill net catch of northern pike was well above average, there were only 1.5/net. Most of these fish were caught along the north shore. Based on angler catch rates in the summer, both northern pike and muskellunge were doing well. Many angled pike were over 30 inches, and we received numerous reports of muskellunge over 50 inches. Larger pike may have resulted from increased survival due to the 26-36 inch protected slot. Special sampling was conducted for smallmouth bass in 1999. Growth rates were good, and 10% of the spawners were over 20 inches long. The 1991 through 1993 year classes were weak or absent. The summers of these years were cold, and reduced recruitment of bass and panfish were observed in many lakes throughout Minnesota. These poor year classes will reduce the numbers of large fish over the next several years. The size distribution should begin to recover around 2004, although full recovery cannot occur until the 1993 year class is about 16 years old in 2006.
"},{"lengths":{"TRP":{"minimum_length":2,"maximum_length":4,"fishCount":[[2,69],[3,29],[4,13]]},"NOP":{"maximum_length":39,"minimum_length":21,"fishCount":[[21,1],[23,2],[24,2],[25,3],[26,4],[27,3],[28,3],[29,3],[30,4],[31,5],[32,7],[33,4],[34,1],[36,4],[39,1]]},"SMB":{"fishCount":[[13,2],[14,1],[15,1],[18,1],[2,1],[3,1],[4,1],[5,1],[7,1],[1,19]],"minimum_length":1,"maximum_length":18},"YEB":{"maximum_length":10,"minimum_length":10,"fishCount":[[10,2]]},"YEP":{"fishCount":[[10,436],[11,126],[12,17],[3,5],[4,588],[5,1217],[6,215],[7,376],[8,568],[9,440],[1,617],[2,11381],[3,282]],"maximum_length":12,"minimum_length":1},"BLC":{"fishCount":[[2,155],[3,12],[10,4],[11,3],[5,62],[6,58],[7,1],[8,2],[9,2]],"maximum_length":11,"minimum_length":2},"RKB":{"minimum_length":4,"maximum_length":10,"fishCount":[[10,3],[4,1],[7,4],[8,8],[9,6]]},"MUE":{"minimum_length":45,"maximum_length":45,"fishCount":[[45,1]]},"TLC":{"maximum_length":16,"minimum_length":8,"fishCount":[[10,2],[11,8],[12,36],[13,18],[14,4],[15,1],[16,1],[8,5],[9,9]]},"WAE":{"fishCount":[[2,2],[3,46],[4,318],[5,1377],[6,2132],[7,479],[8,1],[10,121],[11,39],[12,21],[13,43],[14,31],[15,106],[16,133],[17,136],[18,78],[19,38],[20,39],[21,51],[22,58],[23,62],[24,62],[25,76],[26,62],[27,25],[28,5],[29,3],[7,7],[8,97],[9,202]],"minimum_length":2,"maximum_length":29},"BUB":{"maximum_length":18,"minimum_length":15,"fishCount":[[15,1],[18,1]]},"SPO":{"fishCount":[[2,1226],[3,2656],[4,204],[7,26]],"maximum_length":7,"minimum_length":2},"LMB":{"minimum_length":2,"maximum_length":3,"fishCount":[[2,14],[3,7]]},"CAP":{"fishCount":[[17,1],[23,1]],"maximum_length":23,"minimum_length":17},"WTS":{"minimum_length":3,"maximum_length":18,"fishCount":[[3,2],[4,52],[5,5],[10,1],[11,1],[13,1],[15,2],[16,5],[17,1],[18,3],[5,1]]},"MMS":{"maximum_length":2,"minimum_length":1,"fishCount":[[1,833],[2,355]]},"BLG":{"maximum_length":1,"minimum_length":1,"fishCount":[[1,267]]},"LGP":{"fishCount":[[1,7],[2,14],[3,13]],"maximum_length":3,"minimum_length":1},"JND":{"fishCount":[[2,29]],"minimum_length":2,"maximum_length":2}},"fishCatchSummaries":[{"gear":"Special gill nets","totalCatch":1,"species":"CAP","totalWeight":3372,"gearCount":24,"CPUE":"0.04","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"7.43"},{"totalCatch":2,"species":"YEB","gear":"Standard gill nets","quartileWeight":"0.6-1.1","averageWeight":"0.66","quartileCount":"0.1-1.1","gearCount":52,"totalWeight":596,"CPUE":"0.04"},{"gear":"Fall