Genetic evaluation of American shad restoration success in James River, Virginia

Millions of oxytetracycline (OTC) tagged American shad larvae have been stocked into the James River from the neighboring Pamunkey River since 1994.  Hatchery returns to the James peaked in 2002, after which the number of untagged recruits began to increase indicating natural reproduction, though the origin of these recruits was unknown.  Using nine microsatellite loci, we characterized the donor (Pamunkey) and recipient (James) populations from their pre-restoration (1992, 1993) to current states (2008, 2009) to assess the genetic impact of the restoration program and to identify the origin of untagged recruits returning to James River.  Tests of genetic differentiation show frequent temporal genetic changes in both populations. Estimates of genetic diversity in both populations were high and not significantly different in comparison to pre-restoration samples, across years, or between hatchery and wild cohorts returning within any single year indicating retention of genetic diversity.  Overall population structure measured by AMOVA was low among all samples from both rivers (Ô_st = 0.0056) with the highest pair-wise comparison between James and Pamunkey 2007 (Ô_st = 0.0127).  Maximum likelihood estimates of the proportion of Pamunkey origin shad in the current James population suggest James is presently composed almost entirely of Pamunkey lineage.