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

The Wisconsin Department of Natural Resource’s walleye (Sander vitreus) management goals include ensuring the population viability and genetic integrity of naturally recruiting walleye populations. Walleye show both broad-scale genetic (i.e., regional) and fine-scale genetic structure (i.e., watersheds). Supplemental stocking, stocking fish into systems where some level of natural recruitment occurs, is commonly employed in the management of Wisconsin walleye. Supplemental stocking can adversely affect the overall broad- and fine-scale genetic structure, population levels of genetic diversity, and lower the overall effective population size resulting in increased inbreeding and genetic drift. Previous genetic research has identified low effective population size (Ne) to census popula-tion size (Nc) ratios (approximately 3-5%) suggesting inbreeding and genetic drift should be considered important in conserving the genetic diversity of walleye populations. Additionally, significant inbreeding has been observed in a number of walleye populations thought to have healthy census populations. The first objective of this research is to determine if previously observed genetic indica-tions of inbreeding in some naturally reproducing walleye popula-tions were the consequence of sampling a small number of spawn-ing locations (and thus, a high number of related individuals) or accurate estimates of inbreeding. The second objective is to deter-mine if a relation exists between measures of walleye genetic diver-sity and observed patterns of recruitment and management activi-ties. Previously identified walleye populations that exhibited sig-nificant inbreeding coefficients were originally sampled using fyke-nets during the spawning run. In many instances, the number of nets sampled were small suggesting a potential sampling bias. Therefore, the first objective will be addressed by re-sampling the previously studied populations using shoreline electrofishing to ob-tain a larger more spatially representative genetic sample. Samples (n = 50) will be surveyed for genetic variation at 13 microsatellite loci and estimates of inbreeding and within population genetic dif-ferentiation (the Wahlund effect) will be performed. The second objective will be addressed by determining the genetic diversity of walleye populations across a gradient of management practices and recruitment levels (Npops = 14). Genetic diversity in the adult spawning population and the subsequent fall’s young of year will be surveyed. Estimates of Ne, heterozygosity, mean number of al-leles/locus, and allelic richness will be used to examined trends and relations among the diversity estimates and known recruitment and management practices. This research may provide insight into the impacts of supplemental stocking, natural recruitment variability, and spatial dynamics on the overall integrity of walleye popula-tions.