Bioenergetics Modeling as a Salmonine Management Tool Applied to Minnesota Waters of Lake Superior

Abstract
Lake Superior's fish community has undergone dramatic changes since the mid-1950s, with major shifts in the forage base, invasion of exotics, and decline of lake trout Salvelinus namaycush. Predator species have been introduced, and many of these are maintained by stocking. The impact of these stocked fish on the forage base and the ability of the forage base to sustain projected stocking levels are unknown. Bioenergetics modeling is a particularly useful tool for coordinating data to answer questions about predator–prey dynamics, stocking quotas, and forage requirements. This study focused on the Minnesota waters of Lake Superior to gain perspective on the impact of fish stocked by Minnesota and to serve as a basis for future expansion of the analysis to all parts of the lake. The objectives of this study were to compile data on the major salmonines in Minnesota waters of Lake Superior for use in a bioenergetics model, to estimate salmonine predation on prey populations through modeling simulations, and to prioritize data needed for future input to the bioenergetics model. Estimates of consumption by predator stocks in 1989 totaled 3,047 metric tons of rainbow smelt Osmerus mordax and 401 metric tons of coregonines, which greatly exceeded estimates of biomass plus production of prey species. Underestimation of prey fish biomass probably accounts for most of this discrepancy. Recent shifts in the forage base, heavy predation on prey species by stocked fish, and reduced survival of stocked chinook salmon Oncorhynchus tshawytscha suggest that caution should be exercised in future stocking. Further data acquisition should focus on determining prey fish biomass and production, predator age and growth, predator diets, predator population abundances, and mortality rates.

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