RADseq of Cisco (Coregonus artedi) from drowned river mouth lakes connected to Lake Michigan

Characterizing seasonal fish movements is a prerequisite to understanding trophic structure and can inform fisheries management. Drowned river mouth lakes (DRMs) are productive inland habitats connected to Lake Michigan that play seasonal roles for migratory fishes. Despite growing recognition of their ecological connections to the Great Lakes, for many fishes the value of DRMs as seasonal habitats is not well understood. One such species, cisco Coregonus artedi, has expanded in the 21st century from near lakewide extirpation to high relative abundances in northeastern Lake Michigan. Cisco have also been reported in DRMs along the eastern shoreline >270 km apart in the winter, but little is known about cisco movement patterns and ecology in these systems and their connections to the northeastern Lake Michigan spawning stock. In winter 2022 and 2023, we collected cisco from three DRMs along the eastern shores of Michigan (Lake Charlevoix, Portage Lake, Muskegon Lake) to examine genetic, morphometric, and diet differences. We also implanted telemetry tags in 20 cisco collected in Lake Charlevoix to examine seasonal movement patterns and determine whether they are residents of the DRM or seasonal migrants from Lake Michigan. We found no evidence of genetic or morphometric differentiation across DRMs, suggesting that recolonization began from a single remnant stock. Winter diets consisted entirely of fish, with alewife as the most common diet item. Movement patterns over two years indicated strong spawning and non-spawning site fidelity and that cisco overwintered in Lake Charlevoix for at least six months. Our results improve our understanding of the biocomplexity of the Lake Michigan cisco fishery which can inform recreational harvest regulations and aid in future conservation planning.