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Shortnose Sturgeon

Description

SturgeonSturgeons are fish of an ancient lineage easily recognized by five rows of scutes (bony plates) along their bodies: one row along the mid-back, one along the middle, and one along the lower body on each side. Sturgeons have heterocercal tails; that is, the top lobe of the caudal fin is larger than the bottom one. Coloration varies from yellowish pink to yellowish brown on the fish's back and creamy white below. Sturgeons, the largest of the bony fishes, are bottom dwellers that use chin barbels to locate food on the substrate. The barbels on the shortnose sturgeon are rather small, less than one half the width of the mouth. Sturgeons have protrusible, inferior mouths used to suck in benthic insects, crustaceans, and other food items. The shortnose sturgeon is smaller than the common Atlantic sturgeon, Acipenser oxyrinchus, and has a shorter, uncurved snout. It is also known as the blunt-nosed, round-nosed and small sturgeon, and it may grow up to 143 cm (56 in).

Habitat and Biology

Shortnose sturgeons are found from the Saint John River, Canada (New Brunswick), to the St. Johns River, Florida. They inhabit estuarine and riverine habitats and are typically not found offshore. In South Carolina they inhabit Winyah Bay Rivers, those that drain into Lake Marion, the Santee, Cooper and Savannah rivers, and the ACE Basin. In the latter, shortnose sturgeon are typically found at the freshwater-saltwater interface. Adult and sub-adult shortnose sturgeon are known to inhabit this area during spring through fall. Spawning may take place well upriver; however, the existence of a spawning stock in the ACE Basin is yet to be determined.

Shortnose sturgeons are semi-anadromous; they migrate from the estuary into rivers to spawn. Adults migrate upstream in early spring and forage in the lower reaches of rivers at the fresh tidal water and estuarine water interface. This area is also an important nursery habitat for juveniles, which do not usually migrate. Migration of shortnose sturgeons and the extent to which they utilize freshwater habitats vary throughout the species' range. For instance, in northern latitudes, sturgeon make use of freshwater habitats more extensively than in southern regions, and some do not frequent estuarine habitats at all throughout the year. Sturgeons can live more than 50 years and typically grow very slowly. Growth and age at sexual maturity vary with latitude. Fish from southern locations grow faster and mature at a younger age than fish in the north. Male sturgeons inhabiting South Carolina waters become mature at approximately age 4 and females at age 6-7. Male sturgeons reproduce 1-2 years after reaching maturity. However, females may not spawn until 5 years after becoming mature. In South Carolina, the age at which female sturgeons first spawn ranges from 7 to 14 years. Spawning periodicity varies among individuals, but spawning rarely takes place in consecutive years. A female typically produces 27,000 to 208,000 eggs and can carry an egg mass of over 1 million eggs, depending on her body size. Spawning in South Carolina occurs from February to April over gravel or rubble bottoms. High current velocity and adequate substrate for the attachment of eggs are important factors in spawning site selection. Sturgeons are benthic feeders preferring mollusks and crustaceans as adults and insects and small crustaceans as juveniles.

A related species, the Atlantic sturgeon, is anadromous, spawning in freshwater rivers and spending the rest of its life in estuarine and nearshore waters. Females may spawn only every 2-6 years. Spawning in South Carolina begins in February and continues through the spring, with a second spawning migration possibly occurring in the fall. Spawning populations of Atlantic sturgeon in South Carolina are found in the Savannah River, one or more of the rivers in the ACE Basin, the Santee River, Winyah Bay and its river systems, and possibly the Cooper River. Although definitive spawning locations have not been identified, spawning is believed to occur in tidal freshwater, in deep areas with high water flow rates. A "marl hole" approximately 15 meters (50 ft) deep above Givhans Ferry on the Edisto River may be one of these locations. Females may release between 400,000 and 3.7 million eggs during a spawning period. As the eggs are released, they are fertilized externally by a male and then sink to the bottom. Sturgeon eggs are sticky and will adhere to rocks, plants, and other solid material. The eggs hatch within a week or so. Within three weeks, juvenile sturgeon have absorbed their yolk sac and begun to feed on bottom-dwelling organisms such as small shrimp, worms, clams, snails, and small demersal fish. Juvenile Atlantic sturgeon spend their first few years in rivers and estuaries with some movement along the coast. Tagging studies in South Carolina indicate that higher growth rates occur during the winter, spring and fall, with slower growth rates during the summer. As the juvenile sturgeon reach 0.6 to 0.9 meters (2-3 ft) in length (age of 1-6 years) , they begin to move into oceanic waters and join the adult population, remaining there until sexual maturity (7-19 years and nearly 2 meters or 6-7 ft in length). Atlantic sturgeon may undergo long migrations up and down the coast.

Species Significance

Worldwide, sturgeons are commercially valuable as a source of high-grade caviar, and their meat is popular both smoked and fresh. In the past, both Atlantic and shortnose sturgeons were reported in the landings for sturgeon. In the United States, Atlantic sturgeon supported a commercial fishery; however, landings have not exceeded 300,000 lbs. since 1920, and all Atlantic states have closed their fisheries in recent years. The sturgeon fishery was closed in South Carolina in 1985 following precipitous declines in numbers landed in the early 1980s. Shortnose sturgeons are currently of no commercial value because of their status as an endangered species. There is no recreational fishery for this species in the United States.

Shortnose sturgeon were listed as endangered throughout their range under the Endangered Species Conservation Act of 1969. In 1967, the U. S. Fish and Wildlife Service cited pollution and overharvesting as primary factors for the decline in numbers of shortnose sturgeon. Other sources contributing to population declines include incidental catch in shad gillnet fisheries, dam and bridge construction, dredging, entrapment in power plant water intake screens, and reservoir operations. In South Carolina, the primary factors affecting populations of this species are habitat alteration, due to dredging and dam construction, and pollution. Construction of dams has the potential to reduce suitable spawning sites, and disturbance associated with dredging activities impacts the food supply for juvenile sturgeon.

References

Collins, M.R. and T.I.J. Smith. 1993. Characteristics of the adult segment of the Savannah River population of shortnose sturgeon. Proceedings of the Annual Conference of the Southeastern Association of Fish and Wildlife Agencies 47:485-491.

Dadswell, M.J., B.D. Taubert, T.S. Squires, D. Marchette, and J. Buckley. 1984. Synopsis of biological data on shortnose sturgeon, Acipenser brevirostrum. Technical Report 14. National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Seattle, WA.

Hall, J.W., T.I.J. Smith, S.D. Lamprecht. 1991. Movements and habitats of shortnose sturgeon, Acipenser brevirostrum, in the Savannah river. Copeia 1991(3):695-702.

Leland, J.G., III. 1968. A survey of the sturgeon fishery of South Carolina. Bears Bluff Laboratory Contribution No. 47. Bears Bluff Laboratory, Wadmalaw, SC.

Murphy, S. H. and G. Barnette (eds.). South Carolina's endangered species portfolio. South Carolina Department of Natural Resources, Wildlife Diversity Section, Columbia, SC.

Shortnose sturgeon recovery team. 1997. Recovery plan for the shortnose sturgeon-public review draft. Office of Protected Resources, National Marine Fisheries Service. National Oceanic and Atmospheric Administration, Silver Spring, MD.

Taub, S.H. 1990. Fishery management plan for Atlantic sturgeon. Fisheries Management Report 17. Atlantic States Marine Fisheries Commission, Washington, DC.


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