Forecasting Effects of Harvest Regulations and Stocking of Walleyes on Prey Fish Communities in Lake Mendota, Wisconsin

Abstract

Two commonly used simulation models were combined to assess the effects of stocking and harvest regulations on the consumption dynamics of walleyes Stizostedion vitreum in Lake Mendota, Wisconsin. An age-structured population model was used to estimate the effects of five harvest scenarios on walleye population and fishery characteristics. Implementation of a 15-in minimum size limit resulted in increases in total yield (by weight), average weight of fish harvested, and walleye biomass remaining in the lake, Changes in walleye age structure resulting from various harvest scenarios were used as inputs to an energetics model to estimate how prey consumption by walleyes would vary under different harvest regulations. Simulations indicated that a stocking program that produced 8,000 yearling recruits annually would double walleye predation on planktivorous fish compared with predation estimated in 1987, when the study began. The modeling further indicated that a 15-in minimum size limit in conjunction with a stocking program would triple predation rates. This increase would be sufficient to reduce recruitment of yellow perch Perca flavescens in Lake Mendota in most years. Combining these two modeling techniques provides a framework for fishery managers to forecast how prey populations might respond to harvest regulations for gamefish.