Human impacts on Great Lakes walleye Sander vitreus structure, diversity, and local adaptation

Artificial propagation and wild release may influence the genetic
integrity of wild populations. This practice has been prevalent in
fisheries for centuries and is often termed “stocking”. In the Laurentian
Great Lakes (Great Lakes here-on), walleye populations faced declines from
the 1950s to the 1970s, prompting extensive stocking efforts for
restoration. By the mid-2010s, walleye populations showed signs of
recovery, but the genetic legacy of stocking on population structure at
the genomic level remains unclear. Using a dataset of 45,600
genome-aligned SNP loci genotyped in 1,075 walleye individuals, we
investigated the genetic impacts of over 50 years of stocking across the
Great Lakes. Population structure was associated with both natural
geographic barriers and stocking from non-native sources. Admixture
between Lake Erie walleye and walleye from the re-populated Tittabawassee
River indicate that stocking may have re-distributed putatively adaptive
alleles around the Great Lakes. Genome scans identified FST outliers and
evidence of selective sweeps, indicating local adaptation of spawning
populations is likely. Notably, one genomic region showed strong
differentiation between Muskegon River and walleye from the Tittabawassee
River which was re-populated by Muskegon strain walleye, suggesting
admixture and selection both impact the observed genetic diversity.
Overall, our study underscores how artificial propagation and
translocations can significantly alter the evolutionary trajectory of
populations. The findings highlight the complex interplay between stocking
practices and population genetic diversity, emphasizing the need for
careful management strategies to preserve the genetic integrity of wild
populations amidst conservation efforts.