Defining Spawning Stock Structure of Great Lakes Fishes: Examples from Walleye, Yellow Perch, and Smallmouth Bass

The genetic stock structure of three popular Great Lakes fishes from two families: walleye Sander vitreus (Percidae), yellow perch Perca flavescens (Percidae), and smallmouth bass Micropterus dolomieu (Centrarchidae) is examined in light of the definition: “Fishery stocks are population subunits that interbreed freely in given geographic locations, share a common gene pool, and differ significantly from other subunits” (Hallerman et al. 2003). We compare and contrast broad- versus fine-scale spatial and temporal stock structure patterns from spawning groups using nuclear DNA microsatellite loci and mitochondrial DNA control region sequences, with a variety of population and landscape genetic approaches.  We analyze hierarchical patterns across their native North American ranges, the Great Lakes, and within Lake Erie. The three species have varying levels of genetic diversity, with walleye having the highest heterozygosity levels, followed by smallmouth bass, then yellow perch. Genetic divergence patterns follow the opposite trend, with the most pronounced differences occurring among closely spaced spawning groups of yellow perch, smallmouth bass, and then walleye; all show considerable genetic structure across their ranges and similar patterning of discontinuities among geographic regions. Results reveal that fine-scale stock structure does not correspond to isolation by distance hypothesis, with pronounced genetic differences found among some closely-spaced spawning groups. Genetic composition of spawning groups is stable from year to year in walleye, according to two decades of data, and less consistent in yellow perch.  We relate life history and behavioral differences of the three species to regulation of their respective stock structures.