Exploring optimal walleye exploitation rates for northern Wisconsin Ceded Territory lakes using a hierarchical Bayesian age-structured model

Abstract

We assessed population dynamics of walleye (Sander vitreus) in multiple Ceded Territory lakes, which support recreational and tribal fisheries, using a hierarchical Bayesian age-structured model. We used distributions of parameter estimates to develop a dynamic simulation model to forecast performances of walleye fisheries across these lakes under alternative recreational and tribal fishing scenarios. Application of a hierarchical approach allowed us to obtain more accurate estimates of stock–recruitment relationships, natural mortality, maturity and selectivity schedules, and growth parameters for individual lakes, especially for those with relatively uninformative data, and to characterize their variability among lakes. Using standing spawning stock biomass, recreational and tribal harvest, and probability of population collapse as performance metrics, our simulations suggest that northern Wisconsin walleye populations can sustain a regional optimal exploitation rate of about 20% on average given the existing recreational and tribal gear selectivities. However, lake-specific optimal exploitation rates may be higher or lower depending on estimated lake productivities, suggesting that effective management of the Ceded Territory walleye fisheries should account for variability in population dynamics among lakes.