Walleye Genetic Characterization in the Northern Ceded Territory of Wisconsin: Implications for Stocking Using Conservation Strategies

Abstract

AbstractGenetic diversity is a vital consideration for fisheries management, and in Wisconsin, it has been an explicit goal to preserve the genetic integrity of naturally recruiting Walleye Sander vitreus populations. It is unknown whether current management areas reflect the current genetic structure of naturally recruiting Walleye in the Northern Ceded Territory (NCT; approximately the northern third of the state). Our objectives were to test whether significant genetic structure exists among the NCT naturally recruiting Walleye and compare that genetic structure to current watershed management areas. We used 10 microsatellite loci to determine Walleye genetic structure through genetic stock identification. Walleye (N = 1,239) were genotyped from 25 sample locations distributed throughout the NCT. Genetic differentiation was estimated by calculating pairwise measures between sample locations using the fixation index GST and the differentiation index Dest. Admixture and no‐admixture models were used in STRUCTURE to find estimated sample location groupings. Analyses identified four groups with an east–west divide and two additional independent groups. These genetic groups generally conformed with geographic location in the NCT and current watershed management areas in Wisconsin (N = 6). Some discrepancies between genetic characterization of sample locations and watershed management areas did exist. The Green Bay (easternmost) watershed management area sample was not found to be genetically distinct from the upper Wisconsin River basin sample locations. Wisconsin glacial recession is a likely determinant of genetic structure in NCT Walleye. Postglacial geological events and historical stocking events across watershed boundaries may have influenced some of the current genetic structure observed in the upper Wisconsin and upper Chippewa River headwaters, with the genetic grouping of Millicent Lake and Willow Flowage having consistent genetic characterization. Maintaining genetic integrity within management activities (e.g., propagation programs) will help to maintain and support the long‐term stability of naturally recruiting Walleye in the NCT of Wisconsin.