electrofishing","totalCatch":2,"species":"SMB","totalWeight":9,"gearCount":3.98111111111111,"CPUE":"0.50","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"0.01"},{"gearCount":52,"totalWeight":102002,"CPUE":"0.69","quartileWeight":"2.4-4.3","quartileCount":"0.9-4.3","averageWeight":"6.25","gear":"Standard gill nets","totalCatch":36,"species":"NOP"},{"CPUE":"0.30","totalWeight":14776,"gearCount":20,"quartileCount":"N/A","averageWeight":"5.43","quartileWeight":"N/A","gear":"Standard trawling","species":"NOP","totalCatch":6},{"gear":"Fall 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nets"},{"totalWeight":0,"gearCount":20,"CPUE":"1.65","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"0.00","gear":"Standard trawling","totalCatch":33,"species":"LGP"},{"totalCatch":168,"species":"WAE","gear":"Special gill nets","quartileWeight":"N/A","averageWeight":"5.69","quartileCount":"N/A","gearCount":24,"totalWeight":433928,"CPUE":"7.00"},{"quartileWeight":"N/A","averageWeight":"0.00","quartileCount":"N/A","totalWeight":57,"gearCount":3.98111111111111,"CPUE":"51.74","totalCatch":206,"species":"YEP","gear":"Fall electrofishing"},{"gear":"Standard gill nets","totalCatch":5,"species":"SMB","gearCount":52,"totalWeight":3078,"CPUE":"0.10","quartileWeight":"0.8-1.5","averageWeight":"1.36","quartileCount":"0.0-0.2"},{"gearCount":20,"totalWeight":248,"CPUE":"5.55","quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"0.00","gear":"Standard trawling","totalCatch":111,"species":"TRP"},{"averageWeight":"0.01","quartileCount":"N/A","quartileWeight":"N/A","CPUE":"1.05","gearCount":20,"totalWeight":106,"species":"SMB","totalCatch":21,"gear":"Standard trawling"},{"gear":"Standard gill nets","totalCatch":1518,"species":"WAE","gearCount":52,"totalWeight":896166,"CPUE":"29.19","quartileWeight":"0.9-1.5","averageWeight":"1.30","quartileCount":"3.3-14.8"},{"gear":"Standard trawling","totalCatch":1499,"species":"WAE","gearCount":20,"totalWeight":146317,"CPUE":"74.95","quartileWeight":"N/A","averageWeight":"0.22","quartileCount":"N/A"},{"totalWeight":0,"gearCount":20,"CPUE":"1.05","quartileWeight":"N/A","averageWeight":"0.00","quartileCount":"N/A","gear":"Standard trawling","totalCatch":21,"species":"LMB"},{"quartileWeight":"N/A","quartileCount":"N/A","averageWeight":"0.00","gearCount":20,"totalWeight":0,"CPUE":"13.35","totalCatch":267,"species":"BLG","gear":"Standard trawling"},{"gear":"Standard gill nets","species":"TLC","totalCatch":84,"CPUE":"1.62","gearCount":52,"totalWeight":29833,"averageWeight":"0.78","quartileCount":"4.9-17.6","quartileWeight":"0.4-0.5"},{"CPUE":"1.12","totalWeight":5964,"gearCount":52,"averageWeight":"0.23","quartileCount":"0.1-0.7","quartileWeight":"0.2-0.5","gear":"Standard gill nets","species":"BLC","totalCatch":58},{"gear":"Standard gill nets","totalCatch":15,"species":"WTS","gearCount":52,"totalWeight":11968,"CPUE":"0.29","quartileWeight":"1.6-2.1","averageWeight":"1.76","quartileCount":"0.8-2.4"},{"totalWeight":62,"gearCount":20,"CPUE":"2.95","quartileWeight":"N/A","averageWeight":"0.00","quartileCount":"N/A","gear":"Standard trawling","totalCatch":59,"species":"WTS"},{"CPUE":"12.05","gearCount":20,"totalWeight":105,"averageWeight":"0.00","quartileCount":"N/A","quartileWeight":"N/A","gear":"Standard trawling","species":"BLC","totalCatch":241},{"quartileWeight":"0.2-0.3","averageWeight":"0.30","quartileCount":"9.9-57.1","totalWeight":356560,"gearCount":52,"CPUE":"50.02","totalCatch":2601,"species":"YEP","gear":"Standard gill nets"},{"gear":"Standard gill nets","totalCatch":2,"species":"BUB","totalWeight":1094,"gearCount":52,"CPUE":"0.04","quartileWeight":"1.1-2.1","averageWeight":"1.21","quartileCount":"0.0-0.2"},{"species":"YEP","totalCatch":13460,"gear":"Standard