The migratory patterns of Gulf sturgeon, Acipenser oxyrinchus desotoi, within the Pascagoula River drainage and potential influences on its behavior
Gulf sturgeon are large, anadromous fish, with adults moving into rivers in early spring for spawning and returning to the marine environment in late fall. Gulf sturgeon are federally listed as threatened, with the principal reasons for population declines being habitat loss due to dams, overfishing, and water quality deterioration. The overall objective of this dissertation was to further our understanding of Gulf sturgeon life history with emphasis on their migratory behavior in order to facilitate their recovery and management. To do this we captured, radio-tagged, and monitored movement of Gulf sturgeon in the Pascagoula River drainage from 1997-2002. Gulf sturgeon migrate from the coast to the Bouie River north of Hattiesburg, Mississippi for spawning (250 river kilometers upstream from the mouth of the Pascagoula River). Spawning was verified through the collection and rearing of eggs in April of 1998 and 1999; eggs were collected in an area that consisted of hard substrata, gravel, and turbulent, high flow. We documented that from May to November Gulf sturgeon congregate in the lower portion of the Pascagoula River and Big Black Creek before they return to the Gulf of Mexico. Gulf sturgeon initiated their migration out of fresh water from late-September to mid-October, coinciding with water temperatures falling below 21 to 26°C (× ÃÑ = 23.7) and streamflow was typically higher than during summer. We captured a total of 251 Gulf sturgeon (including within and among year recaptures). Using the program CAPTURE, we estimated the population size in 1999 as 193 individuals and 206 individuals in 2000. We used an enzyme-linked immunosorbent assay (ELISA) to detect vitellogenin from blood samples to determine gender and reproductive status of Gulf sturgeon. Plasma vitellogenin levels from 11 known males were 13.0-86.0 μg/ml. We identified 43 Gulf sturgeon as female based on high vitellogenin levels (>100 μg/ml); female plasma vitellogenin levels were 110.1-7,634.2 μg/ml. We assessed the costs and benefits of Gulf sturgeon inhabiting freshwater and saltwater environments to gain insight into their migratory behavior. Throughout this dissertation we compared our data with other studies to assess population status and behavior of Gulf Sturgeon in the Pascagoula River drainage.