Genetic evidence for relict Atlantic sturgeon stocks along the mid-Atlantic coast of the USA

The Atlantic sturgeon Acipenser oxyrinchus oxyrinchus is a highly migratory anadromous acipenserid that is distributed along the Atlantic coast of North America. The abundance of Atlantic sturgeon has not increased appreciably in recent years despite the imposition of a moratorium on its harvest in U.S. waters in 1998. Two measures being considered to restore depleted or extirpated populations are designation of Atlantic sturgeon as federally endangered under the U.S. Endangered Species Act and the use of hatchery-reared fish to supplement natural reproduction. Implementation of these approaches requires detailed knowledge of this species' population structure. Previous genetic stock identification studies failed to address the discreteness of Atlantic sturgeon populations along the U.S. mid-Atlantic coast that historically supported two of the largest fisheries for the species. We used mitochondrial DNA (mtDNA) control region sequence data to elucidate the population structure of Atlantic sturgeon in the Delaware River and two tributaries of Chesapeake Bay, the James and York rivers. Haplotypes of individuals from these rivers were compared with those from 14 other estuaries. Levels of mtDNA diversity were moderately high; 45 haplotypes were observed among the 860 specimens analyzed. We found significant temporal instability of haplotypes among collections of subadults made in different years from the Delaware River, including haplotypes not seen elsewhere and others that were common in the adjoining Hudson River and Albemarle Sound. Ibis finding suggests that natural reproduction of a genetically distinct population still occurs in the Delaware River, but that it also hosts migrant subadults from elsewhere. In contrast, temporal instability of haplotype frequencies was absent among collections from different years in the Hudson River. Although private haplotypes were absent from the James and York River samples, significant frequency differences between these collections and those from elsewhere suggest that some tributaries of Chesapeake Bay still host genetically unique populations of Atlantic sturgeon.