A targeted survey of the nearshore fish community in Bertha Lake was conducted on June 25-26, 2018 by Fisheries Lake IBI program staff. Sampling stations were evenly spaced around the lake and each was sampled by backpack electrofishing and seining with a 50-foot or 15-foot seine, where possible. Backpack electrofishing was completed at all 10 stations with one site sampled from the boat. A 50-foot seine was used to sample nine stations and one sampling station had conditions that prevented the use of seine. Nearshore sampling captured 22 native species of fish including 9 species that are intolerant of habitat disturbance (Banded Killifish, Blackchin Shiner, Blacknose Shiner, Iowa Darter, Logperch, Longnose Dace, Mimic Shiner, Rock Bass, and Smallmouth Bass) as well as two tolerant species (Fathead Minnow and Green Sunfish).
\n
\nData from this targeted nearshore survey is combined with data from standard gill and trap netting surveys to calculate a Fish-based Index of Biological Integrity (FIBI) that describes the overall health of the lake. The FIBI uses fish community data to measure a lake's health, and the types of fish species present can help identify any stressors that may be negatively affecting the lake environment. The FIBI score, composed of several fish community diversity and composition metrics, indicates the overall health of a lake by comparing it to what is expected for a healthy lake. The FIBI score for Bertha Lake based on this survey is exceptionally high, well above the impairment threshold for aquatic life use determined for similar lakes. Data from this survey will contribute biological information about the health of the fish community to the Pine River Watershed assessment process in coordination with MN Pollution Control Agency.
\n
Bertha Lake is a 334 acre basin in the 14,000 acre Whitefish chain of lakes. Maximum depth is 64 feet and about 42% of its surface area is less than 15 feet deep. Development is heavy, with 113 homes/cabins present on the 3.8 miles of shoreline.In 1995, northern pike, tullibees, bluegills, rock bass and yellow bullheads were found in \"high\" numbers. Lake whitefish, walleyes, white suckers, yellow perch, bowfin (dogfish), brown bullheads, largemouth bass and pumpkinseeds were found in \"average\" numbers. Black bullheads, black crappies and green sunfish were found in \"low\" numbers compared to similar type lakes.
","lengths":{"BLC":{"maximum_length":11,"fishCount":[[10,2],[11,1]],"minimum_length":10},"WTS":{"maximum_length":21,"fishCount":[[17,1],[18,4],[20,3],[21,1],[5,3],[6,9],[7,6],[8,1]],"minimum_length":5},"TLC":{"maximum_length":15,"fishCount":[[10,9],[11,1],[12,6],[13,4],[14,3],[15,1],[7,1],[8,23],[9,24]],"minimum_length":7},"WAE":{"fishCount":[[14,1],[15,1],[16,3],[18,1],[20,1],[22,1],[27,1],[30,1]],"maximum_length":30,"minimum_length":14},"SHR":{"maximum_length":18,"fishCount":[[18,1]],"minimum_length":18},"LKW":{"minimum_length":14,"fishCount":[[14,1],[15,1],[16,1],[17,2],[21,1]],"maximum_length":21},"GRR":{"minimum_length":9,"fishCount":[[18,1],[19,1],[21,1],[22,4],[23,1],[9,1]],"maximum_length":23},"PMK":{"fishCount":[[3,1],[4,5],[5,10],[6,6]],"maximum_length":6,"minimum_length":3},"HSF":{"minimum_length":3,"maximum_length":9,"fishCount":[[3,1],[5,4],[6,4],[7,1],[9,1]]},"YEB":{"minimum_length":5,"maximum_length":12,"fishCount":[[10,24],[11,7],[12,4],[5,1],[7,1],[8,12],[9,17]]},"BLB":{"maximum_length":11,"fishCount":[[11,1],[9,1]],"minimum_length":9},"YEP":{"minimum_length":3,"fishCount":[[10,1],[3,27],[4,5],[5,32],[6,49],[7,7],[8,4]],"maximum_length":10},"BOF":{"minimum_length":26,"fishCount":[[26,1],[27,2],[28,1]],"maximum_length":28},"GSF":{"maximum_length":5,"fishCount":[[4,1],[5,1]],"minimum_length":4},"NOP":{"maximum_length":32,"fishCount":[[14,1],[16,2],[17,6],[18,9],[19,10],[20,9],[21,18],[22,5],[23,8],[24,4],[25,3],[26,3],[27,4],[28,2],[29,1],[30,1],[31,2],[32,1]],"minimum_length":14},"LMB":{"minimum_length":2,"fishCount":[[2,18],[6,7],[7,3]],"maximum_length":7},"RKB":{"minimum_length":1,"fishCount":[[10,7],[11,1],[4,1],[5,6],[6,13],[7,9],[8,14],[9,8],[1,1],[2,1]],"maximum_length":11},"BLG":{"minimum_length":1,"maximum_length":9,"fishCount":[[1,2],[3,45],[4,211],[5,198],[6,173],[7,80],[8,15],[9,5]]},"BRB":{"minimum_length":9,"fishCount":[[11,4],[12,1],[9,1]],"maximum_length":12}},"headerInfo":{"wb_id":"18035500","wb_alt_name":"","survey_id":"114305","survey_type":"Re-Survey","wb_type":"Lake","wb_name":"Bertha","id_date":"1995-06-14","county":"Crow Wing"},"surveyID":"114305","surveyDate":"1995-06-14","surveyType":"Standard Survey"},{"surveyType":"Targeted Survey","surveyID":"17972219847497000","headerInfo":{"county":"Crow Wing","id_date":"2022-07-25","wb_name":"Bertha","wb_type":"Lake","survey_type":"Targeted Survey","survey_id":"17972219847497000","wb_alt_name":"","wb_id":"18035500"},"surveyDate":"2022-07-25","lengths":{},"narrative":"A targeted survey of nearshore fish species in Bertha Lake was conducted on July 25, 2022, by DNR Index of Biological Integrity (IBI) Program staff. Sampling sites were evenly spaced around the lake, and each was sampled by backpack electrofishing and seining with a 50-foot or 15-foot seine, where possible. Backpack electrofishing was completed at nine sampling stations, but one station was sampled from the boat due to site conditions. Similarly, a 50-foot seine was used to sample nine stations, and site conditions prevented the use of seines at one station. Nearshore sampling captured 20 species of fish including eight species that are intolerant of disturbance (i.e., Banded Killifish, Blackchin Shiner, Blacknose, Logperch, Longnose Dace, Mimic Shiner, Rock Bass, and Smallmouth Bass) and two that are tolerant of disturbance (i.e., Fathead Minnow and Green Sunfish).
