Pallid Sturgeon

Scaphirhynchus albus

Description

The pallid sturgeon is a large, slow-maturing, long-lived freshwater fish. It has a flattened, shovel-like head, five rows of bony plates, and an unequally lobed tail. There is a row of sensory barbels in front of its ventral, toothless mouth.

This sturgeon is distinguished from the more common shovelnose sturgeon (Scaphirhynchus platorhynchus) by a number of characteristics. The pallid is lighter in color and attains a larger size. It appears smoother overall and has a longer nose. The most notable difference is the length and placement of the barbels. The pallid sturgeon's barbels are situated about a third of the distance from the mouth to the nose; those of the shovelnose sturgeon are at the midpoint between the two. The inner barbels of the pallid sturgeon are about half the length of the outer barbels; all the shovelnose sturgeon's barbels are about the same length. The species has also been known as Parascaphirhynchus albus, and by the common name of white sturgeon.

Behavior

Like other sturgeon species, the pallid is an opportunistic bottom feeder, consuming mollusks, crustaceans, worms, aquatic insects, and other fish. The barbels are sensory organs, and are important in the fish's feeding process.

The reproductive cycle of this sturgeon is not well known, although it is probably similar to other North American sturgeon species. Fish reach sexual maturity at about five years of age and spawn every few years thereafter. When spawning, small batches of sticky eggs are periodically released over a period of about 12 hours.

Habitat

The pallid sturgeon is found in large, turbid, free-flowing rivers with rocky or sandy bottoms. It inhabits swifter flowing waters than the related shovelnose sturgeon.

Distribution

The pallid sturgeon has been reported from the mouth of the Mississippi River to the mouth of the Missouri River; from the Missouri River as far as Fort Benton, Montana; and from the lower reaches of the Yellowstone River. The total length of the species' historic range was over 3,500 mi (5,600 km) and involved river habitat in 13 states: Louisiana, Mississippi, Arkansas, Tennessee, Kentucky, Missouri, Illinois, Iowa, Kansas, Nebraska, South Dakota, North Dakota, and Montana. While it appears that the pallid sturgeon was never abundant, it was once considered fairly common. As late as 1967, researchers were able to capture several fish in a single net set, and fishermen reported taking hundreds of pallid sturgeon as the reservoirs on the Missouri River filled.

The species still occurs in dramatically reduced numbers throughout much of its historic range. This decline is graphically illustrated by the number of pallid sturgeon sightings over the last three decades. In the 1960s, about 500 observations were made; in the 1970s, there were 209 sightings. In the 1980s, the number of observations fell to 65. The decline has been especially notable from the impounded sections of the Missouri River above the Gavins Point Dam along the South Dakota/Nebraska border.

Remnant populations probably exist in the Missouri River near the mouth of the Yellowstone River below Fort Peck, Montana; in the upper end of Lake Sharpe near Pierre, South Dakota, and between the mouth of the Platte River in Nebraska and Gavins Point Dam. Scattered sightings in the Mississippi River in the 1980s indicate that a small number of pallids may survive there.

Threats

The decline in pallid sturgeon populations has been caused by the alteration of virtually its entire river habitat by channelization and impoundment. About 51% has been channelized, 28% impounded, and the remaining 21% affected by the upstream impoundments.

The Mississippi and Missouri rivers have had an important role in the development of the nation's commerce, and since the early 1800s, they have been modified for commercial navigation. In the 1950s and 1960s, a series of dams were constructed on the Missouri River in North and South Dakota, in effect, turning the free-flowing river into a series of long narrow impoundments. This has led to a number of habitat changes which have apparently interfered with pallid sturgeon reproduction. Studies of the fish populations of the impoundments have consistently failed to document any young pallid sturgeon. There has been no documented reproduction in a decade, and the aging remnant population seems headed for extinction.

The dams block the normal movement of the sturgeon to historic spawning or feeding areas and have destroyed some spawning and nursery areas. They have produced changes to the water quality, temperature, and flow rates, which may affect reproduction and food sources.

Conservation and Recovery

Studies are underway, using the short-nose sturgeon as a surrogate species, to determine the feasibility of propagating the pallid sturgeon in captivity. During recent years, researchers have been developing new techniques to locate and caputure pallid sturgeon in preparation for a captive propagation program.

Since the federal government is heavily involved with the river habitats of the pallid sturgeon, agencies involved in dam operations and river channel maintenance will be consulting with the Fish and Wildlife Service on recovery of the species.

Natural reproduction has failed for at least one generation throughout the pallid sturgeon's range. Artificial propagation is being used to supplement wild populations until suitable spawning conditions in the wild can be restored. About 7,000 hatch-ery-reared pallids were released into the Mississippi River in 1994. To avoid potential hazards associated with inbreeding, domestication, and exposure to disease, extreme care is being taken in handling cultured stocks.

Attempts to spawn pallids taken from the Missouri and Yellowstone rivers in Montana have not been successful to date. When young are produced, the plan is to release them above Fort Peck Reservoir in a portion of the Missouri where 27 pallids have been recorded since 1990. The pallid sturgeon population in the Missouri River above Fort Peck is estimated at less than 100.

In the Missouri River, below Fort Peck Dam downstream to Lake Sakakawea (including the Yellowstone River below the mouth of the Powder River), 150 pallids have been handled since 1990 (this number includes 40 recaptures). The population estimate for these river stretches is 250 pallids.

Contacts

U.S. Fish and Wildlife Service
Division of Endangered Species
Denver Federal Center
P.O. Box 25486
Denver, Colorado 80225
http://www.r6.fws.gov/

U.S. Fish and Wildlife Service
Division of Endangered Species
Federal Building
Ft. Snelling
Twin Cities, Minnesota 55111
http://www.midwest.fws.gov/

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

References

Carlson, D. M., et al. 1985. "Distribution, Biology, and Hybridization of Scaphirhynchus albus and S. platorynchus in the Missouri and Mississippi Rivers." Environmental Biology of Fishes 14:51-59.

Deacon, J. E., G. Kobetich, J. D. Williams, and S.Contreras. 1979. "Fishes of North America, Endangered, Threatened, or of Special Concern." Fisheries 4(2):29-44.

Gilbraith, D. M., M. J. Schwalbach, and C. R. Berry.1988. "Preliminary Report on the Status of the Pallid Sturgeon, Scaphirhynchus albus, a Candidate Endangered Species." South Dakota State University, Brookings, South Dakota.

Hallemeyn, L. W. 1983. "Status of the Pallid Sturgeon (Scaphirhynchus albus )." Fisheries 8(1):3-9.

Hesse, L. W. 1987. "Taming the Wild Missouri River: What Has It Cost?" Fisheries 12(2):2-9.

Keenlyne, K. D. 1989. "A Report on the Pallid Sturgeon." U.S. Fish and Wildlife Service, Pierre, South Dakota.

Whitley, J. R., and R. S. Campbell. 1974. "Some Aspects of Water Quality and Biology of the Missouri River" Transactions of the Missouri Academy of Science 7-8:60-670.