trawling","averageWeight":"0.00","quartileCount":"N/A","quartileWeight":"N/A","CPUE":"673.00","totalWeight":19977,"gearCount":20},{"gearCount":52,"totalWeight":10842,"CPUE":"0.02","quartileWeight":"3.3-8.0","quartileCount":"0.0-0.1","averageWeight":"23.90","gear":"Standard gill nets","totalCatch":1,"species":"MUE"},{"gear":"Standard trawling","species":"JND","totalCatch":29,"CPUE":"1.45","totalWeight":0,"gearCount":20,"averageWeight":"0.00","quartileCount":"N/A","quartileWeight":"N/A"},{"gear":"Standard trawling","totalCatch":1188,"species":"MMS","gearCount":20,"totalWeight":2,"CPUE":"59.40","quartileWeight":"N/A","averageWeight":"0.00","quartileCount":"N/A"},{"quartileCount":"N/A","averageWeight":"0.00","quartileWeight":"N/A","CPUE":"0.25","gearCount":3.98111111111111,"totalWeight":0,"species":"LGP","totalCatch":1,"gear":"Fall electrofishing"},{"totalCatch":5,"species":"TPM","gear":"Standard trawling","quartileWeight":"N/A","averageWeight":"0.00","quartileCount":"N/A","gearCount":20,"totalWeight":0,"CPUE":"0.25"},{"gear":"Special gill nets","species":"NOP","totalCatch":5,"CPUE":"0.21","totalWeight":24665,"gearCount":24,"quartileCount":"N/A","averageWeight":"10.88","quartileWeight":"N/A"}],"surveyDate":"2006-09-05","surveyID":"660623040426000","surveyType":"Standard Survey","headerInfo":{"wb_name":"Mille Lacs","wb_type":"Lake","wb_alt_name":"","id_date":"2006-09-05","wb_id":"48000200","survey_type":"Large Lake Survey","county":"Mille Lacs","survey_id":"660623040426000"},"narrative":" The walleye population continued to look healthy in 2006. The inshore gill net catch rate was the highest observed since 1991, caused by an extremely high catch of YOY walleye, coupled with higher than average catches of walleye over 20 inches. The 2002 and 2003 year classes were not as strong as expected in the inshore gill nets, but were abundant in the offshore nets. Offshore gill nets had higher catches of walleye for all year classes age 4 or less, while catches of older fish were about the same in inshore and offshore nets.
\n Walleye condition was below average for medium and large walleye, and about average for small walleye. This may have been the result of intraspecific competition, spreading an average amount of yellow perch among higher than average numbers of big and little walleye. However, the YOY walleye were among the largest ever observed in trawling and electrofishing, suggesting an abundance of food, at least for small fish.
\n Tullibee numbers fell to the lowest observed in both inshore and offshore gill nets. After a gradual but severe decline that fell to less than one tullibee per net in 2002, tullibee catches in the inshore nets increased to 11 per net in 2005. However, warm temperatures led to a severe tullibee summerkill. Many shoreland owners called to report tullibee washing up on shore at about one fish per foot of shoreline. While offshore nets still caught more tullibee than inshore nets, this was the first year that the offshore catch rate was less than five tullibee per net.
\n The 2006 catches of YOY yellow perch in the trawl indicated an average yellow perch year class. Mean length of yellow perch was slightly below average. The average perch abundance coupled with low numbers of tullibee and high walleye populations may lead to above average catch rates in 2007. High numbers of age 3 and 4 yellow perch in the gill nets suggest that yellow perch could provide decent fishing during the winter of 2007.
