GULF STURGEON

(Acipenser oxyrhynchus desotoi)

FAMILY: Acipenseridae

STATUS: Threatened, Federal Register, September 30, 1991

DESCRIPTION AND REPRODUCTION: The Gulf sturgeon, also known as the Gulf of Mexico sturgeon, is a subspecies of the Atlantic sturgeon. It is an anadromous fish with a sub-cylindrical body imbedded with bony plates or scutes. The snout is greatly extended and bladelike with four fleshy chin barbels in front of the mouth which is protractile on the lower surface of the head. The upper lobe of the tail is longer than the lower lobe. Body color is light brown to dark brown and pale underneath. The species grows to a maximum length of about 8 feet and is over 200 pounds in weight.

BIOLOGICAL INFORMATION: Populations in the Suwannee River and Apalachicola River have been fairly well studied over the past decade using ultrasonic and radio telemetry and conventional sampling gear. Subadult and adult fish begin migration into rivers from the Gulf of Mexico in early spring and continuing until early May (Carr 1983, Wooley and Crateau 1985, Odenkirk 1989, Clugston et al. in press). In late September or October, subadult or adult sturgeon begin downstream migrations. Sturgeon apparently only feed during their stay in marine waters; food items are rarely found in the stomachs of specimens sampled from rivers. In the vicinity of the Suwannee River, the primary foods of juveniles are amphipods with isopods, annelids, dipterans, blue crab parts, lancelets, brachipods, and plant material (Huff 1975, Mason and Clugston 1993). Gulf sturgeon are long-lived, reaching an age of at least 28 years. Not surprisingly, the fish gain weight during their tenure in marine waters and subsequently lose weight during their stay in fresh water. Growth of fish aged 2 to 5 appears rapid (9.4 inches a year), but decreases to 3.1 inches a year between ages 6 to 8 (L.G. Jenkins, unpublished manuscript). Spawning of Gulf sturgeon is not well documented. However, a few larval sturgeon have been collected in early April and early May in the Apalachicola River (Wooley et al. 1982). Observations of ultrasonic tagged gravid females by S. Carr suggests that spawning takes place in the immediate vicinity of springs with primarily rocky substrates. Age at sexual maturity for females ranges from 8 to 17 years, and for males from 7 to 21 years (Huff 1975). Fecundity in Gulf sturgeon, based on three individuals, ranged from 274,680 to 475,000 eggs per female, or an average of 20,652 eggs a pound (Chapman et al. 1993).

RANGE AND POPULATION LEVEL: The Gulf sturgeon is restricted to the Gulf of Mexico and its drainages, primarily from the Mississippi River to the Suwannee River, in Louisiana, Mississippi, Alabama, and Florida. The subspecies may also occur sporadically as far west as Texas, and in marine waters in Florida south to Florida Bay. Historic data indicate that populations have declined. Current population estimates are known only for the Apalachicola River and Suwannee River. The U.S. Fish and Wildlife Service has monitored the Apalachicola River population since 1979. Since 1984, the population size in this river has ranged from 96 to 131 fish, with a mean of 115 (USFWS 1990). In the Suwannee River, which appears to support the most viable population of the Gulf sturgeon, a 1986 mark and recapture study estimates the annual population of between 2,250 to 3,000 fish, averaging about 40 pounds in size (S. Carr, Caribbean Conservation Corporation, personal communication). Commercial landing records show that the only consistent fisheries for Gulf sturgeon occurred in West Florida, especially in the Apalachicola River, from around 1900 to the 1970's.

HABITAT: This fish is anadromous; immature and mature individuals participate in fresh water migrations. Adult fish spend 8 to 9 months each year in rivers and 3 to 4 of the coolest months in estuarine or Gulf waters. Young fish under 2 years of age apparently do not migrate out of rivers and estuaries. In the Suwannee River, adult sturgeon frequent areas near the mouths of springs and cool-water rivers during the summer months. Adult fish tend to congregate in deeper waters of rivers with moderate currents and sand and rocky bottoms. Seagrass beds with mud and sand substrates appear to be important marine habitats (Mason and Clugston 1993).

REASONS FOR CURRENT STATUS: Habitat destruction and degradation, exacerbated by potential over-exploitation of the species, are primarily responsible for the sturgeon's decline. Dams have prevented access to historic sturgeon migration routes and spawning areas (Wooley and Crateau 1985). Dredging and other navigation maintenance, possibly including lowering of river elevations and elimination of deep holes and altered rock substrates, may have adversely affected Gulf sturgeon habitats (Wooley and Crateau 1985). A decrease in groundwater flows has reduced cool water habitats, which are thought to be warm water refugia for sturgeon (S. Carr, personal communication); recent droughts in the Apalachicola River system have aggravated the loss of cool water refugia. Increased groundwater withdrawal for irrigation in southwest Georgia may result in a 30 percent reduction of discharge to streams (Hayes et al. 1983). Contaminants, both agricultural and industrial, may also be a factor in their decline. Organochlorines have been documented in Gulf sturgeon at levels that may cause reproductive failure, reduced survival of young, or physiological alterations in other fish (White et al. 1983). To compound these anthropogenic impacts, the life history of the Gulf sturgeon complicates recovery efforts. Breeding populations take years to establish because of their advanced age at sexual maturity. In addition, Gulf sturgeon appear to be homestream spawners with little, if any, natural repopulation from migrants from other rivers.

MANAGEMENT AND PROTECTION: The concerted efforts of numerous public and private organizations has resulted in a fairly substantial body of information necessary for the management and protection of the Gulf sturgeon. Commercial harvest of this species has been eliminated by Louisiana, Mississippi, Alabama, and Florida. Gulf sturgeon have been experimentally reared for life history studies and possible reintroduction into the wild. Primary recovery goals are to prevent further reductions in existing wild populations, establish population levels that would allow delisting of the species by river systems, and to establish, following delisting, self-sustaining populations that could withstand directed fishing pressure within each river system. Other goals are to continue to characterize, protect, and restore essential habitats, evaluate population levels rangewide, refine life history studies, and reduce or eliminate incidental mortality.