\n
\nThe nearshore data will be combined with trap net and gill net data from survey planned in 2024 to describe the fish community and provide a Fish-based IBI (FIBI) score. The FIBI uses fish community data to measure a lake's health, and the types of fish species present can help identify any stressors that may be negatively affecting the lake environment. In Minnesota lakes, certain fish species cannot survive without clean water and a healthy habitat (e.g., Blackchin Shiner, Logperch, and Longnose Dace), while other species are tolerant of degraded conditions (e.g., Fathead Minnow and Green Sunfish). The FIBI score, composed of several fish community diversity and composition metrics, indicates the overall health of a lake by comparing it to what is expected for a healthy lake. For additional information on the FIBI, search for \"lake index of biological integrity\" on the mndnr.gov website.
\n
\nResults from this survey indicate that the fish community in Bertha Lake is healthy. Data from these surveys will contribute biological information about the health of the fish community to the Pine River Watershed assessment process in coordination with MN Pollution Control Agency.
\n
\nA temperature-dissolved oxygen profile was collected in the deepest basin on Bertha Lake on July 26th, 2022, to evaluate the amount of cold, oxygenated water (i.e., oxythermal habitat) available to Lake Whitefish and Cisco, also known as Tullibee. Based on the profile, the top of the thermocline (i.e., the location in the water column with the sharpest transition from warm to cold water) occurred at approximately 20 feet. Dissolved oxygen decreased to below 3.0 mg/L at 31.0 feet, which was below the thermocline, at the time of sampling. The temperature at which dissolved oxygen decreased to below 3.0 mg/L (i.e., TDO3, a single variable to characterize oxythermal habitat) was 9.5°C (49.1°F).
\n
\nTDO3 values cooler than 17.2°C for Lake Whitefish or 21.5°C for Cisco indicate that oxythermal conditions are favorable for both species. Dissolved oxygen concentrations below the thermocline indicate that suitable oxythermal habitat for Lake Whitefish and Cisco was available across a range of depths at the time of sampling during the summer of 2022. Data collected in 1993-2002 further indicate suitable oxythermal habitat across years, with the least favorable conditions recorded in 2002. When adequate oxythermal habitat is available, Lake Whitefish or Cisco are not squeezed into unfavorable, warmer water conditions and therefore do not experience higher levels of stress.
\n
Net catches for bowfin, lake whitefish, northern pike, yellow bullhead, brown bullhead, rock bass, pumpkinseed and blue gill were all above the third quartile for each species. This would indicate high populations for these species. The yellow perch and walleye catch rates were low, below the first quartiles, suggesting low population present.
","surveySubType":"Re-Survey","fishCatchSummaries":[{"averageWeight":"0.63","totalCatch":6,"totalWeight":3.8,"CPUE":"0.75","quartileWeight":"0.3-0.9","quartileCount":"0.3-1.7","species":"BLB","gear":"Standard trap nets","gearCount":8},{"species":"BRB","quartileCount":"0.3-1.0","gearCount":8,"gear":"Standard trap nets","totalCatch":17,"averageWeight":"0.68","quartileWeight":"0.7-1.0","CPUE":"2.12","totalWeight":11.5},{"species":"YEP","quartileCount":"0.4-2.3","gear":"Standard trap nets","gearCount":8,"averageWeight":"0.37","totalCatch":3,"quartileWeight":"0.1-0.2","totalWeight":1.1,"CPUE":"0.38"},{"averageWeight":"0.36","totalCatch":58,"quartileWeight":"0.4-0.7","CPUE":"9.67","totalWeight":20.8,"species":"YEB","quartileCount":"1.0-6.0","gear":"Standard gill nets","gearCount":6},{"totalCatch":97,"averageWeight":"2.52","CPUE":"16.17","totalWeight":244.7,"quartileWeight":"1.5-3.2","quartileCount":"2.2-8.7","species":"NOP","gearCount":6,"gear":"Standard gill 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nets","quartileCount":"0.3-1.9","species":"BLB","totalWeight":0.1,"CPUE":"0.17","quartileWeight":"0.3-0.9","totalCatch":1,"averageWeight":"0.10"},{"totalWeight":0.1,"CPUE":"0.17","quartileWeight":"0.1-0.2","averageWeight":"0.10","totalCatch":1,"gear":"Standard