\n Northern pike numbers decreased slightly in the gill nets due to poor recruitment in recent years. Northern pike tagging studies were conducted in 2005 and 2006 to provide mark-recapture population estimates. In 2006, estimates ranged from 39,000 to 45,000 northern pike, depending on the methods used. Population estimates in 2006 were up to 17% less than in 2005, although the decreases were not statistically significant.
\n Of 200 spawning muskellunge sampled in the fall, 12% were longer than 50 inches. The largest muskellunge observed was about 54 inches long.
\n The discovery of zebra mussels in Mille Lacs Lake in 2005 represents a serious threat to Mille Lacs Lake and many others lakes to which zebra mussels from Mille Lacs Lake could be transported. Zebra mussels are capable of obtaining extremely high densities. Future impacts to native invertebrates, walleye spawning areas, swimming beaches, the bait industry, and the local economy in general are not known. To date, 13 of the 14 zebra mussels found in Mille Lacs have been on the north side of the lake, suggesting that any breeding populations are in the north and not widespread. However, all of the mussels found so far have been isolated and therefore unable to breed. Monitoring will continue at 20 permanent transects. Additional transects will also be used to try to find a breeding population. Zebra mussel monitoring may also play an important role in the early detection of other possible exotics such as rusty crayfish.
\n The ecological impact of Chinese mystery-snails is not fully known, but is apparently presumed small. However, the snail is a nuisance to anglers and lakeshore property owners. The high abundance of snails on the bottom results in frequent snagging by anglers fishing in the northeast portion of Mille Lacs Lake. Range and densities will be monitored occassionally to determine if this species is expanding in Mille Lacs Lake.
\n
The Mille Lacs Lake game fish community is primarily composed of Walleye, Yellow Perch, Northern Pike, Muskellunge, Tullibee, and Smallmouth Bass. Other game fish include Largemouth Bass, Bluegill, Pumpkinseed and Black Crappie. Common minnow species include Spottail Shiner and Mimic Shiner. Invasive animal species include Common Carp, Zebra Mussel, Chinese Mystery-snail, Banded Mystery-snail, and Spiny Water Flea. Curlyleaf Pondweed and Eurasian Watermilfoil are also well established in the lake.
\n
\nCreel Survey (December 1, 2016 to November 30, 2017)
\nCreel survey is the tool through which we estimate angler use and harvest of various fish species on Mille Lacs Lake. On Mille Lacs Lake, creel surveys have been conducted for both the summer and winter fisheries, and have been annual since 1983.
\n
\nFishing effort for the 2016-2017 winter season was 2,245,800 angler-hours (ang-hrs), about 30% above the 34 year average. An additional 10,200 angler-hours were observed during the late-ice creel, which ran for 21 days from February 27, 2017 through March 19, 2017. Ice fishing pressure increased from the previous year due to decent ice conditions that allowed anglers to access the lake by mid-December, along with the continuation of an exceptionally strong walleye bite that had begun the previous year.
\n
\nOpen water 2017 fishing effort was approximately 635,700 ang-hrs, which was about 53% below the 34 year average and the fourth lowest observed. Open water night effort was the lowest observed, due to an extended night closure that was in place through the open water season. Open water day pressure was below median level throughout all periods of the summer, most likely due to catch-and-release Walleye regulations and a mid-summer and early September Walleye closure in an attempt to stay below the 44,800 lb State allocation.
\nWalleye harvest, for the entire 2017 fishing season, was the fourth lowest observed at around 13,000 lbs with harvest only allowed during winter under an 19\"-21\" harvest slot. Total summer and winter kill, which includes hooking mortality, was slightly over 54,000 lbs. Anglers realized an exceptional Walleye catch rate throughout the entire year and released an additional 1,143,750 lb of Walleye. The winter Walleye catch rate was the third highest observed, while summer walleye targeted catch rates were the highest observed.
\n
\nAnglers harvested almost 22,000 lb of Northern Pike, which was almost equally split between the summer and winter fisheries. An additional 86,500 lb of Northern Pike were released, which created a hooking mortality estimate of about 3,850 lb and a total kill of 25,700 lbs. The total catch of Northern Pike in 2017 was the third highest observed in the last two decades.
