Habitat Use and Movements of Juvenile Shortnose Sturgeon in the Savannah River, Georgia-South Carolina

Abstract

During 1999-2000, 28 juvenile (<56 cm total length) shortnose sturgeon Acipenser brevirostrum were captured in the lower Savannah River, Georgia−South Carolina, and acoustic transmitters were implanted in or attached to 15 of them. The juveniles were located only between river kilometers (rkm; measured from the mouth of the river) 31.2 and 47.5, in salinities of 0.1‰ to (briefly at high tide) 17.6‰, and at depths of 2.1-13.4 m. The fish used two small areas very intensively. When water temperatures were above 22°C, the fish moved upriver; they aggregated particularly at rkm 47.5 when temperatures were greatest, and the average salinity at this location was 0.1‰. When water temperatures were below 22°C, the fish moved downriver into Savannah Harbor and used approximately 2-km segments of the Front and Middle rivers just upriver of their confluence at rkm 31.5. Here they encountered higher salinities (mean, 5.4‰) than during warm months. During the period of lowest water temperatures, the fish aggregated just inside the mouth of the Middle River in a hole separated from the deeper Front River by a sill. Movements related to tide stage or diel phase were not observed. Fish carrying transmitters with a depth option were always located on or near the bottom (±1.5-m transmitter accuracy). No juveniles were recorded as far downriver as the nursery area identified in a study conducted about a decade earlier, perhaps due to changes in hydrographic conditions that were induced by harbor modifications. The cool-season habitat is in the portion of the harbor to be impacted by further modifications. The relative abundance of juveniles suggests that recruitment has not increased despite an apparent increase in the adult population from the stocking of hatchery-reared fish during 1985-1992.