gill nets","gearCount":6,"quartileCount":"1.5-13.8","species":"YEP"},{"quartileWeight":"0.5-1.1","CPUE":"0.33","totalWeight":1.2,"averageWeight":"0.60","totalCatch":2,"gear":"Standard gill nets","gearCount":6,"species":"BRB","quartileCount":"0.3-1.8"},{"gearCount":8,"gear":"Standard trap nets","quartileCount":"0.2-0.7","species":"WAE","CPUE":"0.12","totalWeight":1.7,"quartileWeight":"0.7-2.8","totalCatch":1,"averageWeight":"1.70"},{"totalCatch":7,"averageWeight":"0.34","CPUE":"0.88","totalWeight":2.4,"quartileWeight":"0.2-0.7","quartileCount":"0.4-1.5","species":"LMB","gearCount":8,"gear":"Standard trap nets"},{"averageWeight":"0.21","totalCatch":1052,"CPUE":"131.50","totalWeight":220.8,"quartileWeight":"0.1-0.2","quartileCount":"7.7-43.4","species":"BLG","gear":"Standard trap nets","gearCount":8},{"totalCatch":83,"averageWeight":"0.17","CPUE":"10.38","totalWeight":14.3,"quartileWeight":"0.1-0.2","quartileCount":"1.4-5.9","species":"PMK","gearCount":8,"gear":"Standard trap nets"},{"averageWeight":"5.07","totalCatch":11,"quartileWeight":"2.6-4.9","CPUE":"1.38","totalWeight":55.8,"species":"BOF","quartileCount":"0.3-1.0","gear":"Standard trap nets","gearCount":8},{"averageWeight":"2.41","totalCatch":12,"CPUE":"1.50","totalWeight":28.9,"quartileWeight":"1.0-2.8","quartileCount":"0.2-0.7","species":"WTS","gear":"Standard trap nets","gearCount":8},{"gear":"Standard trap nets","gearCount":8,"quartileCount":"0.5-2.2","species":"BLC","totalWeight":5,"CPUE":"1.88","quartileWeight":"0.3-0.5","averageWeight":"0.33","totalCatch":15}]},{"narrative":"Bertha Lake is a 344 acre basin in the 14,000 acre Whitefish chain of lakes in northern Crow Wing County. Maximum depth is 64 feet and about 42% of the surface area is less than 15 feet deep. Water clarity is good at 10.5 feet. Development is heavy with 113 homes/cabins present along the 3.8 miles of shoreline.In the 2000 population assessment northern pike, bluegill, pumpkinseed, rock bass and yellow bullheads were found in high numbers. Northern pike sampled ranged from 7.5 inches to 35 inches and had a mean weight of 2.6 pounds. Sampled walleye ranged from 11.3 to 31 inches in length. Mean weight was 2.48 pounds. Lake whitefish, walleye, tullibee, white suckers, yellow perch and largemouth bass were found in average numbers. Black bullheads were found in low numbers compared to other class 23 lakes. All species exhibited good growth rates.
","lengths":{"GRR":{"maximum_length":25,"fishCount":[[18,1],[19,2],[22,1],[23,1],[24,2],[25,2]],"minimum_length":18},"PMK":{"fishCount":[[10,2],[3,6],[4,39],[5,77],[6,31],[7,5],[8,4]],"maximum_length":10,"minimum_length":3},"HSF":{"maximum_length":7,"fishCount":[[4,4],[5,4],[6,9],[7,7]],"minimum_length":4},"YEB":{"minimum_length":7,"fishCount":[[10,37],[11,17],[12,7],[13,1],[7,1],[8,22],[9,26]],"maximum_length":13},"BLB":{"minimum_length":8,"maximum_length":8,"fishCount":[[8,1]]},"YEP":{"fishCount":[[10,1],[4,1],[5,9],[6,14],[7,6],[9,1]],"maximum_length":10,"minimum_length":4},"BOF":{"minimum_length":21,"fishCount":[[21,1],[23,1],[24,1],[25,3]],"maximum_length":25},"NOP":{"maximum_length":38,"fishCount":[[14,1],[15,1],[16,1],[17,5],[18,12],[19,18],[20,20],[21,12],[22,10],[23,7],[24,7],[25,4],[26,2],[28,1],[29,1],[30,2],[35,1],[38,1],[7,1]],"minimum_length":7},"RKB":{"maximum_length":10,"fishCount":[[10,2],[3,1],[4,1],[5,9],[6,16],[7,24],[8,3],[9,7]],"minimum_length":3},"LMB":{"minimum_length":1,"fishCount":[[0,2],[1,2],[10,10],[11,7],[12,7],[13,4],[14,3],[15,2],[5,1],[6,3],[7,6],[8,2],[9,7]],"maximum_length":15},"BLG":{"minimum_length":2,"maximum_length":8,"fishCount":[[2,1],[3,97],[4,216],[5,188],[6,271],[7,164],[8,40]]},"BRB":{"fishCount":[[11,1],[13,1],[14,1],[9,1]],"maximum_length":14,"minimum_length":9},"WTS":{"maximum_length":20,"fishCount":[[14,1],[16,2],[17,1],[18,6],[19,2],[20,1]],"minimum_length":14},"BLC":{"minimum_length":4,"maximum_length":11,"fishCount":[[11,1],[4,1],[6,1],[7,3],[8,2]]},"TLC":{"minimum_length":6,"fishCount":[[10,2],[11,2],[12,1],[14,1],[6,2],[7,2],[8,2],[9,2]],"maximum_length":14},"WAE":{"fishCount":[[11,2],[12,5],[14,1],[15,2],[16,4],[17,3],[19,2],[20,1],[21,1],[23,1],[25,1],[27,1],[30,1],[31,1]],"maximum_length":31,"minimum_length":11},"SLR":{"minimum_length":22,"fishCount":[[22,2],[24,1]],"maximum_length":24},"LKW":{"maximum_length":21,"fishCount":[[13,1],[14,1],[15,1],[17,1],[18,1],[19,1],[20,1],[21,2]],"minimum_length":13}},"surveySubType":"Population 