Two Distinct Life History Strategies of Atlantic Sturgeon in the Ogeechee River, Georgia

Abstract

Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) is an anadromous, widely distributed, highly migratory sturgeon subspecies that occurs in rivers and marine waters along the North American Atlantic Coast. This fish has shown widespread declines and has been afforded conservation protections, including some based in the U.S. on the delineation of Distinct Population Segments (DPS) under the Endangered Species Act. The management of Atlantic sturgeon will benefit from the knowledge of its population structure as well as the ability to uniquely identify individuals (in relation to population origin) that are vulnerable to anthropogenic stressors at sites outside of their natal estuaries. We used microsatellite analysis to estimate the genetic population structure of Atlantic sturgeon from 13 spawning rivers ranging from the St. Lawrence River, Quebec to the Satilla River, Georgia. Individual Based Assignment (IBA) testing was used to estimate the contribution of each population to mixed-stock aggregations in coastal waters and in a non-natal estuary. An unexpected finding was the discovery of two distinct genetic clusters of juvenile Atlantic sturgeon in the Ogeechee River, Georgia, with specimens in the two clusters differing significantly in terms of mean total length. Additionally, three distinct genetic clusters were detected within the Satilla River juvenile collection, along with two clusters within the Edisto River sample. In F1ST and FST analyses, the extent of the pairwise genetic differentiation between the two genetic clusters in the Ogeechee River and the three in the Satilla River was greater than that between all other pairwise comparisons among rivers in the South Atlantic DPS. In contrast, we found no evidence of the genetic partitioning of juvenile sturgeon within the neighboring Savannah or Altamaha river populations. Using IBA, we found that the overall Ogeechee River population made a moderate contribution (8.3%) to the overall mixed-stock collections (n = 1512) from coastal North Carolina to the Bay of Fundy. Surprisingly, all of the Ogeechee River-assigned specimens (n = 125) in these mixed-stock aggregations were representatives of only one of the two Ogeechee River genetic clusters. These results suggest that the two Ogeechee River genetic clusters exhibit significantly different life history strategies, with one being resident and the second being highly migratory.