Temporal effective size estimates of a managed walleye Sander vitreus population and implications for genetic-based management

The goal of this research was to use the long-term fishery data set and DNA from archived scales of walleye Sander vitreus in Escanaba Lake, WI, U.S.A., to improve the understanding of the underlying mechanism(s) influencing genetic diversity in naturally recruiting populations. The introduced population of S. vitreus in Escanaba Lake has a low mean effective population size (N-E) between 124.6 and 185.5 despite a mean census size (N-C) of 4659 (N-E/N-C c. 0.04), suggesting an accelerated rate of genetic drift between 1952 and 2002. These values are smaller than the median N-E range of several studies suggesting typical N-E/N-C ratios of 0.11-0.16 in a wide range of taxa. N-E increased steadily during the past two sampled decades (1992 and 2002) and was consistent with a lowering of the variance in S. vitreus reproductive success, possibly linked to a large, sustained exploitation (mean 28%) rate. Variance in reproductive success is one of the most important factors influencing N-E in species, like S. vitreus, which have a potential for large fecundities and large juvenile mortalities (type III survivorship). The N-B estimates across six sequential cohorts (age classes of S. vitreus, assayed from 1994 to 1999) was consistent with estimates of N-E reported for 1992-2002. These results, coupled with in-depth census and exploitation data, show that the genetic characteristics of Escanaba Lake S. vitreus have changed substantially and that management activities, such as supplemental stocking and harvest practices, have profoundly influenced the genetic dynamics of S. vitreus in this lake.