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Wing","survey_id":"114455","wb_type":"Lake","survey_type":"Population Assessment","wb_id":"18035500","wb_alt_name":""},"surveyID":"114455","surveyDate":"2000-06-07"},{"lengths":{"HSF":{"minimum_length":4,"fishCount":[[4,2],[5,5],[6,9],[7,9],[8,1]],"maximum_length":8},"GRR":{"minimum_length":22,"maximum_length":24,"fishCount":[[22,1],[24,1]]},"PMK":{"minimum_length":3,"maximum_length":6,"fishCount":[[3,1],[4,5],[5,29],[6,13]]},"BLB":{"fishCount":[[10,1]],"maximum_length":10,"minimum_length":10},"YEB":{"fishCount":[[10,16],[11,4],[8,2],[9,8]],"maximum_length":11,"minimum_length":8},"BOF":{"minimum_length":21,"fishCount":[[21,1],[22,1],[23,2],[24,2],[26,1],[28,2]],"maximum_length":28},"YEP":{"maximum_length":7,"fishCount":[[5,14],[6,1],[7,1]],"minimum_length":5},"NOP":{"maximum_length":37,"fishCount":[[13,1],[15,4],[16,7],[17,7],[18,9],[19,7],[20,15],[21,9],[22,7],[23,11],[24,11],[25,7],[26,3],[27,3],[29,2],[30,1],[33,1],[34,1],[37,1]],"minimum_length":13},"RKB":{"maximum_length":9,"fishCount":[[3,5],[4,2],[5,6],[6,7],[7,14],[8,5],[9,2]],"minimum_length":3},"LMB":{"maximum_length":13,"fishCount":[[10,3],[13,1],[5,2],[7,2],[8,1],[9,1]],"minimum_length":5},"BLG":{"maximum_length":8,"fishCount":[[3,15],[4,29],[5,82],[6,93],[7,57],[8,1]],"minimum_length":3},"BRB":{"maximum_length":12,"fishCount":[[10,1],[11,4],[12,1]],"minimum_length":10},"BLC":{"maximum_length":9,"fishCount":[[7,1],[8,4],[9,3]],"minimum_length":7},"WTS":{"minimum_length":8,"maximum_length":25,"fishCount":[[16,1],[17,2],[18,2],[19,3],[25,1],[8,1]]},"TLC":{"maximum_length":17,"fishCount":[[10,72],[11,51],[12,4],[13,1],[14,2],[15,1],[16,1],[17,2],[4,1],[6,6],[7,40],[8,59],[9,41]],"minimum_length":4},"WAE":{"fishCount":[[15,1],[16,3],[18,2],[19,1],[21,3],[22,2],[26,1],[28,3]],"maximum_length":28,"minimum_length":15},"SHR":{"maximum_length":15,"fishCount":[[15,1]],"minimum_length":15},"LKW":{"minimum_length":10,"maximum_length":22,"fishCount":[[10,2],[11,2],[14,1],[17,1],[21,1],[22,1]]}},"narrative":"Bertha is part of the Whitefish chain of lakes located in northern Crow Wing County. Access to it can be gained via channel from Whitefish or Clamshell lakes. Development is heavy on the lake, with 113 homes/cabins being counted during the 1995 survey along 2.4 miles of shoreline.Walleyes are not stocked directly into Bertha, but fry and fingerlings are stocked into connected Whitefish Lake. The walleye catch rate (1.3/gill net) was average in 2004 when compared to similar lakes. Average size was 22.0\" and 4.3 lbs. All of the fish were over 12\".The northern pike catch rate was high (11.1/gill net). Size averaged 21.8\" and 2.4 lbs., with 27% of the fish being 24\" or larger.Largemouth bass were caught in average numbers in both gill nets (0.6/net) and trap nets (0.6/net). Average length was 10.9\" in gill nets and 6.6\" in trap nets. Only one fish was 12\" or larger.The black crappie catch rate was average in gill nets (0.6/net), with an average length of 8.3\". The trap net catch rate of 0.3/net was low. These fish had an average length of 9.6\". When both net types were combined, 88% of the fish were 8\" or larger.The bluegill catch rate was average compared to similar lakes (28.2/trap net). Average length was 6.1\" and 20% of the fish were 7\" or larger.The lake whitefish catch rate was also in the average category. Size averaged 15.0\" and 1.5 lbs.Other fish species captured included black bullhead, bowfin (dogfish), brown bullhead, greater redhorse, hybrid sunfish, pumpkinseed, rock bass, shorthead redhorse, tullibee (cisco), white sucker, and yellow bullhead.
