Spatial and Temporal Genetic Patterns Among Walleye Spawning Groups: A Fine-Scale Analysis in Lake Erie

Defining genetic stocks of walleye (Sander vitreus) and understanding their spatial and temporal patterns may provide critical data for conservation and management. We test the genetic composition of Lake Erie walleye spawning runs (1) spatially from 11 primary spawning sites, (2) temporally from the 1995-2010 runs at 3 sites, (3) between the sexes, (4) among age cohorts, (5) across the temporal course of an individual run, and (6) between larval versus adult gene pools. We analyze a total of 1213 individuals using 9 nuclear microsatellite loci with pairwise divergence tests, AMOVA partitioning, Mantel tests, 3-D factorial correspondence, and Bayesian assignment tests. Results show that (1) most spawning sites genetically diverge, with those along the southern lake shore more similar, especially the Maumee and Sandusky River runs in the western basin, (2) the genetic composition within walleye runs is mostly consistent, with some annual stochasticity, (3) patterns do not differ between sexes, (4) there is no significant difference among age cohorts, and (5) there are no differences in early versus late-run fish at a given site. Preliminary analyses of (6) larval and adult walleye genetic composition show that larvae sampled on April 19, 2010 significantly varied from adults sampled on April 15. However, larvae sampled on May 10, 2010 genetically matched the April 15 adults, which had spawned ~20 days before and were the likely parental group. Our study thus shows that a single year “snapshot” of walleye spawning groups may not adequately characterize their overall genetic connectivity and divergence patterns, illustrating the importance of understanding temporal and spatial stock structure to assist fisheries management.