Simulated equilibrium walleye densities under dynamic and constant recreational angler effort in northern Wisconsin

Recreational fishing in the United States is generally open access, so harvest is primarily determined by the amount of angler effort.  Effort is dynamic and can depend on catch rates, fish density, and other factors.  Our objective was to determine whether recreational angler effort limits walleye (Sander vitreus) population densities and what densities might result if effort was limited.  We developed a model which determined the density resulting from a given effort level or from an effort level which varied with adult walleye density.  Densities were limited by effort under the constant effort scenario, and densities were self-regulating with density dependent effort but were lower than simulations where effort was limited.  Densities ranged from 1-6 adults/acre in density dependent simulations, which is similar to the empirical estimate of 4.08 adults/acre.  Median density averaged 9.12 adults/acre when effort was zero.  Densities were generally higher with a 15-in minimum length limit compared to no length limit.  Increased post-release mortality generally resulted in lower densities.  Likelihood of extinction increased with stronger relationships between adult density and effort.  We conclude that walleye fisheries in northern Wisconsin are self regulating but persist at lower levels than would be expected with limited effort.