Angling Effects on Abundance of Preferred-Size Bluegill in Northern Wisconsin Lakes

Bluegill populations in northern lakes are often plagued by a lack of quality, but some waters are able to sustain high numbers of preferred-size fish.  We hypothesize that angler harvest is an important driver of among-lake differences in bluegill size structure.  We compare population metrics of bluegill spawning populations among 3 northern Wisconsin Lakes.  Annual angler harvest was estimated to be 19.7 bluegill per acre in Manson Lake, 15 per acre in Roy Fredrich Lake and 0 per acre in Blair Lake.  The relative abundance of bluegill in Manson Lake was 65 bluegill per fyke net and less than 1.0% of bluegill captured were > 8.0 inches.   We estimated a bluegill population using mark-recapture methods in Roy Fredrich Lake of 162 fish/acre (catch of 81 bluegill per fyke net) and 19% of bluegill captured were > 8.0 inches. The bluegill population of Blair Lake was estimated at 183 per acre (catch of 106 bluegill per fyke net) and 56% of bluegill captured were > 8.0 inches. In Manson Lake, only 3.0% of an aged subsample were 7 years of age or older, while 61% in Roy Fredrich Lake and 70% in Blair Lake were at least 7 years of age. Length-at-age results indicate that the higher proportion of preferred-size bluegill in Roy Fredrich and Blair Lakes are the result of below-average growth over a long life-span.  Our results suggest that large fish are cropped off at higher levels of harvest, but bluegill size structure can hold up with a moderate reduction in harvest rate.