Genetic Population Structure and Mixed-Stock Analysis of Walleyes in the Lake Erie–Lake Huron Corridor using Allozyme and Mitochondrial DNA Markers

Abstract

We used allozymes and mitochondrial DNA (mtDNA) restriction fragment length polymorphisms to determine if spawning populations of walleyes Stizostedion vitreum from the Lake Erie-Lake Huron corridor are genetically differentiated and to estimate their contributions to a commercial fishery in southern Lake Huron (operated by Purdy Fisheries) in 1994 and 1995. Both types of genetic markers detected significant differentiation among walleyes collected from different sites, suggesting that fish from Lake Erie, Lake St. Clair, and Lake Huron are not a single, genetically homogeneous population. The combined use of both marker systems detected the greatest differentiation in pairwise comparisons of samples. Although some exceptions were detected, both marker types suggest a relationship between geographic proximity and genetic differentiation. The fish from Purdy Fisheries caught throughout 1994 had highly significantly different haplotype frequencies (mtDNA) but not allele frequencies (allozymes) from those caught throughout 1995. The estimated contributions of walleyes from different spawning sites to the catch from Purdy Fisheries varied little between years. Most estimates were significantly greater than zero, indicating that all sites contributed at some level and none should be ignored in management considerations. The mixed-stock analysis was robust when factors affecting bias and precision were evaluated. * Corresponding

An improved method for predicting the accuracy of genetic stock identification

“…Mixture proportions in the fishery are then estimated using conditional maximum likelihood (Milner et al 1981;Fournier et al 1984;Millar 1987), unconditional maximum likelihood (Smouse et al 1990), or Bayesian Masuda 2001, 2006) methods that relate the genotypes in the mixture to the expected genotype frequencies in the baseline populations. Most applications of this sort of genetic stock identification (GSI) have involved Pacific salmon, but the basic methodology has now been applied to a wide range of other species as well (Waldman et al 1997;McParland et al 1999;Koljonen et al 2005).…”

Role of genetic markers in fisheries and aquaculture: useful tools or stamp collecting?

“…However, our experience with walleye (Stizostedion vitreum) (McParland 1996) and that of others (e.g., Grewe et al 1994;Wirgin et al 1997) suggest that combined analyses with both mitochondrial and nuclear markers might be recommended. For example, spawning populations of walleye from a large geographic area (Tittabawasee River, Saginaw Bay shoals in western Lake Erie) contribute to a commercial fishery in southern Lake Huron (McParland 1996). Particular spawning populations in the Lake Huron -Lake Erie corridor have been identified as especially vulnerable to overharvesting.…”

“…Particular spawning populations in the Lake Huron -Lake Erie corridor have been identified as especially vulnerable to overharvesting. The combined use of allozyme and mtDNA markers provided the most comprehensive view of population structure in walleye (McParland 1996). For example, there were several cases where one marker was successful in detecting differentiation between a pair of samples while another was not (and vice versa).…”

“…However, species with greater haplotypic diversity may show a mosaic pattern after the bottleneck due to random lineage extinction (i.e., populations will be fixed for different haplotypes). Ironically, choosing between mitochondrial and nuclear markers is counterproductive given that a combination of both in a single study often provides the most comprehensive view of population structure, possibly because of the different information content of mitochondrial and nuclear markers (e.g., McParland 1996).…”

Maturation Schedules of Walleye Populations in the Great Lakes Region: Comparison of Maturation Indices and Evaluation of Sampling‐Induced Biases

“…Presently, walleyes are harvested by both commercial and sport fisheries in Lake Erie (Knight 1997) but solely by anglers in Saginaw Bay and Oneida Lake (VanDeValk et al 2002;Fielder and Thomas 2006). Previous research suggests that walleyes in these lakes are genetically distinct (Billington and Hebert 1988;Billington et al 1992;McParland et al 1999), but the genetic distinctiveness among Lake Erie stocks is somewhat equivocal (Merker and Woodruff 1996;Strange and Stepien 2007). It is clear that these stocks display variable maturation schedules, growth, and mortality rates.…”