","fishCatchSummaries":[{"totalWeight":1797,"CPUE":"0.56","quartileWeight":"0.7-1.0","totalCatch":5,"averageWeight":"0.79","gearCount":9,"gear":"Standard trap nets","quartileCount":"0.3-1.0","species":"BRB"},{"gearCount":9,"gear":"Standard gill nets","quartileCount":"1.0-6.0","species":"YEB","CPUE":"2.11","totalWeight":4707,"quartileWeight":"0.4-0.7","totalCatch":19,"averageWeight":"0.55"},{"totalWeight":108451,"CPUE":"11.11","quartileWeight":"1.5-3.2","totalCatch":100,"averageWeight":"2.39","gearCount":9,"gear":"Standard gill nets","quartileCount":"2.2-8.7","species":"NOP"},{"species":"RKB","quartileCount":"0.7-4.4","gearCount":9,"gear":"Standard gill nets","totalCatch":16,"averageWeight":"0.16","quartileWeight":"0.2-0.4","totalWeight":1174,"CPUE":"1.78"},{"totalCatch":11,"averageWeight":"0.61","totalWeight":3041,"CPUE":"1.22","quartileWeight":"0.5-0.9","quartileCount":"1.0-5.3","species":"YEB","gearCount":9,"gear":"Standard trap 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nets","gearCount":9,"quartileCount":"N/A","species":"BLG"},{"gearCount":9,"gear":"Standard gill nets","species":"PMK","quartileCount":"N/A","quartileWeight":"N/A","CPUE":"0.89","totalWeight":444,"totalCatch":8,"averageWeight":"0.12"},{"quartileCount":"0.2-0.3","species":"BOF","gearCount":9,"gear":"Standard gill nets","totalCatch":3,"averageWeight":"4.19","CPUE":"0.33","totalWeight":5700,"quartileWeight":"3.0-5.3"},{"species":"TLC","quartileCount":"1.3-10.4","gearCount":9,"gear":"Standard gill nets","totalCatch":281,"averageWeight":"0.34","quartileWeight":"0.3-1.0","totalWeight":43073,"CPUE":"31.22"},{"quartileCount":"0.5-2.0","species":"WTS","gear":"Standard gill nets","gearCount":9,"averageWeight":"2.73","totalCatch":10,"totalWeight":12371,"CPUE":"1.11","quartileWeight":"1.6-2.6"},{"quartileWeight":"0.2-0.5","totalWeight":738,"CPUE":"0.56","totalCatch":5,"averageWeight":"0.33","gearCount":9,"gear":"Standard gill nets","species":"BLC","quartileCount":"0.3-1.7"},{"quartileWeight":"0.3-0.9","CPUE":"0.11","totalWeight":300,"averageWeight":"0.66","totalCatch":1,"gear":"Standard gill nets","gearCount":9,"species":"BLB","quartileCount":"0.3-1.9"},{"averageWeight":"0.09","totalCatch":16,"quartileWeight":"0.1-0.2","totalWeight":633,"CPUE":"1.78","species":"YEP","quartileCount":"1.5-13.8","gear":"Standard gill nets","gearCount":9},{"species":"BRB","quartileCount":"0.3-1.8","gearCount":9,"gear":"Standard gill nets","totalCatch":1,"averageWeight":"0.66","quartileWeight":"0.5-1.1","CPUE":"0.11","totalWeight":300},{"gear":"Standard trap nets","gearCount":9,"quartileCount":"0.2-0.7","species":"WAE","CPUE":"0.44","totalWeight":4945,"quartileWeight":"0.7-2.8","averageWeight":"2.73","totalCatch":4},{"averageWeight":"0.14","totalCatch":5,"quartileWeight":"0.2-0.7","CPUE":"0.56","totalWeight":318,"species":"LMB","quartileCount":"0.4-1.5","gear":"Standard trap nets","gearCount":9},{"totalCatch":254,"averageWeight":"0.10","totalWeight":12080,"CPUE":"28.22","quartileWeight":"0.1-0.2","quartileCount":"7.7-43.4","species":"BLG","gearCount":9,"gear":"Standard trap nets"},{"gearCount":9,"gear":"Standard trap nets","quartileCount":"1.4-5.9","species":"PMK","CPUE":"4.44","totalWeight":2825,"quartileWeight":"0.1-0.2","totalCatch":40,"averageWeight":"0.16"},{"gearCount":9,"gear":"Standard trap nets","quartileCount":"0.3-1.0","species":"BOF","totalWeight":16000,"CPUE":"0.67","quartileWeight":"2.6-4.9","totalCatch":6,"averageWeight":"5.88"},{"gearCount":9,"gear":"Standard trap nets","quartileCount":"0.5-2.2","species":"BLC","CPUE":"0.33","totalWeight":632,"quartileWeight":"0.3-0.5","totalCatch":3,"averageWeight":"0.46"}],"surveySubType":"Population Assessment","surveyType":"Standard Survey","surveyDate":"2005-06-13","headerInfo":{"wb_alt_name":"","wb_id":"18035500","county":"Crow Wing","wb_name":"Bertha","id_date":"2005-06-13","survey_type":"Population Assessment","wb_type":"Lake","survey_id":"114599"},"surveyID":"114599"},{"surveyDate":"2018-06-11","surveyID":"16511816228569000","headerInfo":{"county":"Crow Wing","id_date":"2018-06-11","wb_name":"Bertha","wb_type":"Lake","survey_type":"Standard Survey","survey_id":"16511816228569000","wb_alt_name":"","wb_id":"18035500"},"surveyType":"Standard Survey","fishCatchSummaries":[{"CPUE":"0.38","totalWeight":1433,"quartileWeight":"0.7-1.0","averageWeight":"1.05","totalCatch":3,"gear":"Standard trap nets","gearCount":8,"quartileCount":"0.3-1.0","species":"BRB"},{"averageWeight":"0.06","totalCatch":1,"CPUE":"0.12","totalWeight":29,"quartileWeight":"0.1-0.2","quartileCount":"0.4-2.3","species":"YEP","gear":"Standard trap nets","gearCount":8},{"averageWeight":"0.79","totalCatch":3,"totalWeight":1074,"CPUE":"0.33","quartileWeight":"0.4-0.7","quartileCount":"1.0-6.0","species":"YEB","gear":"Standard