Effects of changes in density-dependent growth and recruitment on sustainable harvest of lake whitefish

Substantial declines in growth and recruitment of lake whitefish (Coregonus clupeaformis) and changes in key density-dependent relationships since the 1990s have raised concerns about the effects of these changes on valuable commercial fisheries in Lake Huron. There is evidence for lake whitefish in the southern main basin of Lake Huron that growth and recruitment rates have been reduced by up to 50%. Using a life history model parameterized from fishery-independent survey data for lake whitefish, we investigated the effects of declines in growth and recruitment rates on population dynamics and sustainable harvest. We evaluated a baseline scenario characterized by high growth and recruitment rates, an alternative scenario with a reduced growth rate, and another alternative scenario in which both growth and recruitment rates were reduced. Yield consistently declined by at least 71% in both alternative scenarios compared to the baseline scenario. Also, fishing became unsustainable when both growth and recruitment rates were reduced and the maximum instantaneous fishing mortality rate exceeded 0.5. Our results suggest that the recent reductions in growth and recruitment observed in Lake Huron are of sufficient magnitude to alter productivity and reduce how much can be sustainability harvested from these stocks.