\n
\nYellow Perch harvest was extremely low at 3,800 lb, which was the second lowest observed. Similarly, Tullibee harvest was also low at around 4,100 lb. Anglers caught approximately 128,000 Smallmouth Bass in 2017, which was the second highest ever observed for Mille Lacs. Slightly over 900 Smallmouth were harvested. In 2017, targeted effort for Smallmouth Bass was the highest observed. Smallmouth Bass targeted pressure has been increasing strongly since 2013, and now makes up about 40% of the open water effort.
\n
\nFall Assessment
\nThe fall gill net sampling on Mille Lacs Lake is our most important tool for assessing the health and abundance of the fish populations in the lake. The survey has been conducted annually since 1983, and intermittently for several years prior to that. The survey was originally conducted with 32 standard gill nets, but additional nets were added in the late 1990s and early 2000s to mitigate sampling deficiencies, mainly in the offshore regions of the lake. Currently we sample the lake using 32 standard gill nets set in the near-shore areas, an additional 20 standard gill nets in the off-shore portions of the lake, 25 specialized forage gill nets randomly located throughout the lake, and 16 specialized Northern Pike gill nets located in shallow, weedy areas around the periphery of the lake.
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\n Walleye catch per effort (CPE) in the inshore gillnets was 12.8 fish/net and 20.5 lb/net, and. 12.8 fish/net and 23.9 lb/net in the offshore nets. The Walleye catch rate increased from the previous year in both sets of nets to where the inshore catch was above median, while the Walleye catch in the offshore nets remained below the 25th percentile. The bulk of the Walleye catch came from the 2013 year class with only age 4 Walleye being observed at above median levels in the gill nets. The CPE of Walleye longer than 20 inches in the inshore nets did not change from the previous year, but remained the second lowest observed. The same metric decreased 10% in the offshore nets to the lowest on record. The CPE of mature males increased slightly in 2017, partially due to continued increased selectivity of the strong 2013 year class; however, mature male CPE remains at a relatively low level. Mature female CPE more than doubled from near the lowest observed in 2016 to slightly above average in 2017 due to maturation of most of the females in the 2013 year class.
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\nFor the past several years, forage items that Walleye prefer to feed on have been at relatively low abundance. This has resulted in very high angler catch rates, and skinny Walleye. Walleye condition (plumpness) on fish greater than 20 inches decreased to the second lowest observed, while medium and small sized walleye showed an improvement in condition but were still below average weight. The gradient in robustness among different sized Walleye suggests that smaller sized forage became available in the latter part of the 2017 summer and that larger Walleye had not yet recovered from their low condition state from the previous fall. Further, we would also suspect that larger walleye were biting much more strongly over the open water period, due to their reduced condition, than what would be proportionate to their availability in the population. Fall forage sampling confirmed that age 0 Yellow Perch and age 0 Tullibee were available in moderate-high numbers and that Walleye catch rates were likely to decrease for the upcoming 2018 ice fishing season as Walleye continued to find abundant forage.
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\nNorthern Pike CPE in the inshore nets decreased from 2016 by 45% at 0.88 fish/net, which is a drop from above median in 2016 to below the 25th quartile in 2017. Almost 70% of the fish were from the 2013 and 2014 year classes, which made up the majority of fish less than 28 inches. Fish greater than 28 inches also showed a strong decrease, dropping by over 65% to almost half the median. There were no age 0 or age 1 Northern Pike caught in the inshore nets, which suggests abundance will likely be low for the next couple of years. The Northern Pike catch in the 16 specialized Northern Pike gill nets decreased for the third year in a row to a CPE of 5.3 fish/net and 29.1 lb/net, which are the lowest observed.
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\nYellow Perch CPE showed little change from the previous year in the inshore nets and are below the 25th quartile at 20.5/net and 3.9 lb/net. Gill net CPE of perch larger than 9 inches decreased to 2.4 fish/net, which is the fourth lowest observed since 1985. Yellow Perch CPE in the offshore nets continues to remain low at 12.4/net and 3.7 lb/net, which are the second lowest observed in the 20 year history of this gear. Seventy-five percent of the Yellow Perch observed in both the inshore and offshore nets were from the 2015 and 2016 year classes. The 2013 year class of Perch, which was fairly prominent in the previous year's sampling (43%), made up only 7% of the fish observed in 2017.
