Andrew M. Lazur
University of Maryland Center for Environmental Sciences, Horn Point Laboratory
Two species of sturgeon are native to the Chesapeake Bay, the Atlantic, Acipenser oxyrhynchus, and shortnose, Acipenser brevirostrum, with natural ranges from Canada to Florida. Atlantic and shortnose sturgeon were of significant commercial importance being harvested primarily for their highly prized roe or caviar. In the late 1880's, sturgeon was an important cash crop with a peak harvest of about 7 million pounds of which approximately 10% was harvested from the Chesapeake Bay. Commercial catch declined rapidly after the turn of the century with annual harvests from 1905 to the 1990's amounting to less than 5% of the record catch.
Present Status of Populations
Due to decline in sturgeon populations resulting from over fishing, dam construction, deforestation, and habitat destruction. Historical records of Atlantic sturgeon landings. Throughout the Atlantic coast, shortnose sturgeon was listed as an endangered species by the US Fish and Wildlife Service in 1967. A moratorium on all US commercial harvest was established for Atlantic sturgeon in 1997. Current estimates for the Chesapeake Bay suggest that the shortnose population is extirpated or too low to sustain a viable population. Recently, increased fish numbers caught near the Susquehanna and Potomac rivers were determined to have migrated through the C&D canal from the Delaware River. The situation for Atlantics appears to be similar with no young of year fish being caught during surveys for the past 45 years. The unique life history of sturgeon contributed to its population decline as well as presenting challenges to its recovery.
Life History and Recovery Implications
Sturgeon are one of a few Jurassic fish species still in existence today with 26 sturgeon species distributed in cold to temperate climates of the northern hemisphere. In addition to the Atlantic and shortnose, 6 other sturgeon species are found in North America. The white sturgeon, found on the Pacific coast, stills exists in adequate numbers to support a recreational and guide fishing industry and is also being cultured on farms for meat and caviar. Like most sturgeon, Atlantic and shortnose are anadromous, living in salt or brackish waters and migrating into freshwater rivers to spawn. Given this reproductive requirement, it is easy to understand the negative impact that damming rivers has on sturgeon spawning and populations. Another reproductive characteristic of sturgeons which adds to the challenge of recovery is their relatively long period (5 to 30 years depending on species and location) to reach sexual maturity. In addition, sturgeon may only spawn once every 2-3 years. Most other fishes, including the likewise anadromous striped bass, begin to spawn at 3-4 years of age, and can spawn every year. Adult sturgeon begin migrating into freshwater rivers to spawn in late winter and early spring seeking a hard or pebbly/gravel bottom with water currents capable of preventing settling of sediments. Soil erosion, from human disturbances or weather events can significantly increase sediment loading and degrade sturgeon spawning grounds. Additionally, young and adult sturgeon are bottom feeders preferring small crustaceans, bivalves and worms. Excessive sediment accumulation, hypoxic conditions at bottoms caused by eutrophication and elevated nitrogenous compounds, can further impact sturgeon, especially fry and juveniles. To be effective restoration or recovery efforts must take these special characteristics and spawning habitat needs into account.
Despite the environmental challenges and unique biological requirements, sturgeon is a good candidate for stock enhancement or restoration. Without an existing fishery or an expectation for one, sturgeon populations, either naturally occurring or hatchery reared, would not be impacted by harvesting as is the case for other fisheries. The knowledge base for spawning and culturing sturgeon via aquaculture is significant with proven technology. Controlled conditions of hatchery culture offer the advantage of being able to significantly increase the survival of eggs and fry and to produce advanced fingerlings which could better survive current environmental conditions. Stocking larger fish could greatly supplement existing stocks and serve as a boost towards achieving a viable reproductive base in the next decade when improved water quality conditions will better support survival of fry and juveniles. This approach was investigated in 1996, when Maryland DNR conducted an experimental stock enhancement project by stocking 3,000 juvenile Atlantic sturgeon in the Nanticoke river on the Eastern Shore. A reward program was established and 14% of these fish were recaptured from stocking to 2001 indicating good survival. In addition to the capture of stocked fish, over 500 wild sub-adult Atlantic sturgeon were caught, but no wild juvenile fish. The results of the project further supports the notion that it is unlikely that Atlantic sturgeon are currently reproducing in Maryland, but that the potential for using hatchery-reared fish for restoration is promising.
Restoration Plans and Outlook
Successful recovery of sturgeon hinges on many factors collectively including spawning and nursery habitat restoration, pollution reduction and other water quality improvement, and potential reintroduction of stocks. Recovery and management plans have been developed for both species which integrate these and other factors. The Atlantic State Marine Fisheries Commission, a consortium of all 15 of the Atlantic coast states' fisheries resource management agencies, regulates Atlantic sturgeon and has developed a protocol for stock enhancement. The National Marine Fisheries Service (NMFS), is responsible for marine and anadromous species listed under the Endangered Species Act (ESA), and, therefore, regulates shortnose sturgeon. NMFS, through a specified recovery team, has also developed guidelines for restoration of shortnose in a comprehensive recovery plan. Both plans review current populations, habitat and water quality enhancement needs, but also address other important considerations of recovery such as concern over genetic diversity and long-term viability of stocks including potential hatchery supplementation. Through DNA analysis, it has been determined that fish from specific rivers or adjacent rivers have distinct genetic characteristics. In the ASMFC breeding and stocking protocol for cultured sturgeon, specific recommendations on broodstock sources and hatchery production programs are presented to address genetic diversity concerns. Among these recommendations are: 1) Using broodfish from the same river (preferred source) or adjacent river (if only source available) to be stocked; 2) populations that are determined to be extirpated should be given highest priority for stocking; 3) a pool of least 100 broodfish be used with a minimum of six year classes and stocking be continued (varies depending on year classes available, but could be 10 plus years); and 4) a maximum of 50,000 fingerlings per female per season be stocked and all fish be tagged or marked and monitored.
Sturgeon are an interesting and unique species of fish having played a major role in the historical fishing industry of the Chesapeake Bay. The decline in Bay sturgeon populations, caused by over-harvest, habitat and water quality degradation, has persisted for over a century resulting in sturgeon being the only resource species near extinction today. Recovery plans and protocols outlining the role of aquaculture hatcheries and results of the 1996 restocking study, provide sound guidance and encouragement that sturgeon stocks can be restored. Recovery involves a long-term commitment to an integrated approach of habitat and water quality improvements and development of adequate captive broodstock and hatchery resources. Investment in this effort can be beneficial to the entire ecosystem as well as assisting in the return of one of the Chesapeake Bays' signature species.
Suggested Information Sources
ASMFC Breeding and Stocking Protocol for Cultured Atlantic Sturgeon.
Final Recovery Plan for the Shortnose Sturgeon, NFMS.
Maryland DNR Hatcheries and Fisheries Restoration Program.
Secor, D.H. and E.J. Niklitschek. 2001. Hypoxia and sturgeons: report to the Chesapeake Bay Program dissolved oxygen criteria team. Technical Report Series No. TS-314-01-CBL; Chesapeake Biological Laboratory, Solomons, Maryland.
Secor, D.H., P.A. Anders, W. Van Winkle, and D.A. Dixon. 2002. Can we study sturgeon to extinction? What we know and don't know about the conservation of North American sturgeons. American Fisheries Society Symposium 28:3-10.