An Evaluation of Walley Survey Methods in the Ceded Territory of Northern Wisconsin

Abstract

Federal court rulings affirmed the rights of Chippewa tribes to fish off reservations in the northern third of Wisconsin. The J1h District Federal Court ordered a management system to allocate the available harvest of walleye Stizostedion vitreum to tribes and anglers based on total allowable catch limits (TACs) for tribal spearing and sliding bag limits for angling. Regulations for inland lake walleye are based on spring mark-recapture population estimates in northern Wisconsin. The Wisconsin Department of Natural Resources (WDNR) estimated walleye abundance in 22-43 lakes per year during 1990-2000. My objective was to evaluate current sampling protocols to maximize the efficiency of sampling. I used exponential models, errors-in variables models and multiple regression models to test the linearity of the relationship between electrofishing catch-per-effort and walleye density, effects of measurement errors, and factors that contribute to variability in the relationship. Results showed a nonlinear relationship between catch rates and walleye density, measurement errors were greater in catch rates than density estimates, and catchability of walleyes to electro fishing is affected by conductivity and population density. I concluded that electrofishing catch-per-effort may be used to index walleye densities at low catch rates, but should be cautiously to index walleye densities at high catch rates in northern Wisconsin lakes. I also quantified the relationship between recapture rates from electrofishing and tribal spearing and electrofishing and angling using a linear model. I found that electrofishing and spearing recapture rates and electrofishing and angling recapture rates were not significantly related in most cases. I found a significant relationship between spearing recapture rates and electrofishing recapture rates of adult walleyes, which indicated that spearing recaptures might be useful to estimate adult walleye abundance. I also found a significant relationship between angling recapture rates and electrofishing recapture rates of total walleyes, which indicated that angling recaptures might be useful to estimate total walleye abundance. I concluded that the lack of significant relationships between recapture rates in electrofishing and spearing and electrofishing and angling prevents the use of spearing or angling recapture rates to estimate walleye abundance in most cases, however further research into the biases of spearing and angling recaptures may allow the use of spearing and angling recaptures to estimate adult and total walleye abundances.