gill nets","gearCount":9},{"gear":"Standard gill nets","gearCount":9,"species":"NOP","quartileCount":"2.2-8.7","quartileWeight":"1.5-3.2","CPUE":"7.89","totalWeight":73729,"averageWeight":"2.29","totalCatch":71},{"totalCatch":14,"averageWeight":"0.46","quartileWeight":"0.2-0.4","CPUE":"1.56","totalWeight":2902,"species":"RKB","quartileCount":"0.7-4.4","gearCount":9,"gear":"Standard gill nets"},{"totalWeight":13495,"CPUE":"5.38","quartileWeight":"0.5-0.9","totalCatch":43,"averageWeight":"0.69","gearCount":8,"gear":"Standard trap nets","quartileCount":"1.0-5.3","species":"YEB"},{"totalCatch":9,"averageWeight":"1.55","CPUE":"1.12","totalWeight":6313,"quartileWeight":"N/A","quartileCount":"N/A","species":"NOP","gearCount":8,"gear":"Standard trap nets"},{"quartileCount":"0.2-1.5","species":"SHR","gear":"Standard gill nets","gearCount":9,"averageWeight":"3.17","totalCatch":1,"totalWeight":1437,"CPUE":"0.11","quartileWeight":"1.4-2.7"},{"totalWeight":11640,"CPUE":"1.00","quartileWeight":"0.5-1.5","averageWeight":"2.85","totalCatch":9,"gear":"Standard gill nets","gearCount":9,"quartileCount":"0.4-5.9","species":"LKW"},{"gear":"Standard trap nets","gearCount":8,"species":"RKB","quartileCount":"0.8-3.7","quartileWeight":"0.2-0.4","totalWeight":10375,"CPUE":"7.00","averageWeight":"0.41","totalCatch":56},{"quartileWeight":"1.2-3.0","totalWeight":38034,"CPUE":"1.67","averageWeight":"5.59","totalCatch":15,"gear":"Standard gill nets","gearCount":9,"species":"WAE","quartileCount":"1.0-5.0"},{"averageWeight":"0.36","totalCatch":18,"totalWeight":2912,"CPUE":"2.25","quartileWeight":"N/A","quartileCount":"N/A","species":"HSF","gear":"Standard trap nets","gearCount":8},{"CPUE":"0.78","totalWeight":4355,"quartileWeight":"0.5-1.2","totalCatch":7,"averageWeight":"1.37","gearCount":9,"gear":"Standard gill nets","quartileCount":"0.5-1.7","species":"LMB"},{"quartileWeight":"N/A","totalWeight":844,"CPUE":"1.00","totalCatch":9,"averageWeight":"0.21","gearCount":9,"gear":"Standard gill nets","species":"BLG","quartileCount":"N/A"},{"quartileCount":"N/A","species":"PMK","gear":"Standard gill nets","gearCount":9,"averageWeight":"0.14","totalCatch":4,"CPUE":"0.44","totalWeight":256,"quartileWeight":"N/A"},{"gear":"Standard gill nets","gearCount":9,"quartileCount":"0.2-0.3","species":"BOF","CPUE":"0.33","totalWeight":5399,"quartileWeight":"3.0-5.3","averageWeight":"3.97","totalCatch":3},{"averageWeight":"0.33","totalCatch":133,"CPUE":"14.78","totalWeight":19704,"quartileWeight":"0.3-1.0","quartileCount":"1.3-10.4","species":"TLC","gear":"Standard gill nets","gearCount":9},{"quartileCount":"0.5-2.0","species":"WTS","gearCount":9,"gear":"Standard gill nets","totalCatch":10,"averageWeight":"3.10","totalWeight":14041,"CPUE":"1.11","quartileWeight":"1.6-2.6"},{"gear":"Standard gill nets","gearCount":9,"quartileCount":"0.3-1.7","species":"BLC","totalWeight":121,"CPUE":"0.44","quartileWeight":"0.2-0.5","averageWeight":"0.07","totalCatch":4},{"quartileCount":"1.5-13.8","species":"YEP","gear":"Standard gill nets","gearCount":9,"averageWeight":"0.09","totalCatch":1,"CPUE":"0.11","totalWeight":39,"quartileWeight":"0.1-0.2"},{"quartileWeight":"0.7-2.8","totalWeight":2405,"CPUE":"0.25","averageWeight":"2.65","totalCatch":2,"gear":"Standard trap nets","gearCount":8,"species":"WAE","quartileCount":"0.2-0.7"},{"species":"BUB","quartileCount":"0.2-0.3","gearCount":9,"gear":"Standard gill nets","totalCatch":2,"averageWeight":"1.29","quartileWeight":"1.5-3.0","totalWeight":1170,"CPUE":"0.22"},{"gearCount":8,"gear":"Standard trap nets","quartileCount":"0.4-1.5","species":"LMB","CPUE":"1.12","totalWeight":3166,"quartileWeight":"0.2-0.7","totalCatch":9,"averageWeight":"0.78"},{"species":"BLG","quartileCount":"7.7-43.4","gear":"Standard trap nets","gearCount":8,"averageWeight":"0.16","totalCatch":245,"quartileWeight":"0.1-0.2","totalWeight":18098,"CPUE":"30.62"},{"totalWeight":3745,"CPUE":"6.00","quartileWeight":"0.1-0.2","averageWeight":"0.17","totalCatch":48,"gear":"Standard trap nets","gearCount":8,"quartileCount":"1.4-5.9","species":"PMK"},{"gearCount":8,"gear":"Standard trap nets","species":"BOF","quartileCount":"0.3-1.0","quartileWeight":"2.6-4.9","CPUE":"1.88","totalWeight":35102,"totalCatch":15,"averageWeight":"5.16"},{"gearCount":8,"gear":"Standard trap nets","species":"BLC","quartileCount":"0.5-2.2","quartileWeight":"0.3-0.5","totalWeight":975,"CPUE":"0.75","totalCatch":6,"averageWeight":"0.36"}],"surveySubType":"Standard Survey","narrative":"Bertha Lake is a 334 acre lake, and is part of the Whitefish Chain located in northern Crow Wing County. The maximum depth is 64 feet, with 43% of the lake 15' or less. Water clarity is good with a secchi depth of 19.0 ft.
