Habitat heterogeneity has the possibility of structuring populations. Even in connected landscapes there is usually cryptic structuring of populations that often coincides with landscape features that inhibit gene flow or select for phenotypes. Yellow perch (Perca flavescens) is an economically and ecologically prominent fish in the Laurentian Great Lakes. In the Lake Michigan basin, yellow perch reside in coastal habitats of Lake Michigan and drowned river mouths (habitats that link tributaries to Lake Michigan). Management agencies in this area are especially interested in yellow perch populations since yellow perch suffered dramatic declines in recruitment in the late 1980s and have since remained at lower abundance than their historic average. The goal of this study was to understand how yellow perch populations are structured in eastern Lake Michigan. Specifically, we wanted to test whether there was genetic heterogeneity that coincides with habitat heterogeneity by sampling drowned river mouths and nearshore Lake Michigan. We sampled yellow perch from 10 drowned river mouths in both deep and littoral habitats (spring, summer, and fall) and two nearshore sites in Lake Michigan (spring and fall) during 2015-2016.
We found shallow but significant genetic population structure between drowned river mouths based on pairwise FST and STRUCTURE analyses. However, the pattern of genetic population structure is complex and does not support the hypothesis of isolation by distance, where populations in nearby drowned river mouths are more genetically similar than populations further apart. For instance, one drowned river mouth in particular (Pentwater) was distinct from the other drowned river mouths in all analyses and was located toward the middle of our sampling sites that spanned a north-south gradient along Lake Michigan’s shoreline. We are currently conducting additional analyses to explore how populations of yellow perch from Lake Michigan compare with populations from drowned river mouths. However, our preliminary results suggest that yellow perch in Lake Michigan drowned river mouths are not a panmictic population but rather consist of multiple populations within complex connected habitats. We recommendnd that fisheries managers recognize this diversity when setting harvest regulations.