Cooperative Fish and Wildlife Research Units Program: Wisconsin Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

Wisconsin Fishery Project

Contemporary Stock Sturcture of Muskellunge Populations in Northern Wisconsin

June 2007 - July 2010


Participating Agencies

  • Wisconsin Department of Natural Resources

Wisconsin has more than 700 muskellunge (Esox masquinongy) populations providing a diverse array of angling experiences from high-density action waters to lowdensity trophy fisheries. The Wisconsin Department of Natural Resources’ (WDNR) muskellunge management goals include maximizing angling opportunities while preserving genetic integrity. The WDNR manages muskellunge populations through regulations, such as daily bag limits and length limits, and a prolific stocking program. Supplemental stocking can have strong impacts on the genetic integrity of any population. The WDNR currently delineates muskellunge management units based on watershed boundaries. The goal of this study was to resolve the genetic structure of native muskellunge populations in northern Wisconsin. Specifically, the objective was to delineate and compare contemporary genetic structure and current management units to determine if they were congruent. Non-lethal fin clips from 43 naturally recruiting populations (n ≈ 50/population) across the native range of muskellunge in Wisconsin were collected. Samples were genotyped using a suite of 14 microsatellite loci. Bayesian analysis was used initially to remove populations that showed significant signs of admixture resulting from previous stocking events. Genetic stock identification (GSI), a hierarchical process for determining genetic structure across a landscape that incorporates genic differentiation, cluster analyses, and analysis of molecular variance (AMOVA), was used to delineate genetic structure. Analysis of 39 populations using GSI identified 30 unique gene pools in the dataset. Because of the limitations of managing for this many genetic units, we identified putative management units as cluster scenarios where the ratio of among-group variance (Va) to within-group variance (Vb) was greater than one. This approach identified three groups corresponding to a Wisconsin River Genetic Unit, upper Chippewa River Genetic Unit, and inner Chippewa River Genetic Unit. Although these units don’t strictly adhere to current watershed basins, they do represent geographically cohesive groups. Both geographical (headwater capture following glacial recession) and anthropogenic (supplemental stocking) effects can logically explain the observed genetic structure. Further research should help elucidate the underlying processes responsible for the current genetic delineation.