\n
\nNorthern pike were sampled in average numbers, when compared to similar lakes, at 7.9/gill net. Average length was 21.2\", with 24% measuring at least 24\" in length. Fish up to 35.9\" were sampled. Lakes in this part of the state have a new northern pike regulation enacted in 2018: possession limit of 10 with not more than 2 over 26\". All from 22\"-26\" must be immediately released. Please refer to the current Minnesota Fishing Regulations for additional information.
\n
\nWalleyes are not stocked into Bertha, but are stocked annually as fry and every other year as fingerlings into the Whitefish Chain. Walleyes can move through the chain and into Bertha. Walleye numbers were average at 1.7/gill net. The walleyes sampled were nice size, with an average length of 24.2\". Walleyes ranged from 15.0\" to 29.8\".
\n
\nLargemouth bass were sampled in average numbers in gill nets at 0.8/net. Average length was 13.5\". Largemouth bass electrofishing was conducted at various stations across the Whitefish Chain of Lakes, resulting in a combined catch rate of 68.8/hr run-time. Average length was 13.5\". Five smallmouth bass were also netted while electrofishing. All but one were over 17\".
\n
\nBlack crappies were sampled in low numbers in gill nets at 0.4/net. Average length was 5.1\". The trap net catch was average at 0.8/net, with an average length of 8.5\". For both gears combined 40% measured at least 8\" in length. Bluegills were also sampled in average numbers at 30.6/trap net. Average length was 5.9\", with 36% at least 7\" in length.
\n
\nBertha Lake is designated as AIS (aquatic invasive species) infested waters because of zebra mussels. Lake users are required to inspect and remove any aquatic plants and animals from their watercraft and trailers as well as pull the plug and drain all water from the watercraft, including bilges, livewells and baitwells.
\n
Bertha Lake is a 334 acre lake and is part of the Whitefish Chain located in northern Crow Wing County. The maximum depth is 64 feet, with 43% of the lake 15' or less.
\n
\nOne thing unique to Bertha, compared to other lakes in the Brainerd Area, is that while the numbers of Walleye and Northern Pike may not be high, large fish are common. The presence of Tullibee (Cisco) likely contributes to the quality size of large predators. Numbers of Tullibee (Cisco) were a little lower this survey (6.2/net) than the previous survey (14.8/net), however, the catch has been as high as 31.2/net. Walleyes are not stocked into Bertha but are stocked annually as fry and every other year as fingerlings into the Whitefish Chain; Walleyes can move throughout the chain and into Bertha. Walleye numbers were average at 1.4/net, but as mentioned previously, they were nice size. They had an average length of 24.4\", with fish up to 28.4\" present. It was a similar story with Northern Pike, with 29% of sampled pike 26\" or larger. Catch rates from 2024 (8.6/net) were comparable to the previous survey (7.9/net).
\n
\nLargemouth Bass electrofishing was conducted at various stations across the Whitefish Chain of Lakes, resulting in a combined catch rate of 44.9/hour. Average length was 13.1\" and 65% were over 12\", with fish up to 19.2\" sampled. Three Smallmouth Bass were also netted while electrofishing and all of them were over 16\".
\n
\nBlack Crappies were sampled in low numbers in both gill nets (0.3/net) and trap nets (0.2/net). Fish were around the size that anglers begin to harvest them, with 80% of the fish measuring 8\" or larger, but the largest fish was only 9.4\". Bluegills were sampled in average numbers at 26.0/trap net. With an average length of 5.2\" and only 8% of the fish measuring 7\" or larger, anglers may want to look elsewhere in the chain to target panfish. A special regulation on the Whitefish Chain reduces the daily limit of Sunfish and Crappie to 5 of each.
\n
\nBertha Lake is designated as AIS (aquatic invasive species) infested waters because of zebra mussels. Lake users are required to inspect and remove any aquatic plants and animals from their watercraft and trailers as well as pull the plug and drain all water from the watercraft, including bilges, livewells and baitwells.
