Shortnose Sturgeon

Acipenser brevirostrum

Description

The shortnose sturgeon, Acipenser brevirostrum, is often confused with a young Atlantic sturgeon (Acipenser oxyrhynchus ), but it differs by having a wider mouth and shorter snout. Its underhanging mouth is preceded by four barbels, which function as sensory organs similar to the "whiskers" of a cat-fish. The yellowish brown body of the shortnose sturgeon is contrasted by its dark head and back. The undersurface is light yellow or white. The skeleton is largely cartilaginous, and scales are bony plates. Its maximum size is about 3 ft (90 cm), which is considerably smaller than a full-grown Atlantic sturgeon.

Behavior

Primarily nocturnal, the shortnose sturgeon feeds on crustaceans, insects, and small mollusks. It also ingests quantities of sediment, plant matter, and detritus. It is extremely long-lived, particularly in northern waters, sometimes reaching 50 years old.

It is a bay or estuary fish for most of its life but returns to freshwater streams and rivers to spawn. Very few individuals have ever been caught in the open ocean. Peak spawning occurs between February and May but may begin as early as January in the south. Females probably spawn only once every three years, depositing as many as 200,000 eggs, most of which do not survive. Juveniles mature in three to six years.

Habitat

The shortnose sturgeon prefers deep pools with soft substrates and vegetated bottoms, and moves from shallow to deeper water in winter. It spawns in freshwater wetlands or stream areas with fast flow and a gravel-cobble bottom.

Distribution

This shortnose sturgeon is found along the Atlantic coast from the St. John River in Canada to the Indian River, Florida. It was common in the Hudson, Delaware, Potomac, Connecticut, and St. Johns rivers.

The largest concentrations of the shortnose sturgeon are found in the St. John River (New Brunswick), Kennebec River (Maine), Hudson River (New York), Delaware River (New Jersey), Winyah Bay, Pee Dee River, and Lake Marion (South Carolina), and the Altamaha River (Georgia). In the last decade, a population was discovered in the Cape Fear drainage in North Carolina.

The most reliable population estimate for short-nose sturgeon in the Androscoggin and Kennebec Rivers DPS is the composite Schnabel estimate: An average of 7,222 with a 95% confidence interval of 5,046-10,765. This is considered to reflect a combined population of adult shortnose sturgeon that spawn throughout the Androscoggin/Kennebec Rivers DPS. Shortnose sturgeon are known to spawn in cycles, and estimates indicate that adults may spawn at intervals of three years.

In the Hudson River, a recent Cornell University study (1995-1997) sponsored by the National Marine Fisheries Service and the U. S. Army Corps of Engineers, used gill nets in high concentration areas of adult shortnose sturgeon and over large regions of the river to study the population numbers. The study, ongoing at the time of this publication, had so far tagged over 2,700 shortnose sturgeon; as part of the program, some 4,200 fish had been captured and measured since 1993. Using the 1995 data, researchers computed a preliminary mark-and-re-capture estimate of 55,265 adults (with a standard error margin of 10,436), seeming proof of a solid population growth over a 1992 estimate of 13,000.

Threats

In this century both the range and population size of the shortnose sturgeon have decreased. Part of this decline was caused by the countless dams that have been built along the Atlantic Coast, which cut off the sturgeon from many of its upriver spawning grounds. Water pollution has also been a significant factor in the decline of this species in the major rivers and estuaries. Late maturation, slow growth, and periodic spawning make it difficult for the sturgeon to replenish its numbers.

When originally listed, shortnose sturgeon were considered endangered throughout their range in the eastern United States, though not all extant populations were identified at the time of their original listing. Today, at least 17 populations of short-nose sturgeon are known within the species' wide latitudinal range. Recognizing that the knowledge concerning shortnose sturgeon increased during the years following the species' Endangered Species Act (ESA) listing, the National Marine Fish-eries Service (NMFS) began a status review in the late 1980s to assess whether individual shortnose sturgeon populations should be considered "distinct" for ESA purposes. In 1987, the NMFS announced a decision to combine the Androscoggin and Kennebec River populations as a single distinct unit, for ESA purposes

Although it is occasionally taken by sport fishermen who do not recognize it as distinct from the Atlantic sturgeon, the shortnose sturgeon is thought to be adequately protected by existing game fish regulations. It is unlawful under provisions of the Endangered Species Act to possess (alive or dead) or harass a shortnose sturgeon.

Conservation and Recovery

The NMFS' 1996 "Status Review of Shortnose Sturgeon in the Androscoggin and Kennebec Rivers" analyzed listing factors from the ESA and concluded that the sturgeon continued to be endangered due to substantial habitat and/or range threats resulting from hydroelectric facilities, channel dredging, and the introduction of pollutants via sewage treatment plants, paper mills, and other industrial facilities. It found, however, that overutilization of the fish for commercial, recreational, scientific, or commercial purposes was not a threat at the time, although pressure for commercial utilization could increase if the species were removed from protected status. It also found that existing regulatory mechanisms other than the ESA may limit the direct harvest of shortnose sturgeon but are inadequate to ensure the detailed review of potentially damaging construction activities closely scrutinized through the ESA Section 7 consultation process.

Documented recovery criteria for shortnose sturgeon populations do not currently exist, although the NMFS Shortnose Sturgeon Recovery Team, established in 1992, is presently drafting a "Shortnose Sturgeon Recovery Plan" that will include such criteria. Factors in developing the plan include the outcome of research to determine the extent of the spawning areas and to expand basic knowledge of the sturgeon's biology.

Contacts

U.S. Fish and Wildlife Service
Division of Endangered Species
1875 Century Blvd., Ste 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

U.S. Fish and Wildlife Service
Division of Endangered Species
300 Westgate Center Dr
Hadley, Massachusetts 01035
http://northeast.fws.gov/

References

Dadswell, M. J., et al. 1984. "Synopsis of Biological Data on Shortnose Sturgeon, Acipenser brevirostrum." Report NMFS 14, National Marine Fisheries Service, Washington, D. C.Ross, S. W., et al. 1988. Endangered, Threatened, and

Rare Fauna of North Carolina: A Re-evaluation of the Marine and Estuarine Fishes. Occasional Papers of the North Carolina Biological Survey, Raleigh.

U.S. Fish and Wildlife Service. 1982. "Recovery Plan for the Shortnose Sturgeon." U.S. Fish and Wildlife Service, Hadley, MA.

Vladykov, V. D., and J. R. Greeley. 1963. "Order Acipenseroidei in Fishes of the Western North Atlantic." Memoir Sears Foundation for Marine Research 1(3), 1963:24-60.