Predicting fish production from lake size using novel measurement strategies of fish behavior

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Freshwater fish are an exceptionally important resource to Canadians. Disturbingly, recent research demonstrates some recreational fisheries are suffering from hidden collapses; fish production (i.e. the amount of new tissue generated per area per year) is declining while harvest (kg yr-1) remained constant, leading to overharvest. Fisheries closure due to declining production and overharvest is an enormous economic and cultural threat to Canadians and indigenous peoples, and to global society as a whole. Currently, however, whether fish production is declining across Canada's inland lakes remains unknown. Warming global temperatures that affect fish habitat also remain a looming uncertainty for fish production and sustainable harvest into the future. A major knowledge gap facing fisheries managers is how fish habitat use and production change predictably through time (seasonally and interannually) and from small to large lakes. The partnership between 4 Universities and the Ontario Ministry of Natural Resources and Forestry (OMNRF) will address this knowledge gap by using an easily measured variable, lake size, to predict fish habitat use and production. To do so, we will generate highly resolved data on fish habitat use (i.e. position in the lake) and diet, using acoustic telemetry and stable isotopes, in 3 co-occuring species of recreational and cultural value: lake trout (Salvelinus namaycush), cisco (Coregonus artedi), and smallmouth bass (Micropterus dolomieu). Our novel approach will, for the first time, quantify habitat and diet overlap among 3 species throughout all seasons and across 5 years in a small, intermediate and large-sized lake, simultaneously. The results will provide fisheries managers with an unprecedented ability to predict fish habitat use and production from easily measured lake characteristics. Our findings will shed fundamental new light on the importance of seasonal variation, including poorly studied winter periods, in structuring species interactions and shaping fish behavior across a lake size gradient. The results will lead to new fisheries management methods and policies that will be applied broadly Canada-wide to benefit all Canadians by helping protect freshwater fishes into the future.