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\nTullibee CPE decreased from 2016 by 93% in the inshore nets to 0.7 fish/net and 0.8 lb/net, which is slightly below median level. CPE decreased slightly in the offshore, but was still above the 75th percentile at 32.8 fish/net, while biomass increased to the highest observed at 43.5 lb/net, which suggests few age 1 Tullibee in the population. An aged sub-sample of fish indicated that around 70% of the Tullibee were from the 2013 and 2014 year classes, which ranged in size from 12 to 18 inches; making them less vulnerable to all but the larger piscine predators (Northern Pike and Muskellunge). The difference in magnitude between the inshore and offshore catches over the last several years may reflect a diminished lake-wide population that is no longer over-flowing into the less desirable habitat of the near shore region, or it may represent a behavioral shift into offshore regions due to other environmental factors.
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\nBurbot continued to exhibit a declining trend in number, and are now only occasionally observed in the assessment nets. Rock Bass decreased to 0.8/net, which is median for this species. Smallmouth Bass decreased for the second consecutive year to 1.3/net, which is still above the 75% quartile. Smallmouth Bass also decreased slightly in the offshore nets and are at the second highest observed at 0.55/net.
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\nThe most important prey items for Walleye are sampled in early September using very small mesh gill nets. The primary purpose of this assessment is to monitor the abundance of prey species in the lake to gain insight into their population dynamics, and how that affects the Walleye population. In addition to prey species, this survey also samples young-of-year Walleye.
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\nThe major prey species of piscivorous predators in Mille Lacs is typically small Yellow Perch. Annual fall sampling indicated that moderate-high numbers and biomass of young-of-the-year (YOY) Yellow Perch were available in 2017 when compared across the eight year history of this sampling gear. Yellow Perch of age classes older than YOY were among the lowest observed. Age 0 Tullibee were observed at moderate numbers and biomass, while age 1 Tullibee were at the lowest observed. Spottail Shiners had been generally increasing since 2012, but dropped to the lowest observed in 2017.
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\nAge 0 Walleye in the forage gill nets decreased to below median levels and there were no age 1 Walleye observed. Overall, the forage nets would suggest adequate forage availability, in the form of YOY Yellow Perch and Tullibee, for all sizes of Walleye. The condition factor of Walleye in the fall gill net sampling and cursory inspection of stomach contents suggests that all sizes of Walleye are feeding on the available forage items, but larger fish, particularly mature females, still had a ways to go in order to bulk up to more typical Mille Lacs robustness.
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\nYoung-of-year Walleye are sampled using electrofishing gear in early September. In addition to the forage gill nets, this survey gives us insight into the size and abundance of young-of-year Walleye at the end of their first summer.
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\nAge 0 Walleye CPE in the six electrofishing transects was highly variable in 2017, with the lowest catch rate coming from the Father Hennepin State Park area (58.3 fish/hr) and the highest catch rate coming from the Wealthwood location the following week (502.0 fish/hr). Overall CPE for YOY Walleye was 247.7/hour, which is close to twice the median and suggests that spring reproduction and survival through the summer were very good. The catch rate for age 1 Walleye was below the median at 8.9 Walleye/hr, which suggests that few of the abundant 2016 year class observed the previous year had survived to their second fall. Average length for age 0 Walleye was 5.9 inches, which spanned an extremely wide range of 3.3 inches to 7.6 inches. The average length of age 1 Walleye was relatively high at 9.7 inches. Forage electrofishing runs of two minutes duration showed comparatively high numbers of age 0 Yellow Perch and the lowest observed number of age 1 Yellow Perch. Catches of other species were relatively unremarkable in the six year history of forage sampling, although, in contrast to the forage gill netting, we did observe above median catches of Spottail Shiners.
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\nInvasive Species
\nTransect counts of adult Zebra Mussels were conducted in the latter half of August. Zebra Mussels appear to have peaked in 2012 and have been consistently declining since, with the counts in 2017 continuing to follow the same pattern. Newly introduced invasive species typically exhibit a quick intensive population growth phase that expands beyond carrying capacity when first introduced into a new system and then a decline in numbers as the population begins to adjust toward equilibrium level. The average adult zebra mussel density was 568 mussels/square foot. Zebra Mussel veligers, which are collected in our zooplankton tows, were at relatively low densities across summer, with peak veliger density occurring in early July.
