Virgin River Chub

Gila robusta seminuda

Description

The Virgin River chub (Gila robusta seminuda ) is a silvery fish in the minnow family that usually grows to about 8 in (20 cm) but has been known to attain a length of 18 in (45 cm). It has an elongated body with a narrow tail and deeply cleft caudal fin. It is distinguished from other subspecies of G. robusta by the number of rays in the dorsal, anal, and pelvic fins (9-10) and the number of gill rakers (24-31). It has small, embedded scales on its back, breast, and belly that are difficult to see, which accounts for the subspecific name seminuda.

Behavior

The Virgin River chub is omnivorous, feeding on algae, aquatic and terrestrial insects, crustaceans, and organic detritus. Little is known about its spawning behavior.

Habitat

This chub prefers deep, swift-flowing water, where there are boulders or other cover. It is tolerant of high salinity and turbidity and occurs over sand and gravel bottoms in water less than 86°F (30°C).

Distribution

It is believed that the Virgin River chub once inhabited about 134 mi (215 km) of the Virgin River, from its confluence with the Colorado River upstream to La Verkin Creek, near Hurricane, Utah. In the late nineteenth century it was considered common. Today, this subspecies is restricted to a 50-mi (80-km) portion of the Virgin River, between Mesquite, Nevada, and La Verkin Creek, near Hurricane, Utah. The land bordering this stretch of the river is both public and privately owned. In Arizona, the federal Bureau of Land Management (BLM) administers about 80-90% of the river frontage; privately owned land is concentrated in the vicinity of Littlefield. In Utah, about 13 mi (21 km) are managed by BLM; the state owns four small parcels and the rest is privately owned. In Nevada, land north of the town of Mesquite is in private hands.

Threats

The original range of the Virgin River chub was reduced almost 60% by nineteenth-century water diversions and the construction of Hoover Dam and Lake Mead. The chub is currently threatened by further water removal and impoundments, reduced reproduction, and competition from introduced fish species.

Although the Virgin River chub has survived a major reduction of its habitat caused by dams and water diversions, additional impoundments or diversions may drive the subspecies toward extinction. Federal listing as an Endangered species will require the Washington County Conservancy District (which has identified four potential reservoir sites) and the federal Soil Conservation Service (an agency of the Department of Agriculture which is planning flood control and irrigation projects) to make provisions for the conservation of the chub and its habitat.

The population of many river species often fluctuates because of changing environmental conditions, many of which are poorly known. However, it is clear that the species' survival is heavily dependent on the frequency of successful reproductive years. Recent studies have indicated that between 1984 and 1988, the Virgin River chub had only one good reproductive year.

Several other recent events have affected Virgin River chub populations. In 1988, an attempt was made to eradicate the exotic red shiner (Notropis lutrensis) from the Virgin River from the Washington Fields diversion downstream to the Virgin River Gorge. This introduced species is a major threat to native species. In 1985, it became established in the St. George area and within a year became the dominant fish species. After first salvaging 1,200 Virgin River chub, all remaining fish in that 21-mi (33-km) stretch of the river were eradicated and a barrier dam was installed at the head of the Virgin River Gorge to prevent return of the shiner.

Another 1988 event had a major impact on Virgin River fish populations. A dike at the Quail Creek Reservoir failed, releasing 25,000 acre-feet (30 billion l) of water into the river. This scouring flood is believed to have had a devastating effect on the entire fish population of the Virgin River.

Conservation and Recovery

In 1995, a Recovery Plan was released for the Virgin River chub in the Virgin River. Necessary actions identified in the recovery plan include habitat acquisition and protection, regulation of flows from the Quail Creek Reservoir System, and monitoring and research studies of the rare fish. Critical habitat of the Virgin River chub in the Virgin River was designated in 2000, an action that will focus recovery efforts for the rare fish. The recently discovered population of the Virgin River chub in the Muddy River is covered within the context of all rare aquatic species in the Recovery Plan for the Muddy River ecosystem, released in 1996. As part of the recovery process, a captive population of Virgin River chub is held at the Dexter National Fish Hatchery as insurance against extinction and as a source of fish for restocking efforts.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 1306
Albuquerque, New Mexico 87103-1306
Telephone: (505) 248-6911
Fax: (505) 248-6915
http://southwest.fws.gov/

U. S. Fish and Wildlife Service
145 East 1300 South, Suite 404
Salt Lake City, Utah 84115-6110
Telephone: (801) 524-5009
Fax: (801) 524-5021

References

Cross, J. N. 1975. "Ecological Distribution of the Fishes of the Virgin River (Utah, Arizona, Nevada)." Master's thesis. University of Nevada, Las Vegas.

Heckman, R. A., J. E. Deacon, and P. D. Gregor.1966. "Parasites of the Woundfin Minnow, Plagopterus argentissimus, and Other Endemic Fishes from the Virgin River, Utah." Great Basin Naturalist 46(4): 663-676.

Hickman, T. J. 1988. "Study of Fishes in the Virgin River (Utah)." Annual Report for 1987. Western Ecosystems, St. George, Utah.

Rinne, John N., and W. L. Minckley. 1991. Native Fishes and Arid Lands: Dwindling Resource of the Desert Southwest. USDA Forest Service, Fort Collins, Colorado.

U. S. Fish and Wildlife Service. 1995. "Virgin River Fishes Recovery Plan." U. S. Fish and Wildlife Service, Denver, Colorado.

U. S. Fish and Wildlife Service. 1996. "Recovery Plan for the Rare Aquatic Species of the Muddy River Ecosystem." U. S. Fish and Wildlife Service, Portland, Oregon.