Effect of Harvest Mortality on Muskellunge Size Structure in Wisconsin's Ceded Territory

Abstract

Muskellunge Esox masquinongy management is often aimed at producing large trophy individuals. However, muskellunge are a long-lived species that occurs naturally at low population densities, which makes them susceptible to the effects of harvest mortality. Muskellunge populations within Wisconsin's ceded territory are exposed to both angling and spearing fisheries. My objective was to determine the extent that harvest mortality affects muskellunge population size structure in Wisconsin’s ceded territory. Cleithra were used to estimate age and to back-calculate growth histories of muskellunge to determine the scope for growth among a range of populations producing small-, medium-, and large-bodied fish in Wisconsin's ceded territory. Female muskellunge grew larger (L∞ = 47.7 in) than males (L∞ = 40.2 in). Small-bodied populations had a mean asymptotic length of 38.7 in, medium-bodied populations had a mean asymptotic length of 45.0 in, and large-bodied populations had a mean asymptotic length of 50.4 in. These results formed the basis of an individual-based simulation model that predicted the influence of varying levels of harvest mortality from recreational angling and tribal spearing fisheries on the size structure of muskellunge populations. Both angling and spearing fisheries caused a decline in muskellunge population size structure as harvest mortality associated with either fishery increased. Numbers of trophy length muskellunge (≥ 40, 45, or 50 in) decreased as harvest mortality from either fishery increased across all body types and regulations. Combinations of angling and spearing mortality were identified that reduced relative stock density of muskellunge greater than 38 in and 42 in below levels used by the Wisconsin Department of Natural Resources to define trophy fisheries. These results can be used to aid in management of muskellunge populations in northern Wisconsin’s ceded territory by providing a series of growth standards for muskellunge populations and by identifying levels of angling and spearing exploitation that influence the trophy potential of a muskellunge population.