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\nSpiny Water Flea (Bythotrephes) were observed at relatively high levels during each sampling period from May through September. Peak density typically occurs around mid-June. Two peaks occurred in 2017, one at the normal mid-June period at 14.8 Bythotrephes per sample, which is the third highest observed since Spiny Water Flea was first observed in the fall of 2009, and a second peak in mid-August, which was the highest observed at 21.3 Bythotrephes per sample. Both peaks in Bythotrephes density occurred with concurrent spikes in zooplankton density, suggesting that Bythotrphes density in Mille Lacs may be controlled by the availability of zooplankton. Cursory spot checks of fish stomachs show that age 1+ Tullibee and age 1+ Yellow Perch are consuming Spiny Water Flea.
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\nIt appears that Spiny Water Flea have taken a toll on zooplankton numbers and biomass. Native zooplankton are a vital dietary staple for many larval and juvenile fish in Mille Lacs. We have been observing severe declines in various species that belong to three broad functional groups. Currently, all three groups show a severe level of depletion, but small cladocerans and large cladocerans show the greatest decrease over time, where throughout the summer they are now often barely detectable in the samples. An unusual observation for 2017 was that a relatively large bloom of cladocerans and copepods were observed in mid-June and a second relatively large bloom of copepods were observed in mid-August. These spikes in zooplankton density are relatively modest when compared to densities that were observed in the late 2000's, but the last time we observed comparable numbers of zooplankton was in 2013. This may suggest that some minimal threshold of zooplankton density needs to be present in order to obtain adequate numbers of forage fish in the lake.
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\nOverview
\nCurrent indexing data suggests that Walleye numbers and biomass are showing consistent annual improvement since we observed the lowest sampling gear catches ever recorded on Mille Lacs in 2012. This increase in Walleye numbers is largely being fueled by the unusually strong 2013 year class, which has now mostly matured and will be contributing in full to the walleye spawning effort in spring 2018. The 2013 year class is the only current mature cohort of Walleye in Mille Lacs that is being observed above median levels and this lack of age diversity has the potential to become an issue if we were to observe significant declines in this specific year class while no other moderate to high year classes are available. Currently, it would appear that the 2015 cohort is slightly below the median year class strength, but has the potential to recruit as a moderate year class into the spawning stock over the next several years, with the majority of males already mature. Current forage levels appear to be adequate to maintain this year class of fish and are providing a food resource for even smaller Walleyes.
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\nSome of the changes to Walleye numbers and in the Walleye length frequency distribution observed over the last several years appear to be due to various regulations that have been implemented over the past several decades; however, it also appears that major changes are occurring to various fish populations throughout the lake, including Walleye, due to a changing ecosystem. Burbot, a cold water species, have shown severe declines in population which are likely related to a warming climate. Tullibee are also considered a cold water species and while they don't show a decline in population that is as severe as Burbot, their population numbers are showing high variability across years. Further, Tullibee are now rarely found in appreciable numbers in the nearshore fall gill nets, which may be an indication that a smaller population is no longer overflowing from the most prime habitat in the offshore regions of the lake. Conversely, Smallmouth Bass have been increasing over time, which appears to be a regional phenomenon and is consistent with a warming climate. Further, we are observing increasing variability in summer water clarity measurements, with overall clearer water over the last couple decades when compared to data collected prior to the 1980's. Clearer water suggests reduced overall productivity in the system, but it may also convey some competitive advantages to sight oriented predators such as Smallmouth Bass and Northern Pike, while creating a disadvantage for Walleye which tend to find more turbid, low-light conditions advantageous.
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\nDespite a couple of seasonal spikes in zooplankton numbers and biomass in 2017, overall zooplankton metrics remain comparatively low in Mille Lacs for the fifth consecutive year, which is additional evidence of large scale changes occurring with the lake's productivity. Chloropyll-A measurements have been consistently trending downwards since 2008 and mean total phosphorus measurements in 2017 were the lowest observed. All pertinent evidence continues to suggest a system that is much less productive than what was observed just a couple of decades past and a system that is now much less hospitable for Walleye, Tullibee, and Burbot.
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