Genetic Assessment of Population Structure of Siscowet Lake Trout Salvelinus namaycush siscowet in Lake Superior

Siscowet lake trout (Salvelinus namaycush siscowet) are a deepwater form of lake trout native to Lake Superior, and represent the only deepwater form of lake trout that has not been extirpated from the Great Lakes. Because of the vast amount of deepwater habitat present in Lake Superior, siscowet are the most substantial predator in the lake.  Although there are no commercial fisheries that presently focus on siscowet lake trout, there is interest in targeting this species for a fish oil fishery. As reliable identification of stock structure is a cornerstone to sustainable fisheries, understanding the spatial structure of siscowet in Lake Superior is essential for their sustainable management. We used 17 microsatellite loci to examine the genetic diversity and population structuring of siscowet lake trout throughout Lake Superior. The results confirm that the siscowet morphotype is genetically distinct from lean lake trout, and showed no evidence of interbreeding between the two forms. Remarkably, we found no evidence of genetic pattern or stock / population structuring within siscowet despite a high degree of geographic distance between sampling sites. These results suggest that siscowet lake trout represent a single panmictic population throughout Lake Superior. Appropriate management and harvest strategies should therefore be developed to reflect shared harvests and management responsibilities for the single, multijurisdictional population of siscowet throughout the entire lake, rather than individual management strategies based on geographic location.