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Shortnose sturgeon |
The shortnose sturgeon (Acipenser brevirostrum) formerly occupied rivers and estuaries along the Atlantic seaboard from New Brunswick to northern Florida [1]. It was driven to near extinction by overfishing, by-catch in the shad fishery, damming of rivers, habitat destruction, and deterioration of water quality. Scientists and fishermen in the 19th and early 20th centuries did not distinguish between Atlantic and shortnose sturgeon, so there are no historical population estimates. Clearly, however, by the early 20th century populations were declining and by the 1950s or earlier had become endangered. The sturgeon was placed on the endangered species list of 1967.
Shortnose sturgeon populations are divided into 19 management units based on presumed reproductive isolation [1]. Recent genetic analysis generally supports the management units, but suggests that the Delaware River be combined with Chesapeake Bay and the Ogeechee River be combined with the Altamaha River [2]. The 1987 draft and 1988 final federal recovery plans recommended that each of the units be treated as a distinct population segment that can be recovered and delisted separately. The 1987 draft recommended downlisting the Connecticut, Delaware, and Hudson River populations to "threatened" and delisting the Kennebec System population as recovered. - Seven large populations (>=1,000 fish): Saint John River (NB), Kennebec System (ME), Connecticut River (CT, MA), Hudson River (NY), Delaware River (DE, NJ, PA), Savannah River (SC), and Altamaha River (GA). - Five improved populations: Kennebec System (ME), Connecticut River (CT, MA), Hudson River (NY), Savannah River (SC), and Altamaha River (GA). Five of the seven large populations, and four of the six improved/stable population are north of Chesapeake Bay. The southern populations are generally smaller and less well known. Six of the seven large populations are improved/stable. All of the unknown populations are small/very small with the exception of the St. John River (NB). The latter trend likely indicates that the small populations consist of numbers too small support robust trend estimates. The species overall trend has improved since being placed on the endangered species list in 1967. IMPROVING POPULATIONS * Connecticut River (CT, MA): Sturgeon in the upper and lower Connecticut River have been largely separated by the Holyoke Dam for 157 years. The Upper Connecticut River was estimated to support 297-515 total fish 1976-1978 and 47 and 98 spawning fish in 1992 and 1993 respectively [1]. The Lower Connecticut supported approximately 875 adults in 1988-1993 [1, 8] and 1,800 in 2003 [8]. * Hudson River (NY). The shortnose sturgeon occupies a 246-km section of the Hudson River from New York City to Troy Dam upstream of Albany [4]. This population is larger than the other 19 management populations combined. From late spring through early fall adults use deep, channel habitats of the freshwater and brackish reaches of the estuary. In the late fall, most or all adults concentrate at a single overwintering site in the river channel near Kingston while juveniles remain in the estuary. In the spring, adults spawn at a single location slightly downstream of the Troy Dam. The larvae gradually disperse downstream with juvenile sturgeon that inhabit much of the estuary during the summer, but occupy a more limited range in the southern portion of the estuary during winter. Due to fishing prohibitions and habitat protection efforts (the population has not been augmented with hatchery fish or translocations), numbers in the Hudson River increased dramatically between 1979 (12,669 spawning fish (95% CI = 9,080-17,735)), 1980 (13,844 (95% CI = 10,014-19,224)), and 1994-1996 (56,708 (95% CI = 50,862-64,072)) [4]. The size and age of individual fish and the demographic structure of the population as a whole indicate a healthy condition typical of non-endangered, long-lived species. * Savannah River (SC): Between 1984 and 1992, approximately 97,000 shortnose sturgeon were stocked in the Savannah River [1]. The 1999-2000 population had many more adults than in 1992, primarily due to presence of stocked fish, but there was little evidence of reproduction [3]. The 1999 population was estimated at 3,000 fish [5]. * Altamaha River (GA): Population estimates on the Altamaha River were 2,862 total fish in 1988 (95% CI=1,069-4,226) [1], 798 in 1990 (95% CI=645-1,045) [1], 468 in 1993 (95% CI=316-903) [1], and 5,910 (95% C.I. 4,740-7,848) in 2003-2005 [7]. STABLE POPULATIONS UNKNOWN POPULATIONS * Merrimack River (MA): unknown trend. The 1989-1990 population was estimated at 33 total fish [1]. * Penobscot (ME) Dennys, Machias, East Machias, Ducktrap: the last report is of a single fish in 1978 [2]. * Chesapeake Bay (MD, VA): unknown trend, very small population [1, 5]. * Winyah Bay (Waccama, Pee Dee, Black Rivers; SC, NC): unknown trend [1]. * Cape Fear River (NC): unknown trend, likely less than 50 individuals [1, 5]. * Santee River (SC): unknown trend [1]. * Cooper River (SC): unknown trend [1], 100-300 fish in recent years [5]. * "ACE" Basin (Ashepoo, Combahee, and Edisto Rivers; SC): unknown trend [1]. * Satilla River (GA): unknown trend * Ogeechee River (GA): unknown trend. The 1993 population was estimated to have 266 adults [9] and 361 total fish [1]. The 1999 population was estimated at 195 adults, which was not statistically different from the 1993 estimate [9]. * St. Marys River (FL): unknown trend. [1] National Marine Fisheries Service. 1998. Recovery Plan for the Shortnose Sturgeon (Acipenser brevirostrum). Silver Springs, Maryland. 104 pages. |
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