Historical genetic connectivity of lake sturgeon in a dammed Great Lakes tributary

Abstract

Lake sturgeon (Acipenser fulvescens) populations are the focus of rehabilitation efforts across the Great Lakes. Although historical fisheries were a major cause of population collapses, habitat fragmentation and/or loss and reduced access to spawning and juvenile habitat impose contemporary challenges for population recovery. The loss of connectivity between habitat types required by different life stages may particularly limit recruitment rates, inhibiting population increase towards recovery targets. We used microsatellite DNA genotyping to assess population structure, diversity, and historical connectivity of lake sturgeon in the Black Sturgeon River watershed, a major tributary of Black Bay, Lake Superior with both historical and contemporary dams. Genotype data from lake sturgeon sampled above and below an existing major barrier, as well as from lakes in the upper watershed, showed evidence of historical connectivity throughout the watershed. Despite the existing barrier fragmenting the river and preventing upstream migration, lake sturgeon from the Black Sturgeon watershed showed clear membership to a single ancestral gene pool. Estimates of genetic effective population size (Ne) for the above- and below-barrier population segments were reduced compared to the larger (watershed level) gene pool. Although the longevity of lake sturgeon has largely enabled the retention of historical genetic diversity for the population in the watershed, the reduced productive capacity of this significant tributary may have implications for recovery rates for the regional Lake Superior metapopulation. Restoring connectivity among habitats would benefit the long-term conservation and management of this species throughout this river system, and potentially the regional metapopulation.