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Stock characteristics of Lake Whitefish in Lake Michigan
Brian Sloss1, Matthew Belnap2, Justin VanDeHey1
1 College of Natural Resources, University of Wisconsin-Stevens Point
2Wisconsin Cooperative Fishery Research Unit, College of Natural Resources, University of Wisconsin-Stevens Point
Lake whitefish Coregonus clupeaformis support important recreational, commercial, and tribal fisheries in the Great Lakes, including Lake Michigan. Genetic analyses indicate at least six distinct lake whitefish stocks exist in Lake Michigan, resulting in a mixed-stock fishery. Biological characteristics could vary among genetic stocks, but these differences may not be accounted for in current monitoring efforts that rely on capture location to assign fish to individual stocks. Our objectives were to determine if: 1) stock assignments of lake whitefish based on October capture location in Lake Michigan were accurate; 2) weight-length relationships, growth, age structure, and measures of reproductive investment (i.e., gonad weight, fecundity, and egg diameters) differed among genetic stocks of lake whitefish in Lake Michigan and 3) if biological metrics estimated using capture location for stock assignment were within ± 10% of metrics estimated using genetics for stock assignment. Accuracy of stock assignments based on October capture location varied among management zones and genetic stocks. Only 1 or 2 genetic stocks were collected at each capture location during October; when two stocks were collected, they were considered geographically proximal and were generally similar in terms of the biological characteristics we measured. With few exceptions, biological metrics estimated using capture location for stock assignment were within ± 10% of metrics estimated using genetic stock assignment. Stock assignments based on October capture location appear useful for describing the biological characteristics of specific genetic stocks of lake whitefish, but using October capture location alone is not sufficient to determine stock abundance and stock-specific contributions to harvest within each management zone throughout the year. Observed differences in age structure, growth trajectories, and fecundity among stocks suggest that stocks could respond differently to exploitation. Future analyses are needed to determine how stocks would respond to changes in exploitation.