Interactions of Anglers and Walleyes in Escanaba Lake, Wisconsin

Abstract

Interactions of anglers and walleyes (Stizostedion vitreum vitreum) were analyzed by fitting difference equations to a 33—yr time series from Escanaba Lake, Wisconsin. Fish population dynamics were density—dependent, and harvest by anglers followed a sigmoid functional response. The deterministic form of the model was stable and suggested that the fishery could withstand relatively high exploitation rates. The stochastic form of the model compared management strategies using the probabilities of increased or decreased fish and angler populations and the probability that fish populations will fall below a threshold level. These calculations exposed high risks associated with management strategies based on deterministic, equilibrium equations. The probabilities of sustaining both the fish stock and angler effort increase if harvest rates are reduced below the optimum derived from deterministic models. Consideration of angler dynamics reduced the prediction error of fish stock forecasts and substantially altered risk assessments and management recommendations. If angler dynamics were ignored, the optimal exploitation rate and the risk of overfishing would be overestimated. Lake sport fishery assessments can be improved by coupling models of fish dynamics at the scale of individual lakes with angler models at the larger scale of lake districts.