Evaluation of stock assessment methods for commercial walleye (Sander vitreum) Fishery of Red Lakes, MN.

Abstract

In 1997, the Red Lakes walleye (Sander vitreus) fishery was closed due to extremely low population numbers and a massive rehabilitation program was started for the walleye in 1998, by tribal, state and federal authorities, because of the ecological, economic, and cultural importance of the walleye fisheries. Management authorities recognized that a stock assessment of some manner would be necessary to monitor the reopened fishery if it were to be maintained on a sustainable basis. However, it would be necessary to choose from a variety of methods, ranging in complexity from an index of abundance to an age-structured method such as a statistical catch-at-age model. The primary goal of this research is to examine different types of models that may be appropriate for use in the fishery and determine how they may perform when used for the Red Lakes fishery. A secondary goal was to determine if a simulation of potential unaccounted for catch or if previous research into annual growth factors might improve the predictive capability of the delay-difference model. This research found that generally, the age-structured models performed better than the delay-difference model, the inclusion of the walleye environmental coefficients improved the fit of the delay-difference model, the assumed black market catch resulted in only limited improved fit of the delay-difference model with general increases in fishing effort, and the environmental coefficients had limited explanatory power in changes in population abundance.