A temperature-dissolved oxygen profile was collected in the deepest basin on Bertha Lake on August 8th, 2023 to evaluate the amount of cold, oxygenated water (i.e., oxythermal habitat) available to Lake Whitefish and Cisco, also known as Tullibee. Based on the profile, the top of the thermocline (i.e., the location in the water column with the sharpest transition from warm to cold water) occurred at approximately 17 feet. Dissolved oxygen decreased to below 3.0 mg/L at 37.1 feet, which was below the thermocline, at the time of sampling. The temperature at which dissolved oxygen decreased to below 3.0 mg/L (i.e., TDO3, a single variable to characterize oxythermal habitat) was 6.7°C (44.1°F).
\n
\nTDO3 values cooler than 17.2°C for Lake Whitefish or 21.5°C for Cisco indicate that oxythermal conditions are favorable for these species. Dissolved oxygen concentrations below the thermocline indicate that suitable oxythermal habitat for these species was available across a range of depths at the time of sampling. Data collected in 1993, 1994, 1995, 1996, 1997, 1998, 2002, and 2022 also indicated suitable oxythermal habitat. When adequate oxythermal habitat is available, Lake Whitefish or Cisco are not squeezed into unfavorable, warmer water conditions and therefore do not experience higher levels of stress.
Bertha Lake is 334 acres in size and is part of the Whitefish chain of lakes in northern Crow Wing County. While there is no public access on Bertha, access may be gained via channel from Clamshell Lake or Whitefish Lake. Bertha Lake has a maximum depth of 64 feet with 43% of the lake 15 feet or less. The lakeshore is heavily developed with 147 homes/cabins along nearly 3.9 miles of shoreline.
\n
\nEven though walleyes aren't stocked directly in Bertha, a walleye fishery exists due to the connection with Whitefish Lake which is stocked with fry and fingerlings. The walleye catch rate of 2.9/gill net is average when compared to similar lakes. The size of walleyes was impressive, with a 22.3\" and 4.2 lb average. Fish up to 29.9\" were caught with nearly 97% of the fish 14\" or larger.
\n
\nNorthern pike numbers are well above average compared to similar lakes with a catch rate of 14.4/gill net. The average length of these fish was 20.3\" with a weight of 2.0 lbs. There were fish up to 35.2\" sampled with the potential for larger fish to exist due to an abundance of tullibee (cisco), which are an important forage fish. Tullibee (cisco) catch rates were also above average at 23.8/gill net.
\n
\nLargemouth bass were caught at a rate of 0.7/gill net. The average size of these fish was 12.6\" and 1.1 lbs. Only one smallmouth bass was caught which was 16.7\" and 2.6 lbs. Although standard survey nets don't sample largemouth bass effectively, electrofishing was conducted on other lakes on the Whitefish chain where the catch rate was 112.5/hr. The average size was similar to Bertha with fish up to 18.7\" sampled during electrofishing. Given the connection of the lakes it can be assumed that there is fish movement among basins.
\n
\nBluegill were sampled at a rate of 29.9/trap net in 2011. Their average length was 6.8\". Overall, 52% of bluegill were 7\" or larger. Black crappie abundance was relatively low, with a catch rate of 0.6/trap net and only 0.3/gill net. The black crappies in the gill nets had a decent average size of 11.1\". The average size for black crappies in trap nets was slightly smaller at 8.8\".
\n
\nLake whitefish represent another species that anglers may target. They were sampled at a rate of 0.9/gill net. Their size was decent, with an average length of 20.1\" and 3.0 lbs. Fish up to 23.8\" were caught during the survey.
\n
\nSome other fish species sampled during the survey included bowfin (dogfish), brown bullhead, greater redhorse, hybrid sunfish, pumpkinseed, rock bass, shorthead redhorse, silver redhorse, white sucker, yellow bullhead, and yellow perch. While conducting seining and backpack electrofishing, various other species were sampled including johnny darter, banded killifish, blackchin shiner, bluntnose minnow, and green sunfish.
\n
Temperature and dissolved oxygen profiles were collected in the deepest basin in Bertha Lake on August 14, 2024, to evaluate the quantity and quality of cold, oxygenated water (i.e., oxythermal habitat) available to Lake Whitefish, the most sensitive coldwater species present in this lake (Cisco are also present). Lake Whitefish require a layer of oxythermal habitat that contains water temperatures below 17.2 degrees C (63.0 degrees F) and dissolved oxygen concentrations above 3.0 mg/L. Based on the profile from the deepest basin, the water temperature decreased to below 17.2 degrees C (63.0 degrees F) at 24.5 feet and the dissolved oxygen concentration decreased to 3.0 mg/L at 23.7 feet at the time of sampling. The water column did not contain a layer of water with sufficient temperature and dissolved oxygen for Lake Whitefish.
\n
\nFurther, the temperature at which dissolved oxygen decreased to 3.0 mg/L (i.e., TDO3, a single variable to characterize oxythermal habitat) was 17.9 degrees C (64.3 degrees F). TDO3 values near 17.2 degrees C (63.0 degrees F) indicate that oxythermal conditions were unsuitable for Lake Whitefish at the time of this survey.
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\nData collected by the Minnesota Department of Natural Resources in 2011-2023 during the late summer thermal stress period, indicate suitable oxythermal habitat in all years surveyed, in contrast with 2024. When inadequate oxythermal habitat is available, Lake Whitefish are squeezed into unfavorable, warmer water conditions and experience higher levels of stress.
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