The Borax Lake chub was emergency-listed as endangered in 1980, and a final listing rule with critical habitat (47 FR 43957) was published in 1982. A recovery plan was published in 1987.

Historical Status and Current Trends

The Borax Lake chub is endemic to Borax Lake and adjacent wetlands in the Alvord Basin, Harney County, Oregon. Population estimates of the chub in Borax Lake ranged from 10,625 to 34,634 during 1991 to 1997. Lower Borax Lake, which contained several thousand chubs during wet years in the mid-1980s was dry from 1989 to 1991 and currently has no fish.

Description and Life History

The Borax Lake chub is a dwarf species of the genus Gila (a widespread desert minnow). Adults are typically 33 to 50 millimeters (1.3 to 2 inches) standard length, with a maximum recorded size of 93 millimeters (3.6 inches) standard length. The Borax Lake chub has a large head which is concave in profile. The eyes are large, and the lateral line is reduced. Pharyngeal teeth are uniserial and well-hooked. Spawning can occur year-round, but primarily takes place in the fall and spring (Williams & Bond 1983, Scoppettone et al. 1995). Spawning occurs primarily in gravel, rock outcrop, and sand habitats, which comprise only 16 percent of the substrate of Borax Lake (Perkins et al. 1996). The Borax Lake chub is an opportunistic omnivore (Williams & Williams 1980, Scoppettone et al. 1995).

Habitat

Borax Lake, with its highly variable thermal springs, comprises one of the most unusual fish habitats in the United States. Borax Lake is a natural lake fed from the waters of several thermal springs, and is perched atop large sodium-borate deposits in the Alvord Desert. It is small and shallow, about 4.1 hectares (10 acres) in size. Spring inputs near the bottom of a deep vent, 32 meters (100 feet) below the surface, range from 40 to 148°C (104 to 300°F). Surface water temperatures typically range from 16 to 38°C (61 to 100°F) but fluctuations occur and temperatures occasionally exceed 38°C (100°F), causing fish kills as water temperature exceeds the chub's critical thermal maximum (Scoppettone et al. 1995). Water flows from Borax Lake into surrounding marshes, small pools, and Lower Borax Lake.

Reasons for Decline

The thermal waters feeding Borax Lake face a long-term threat from geothermal energy development. Proposals to drill wells near the lake prompted an emergency listing of this species as endangered in 1980. Other threats include modification of the fragile lake shorelines, which easily diverts water away from the lake, and overgrazing by livestock. The fragile salt-crust shoreline of the lake also is easily damaged by off-road vehicle use. The area is currently fenced to exclude livestock.

Conservation Measures

Protection afforded by the Endangered Species Act has greatly curtailed exploratory drilling for geothermal energy development by creation of a zone of no surface disturbance around the most sensitive habitats. The Nature Conservancy, a private conservation organization, purchased a 65-hectare (160 acres) parcel of private land including Borax Lake in 1993. An area of 260 hectares (640 ac) has been designated as critical habitat by the U.S. Fish and Wildlife Service, which affords additional protection from actions by federal agencies. The Steens Mountain Cooperative Management and Protection Act of 2000 (Public Law 106-399) has withdrawn geothermal and mineral development rights from the Borax Lake area. Additional conservation actions needed include: 1) closure of the critical habitat area to vehicle entry, 2) restoration of Lower Borax Lake and adjacent marshes, and 3) monitoring of fish, invertebrate, and habitat characteristics.

References

Perkins, D.L., C. E. Mace, G.G. Scoppettone, & P.H. Rissler. 1996. Identification of spawning habitats used by endangered Borax Lake chub (Gila boraxobius). United States Geological Survey, Biological Resources Division, Reno Field Station.

Scoppettone, G.G., P.H. Rissler, B. Nielsen, & M. Grader. 1995. Life history and habitat use of Borax Lake chub (Gila boraxobius Williams and Bond) with some information on the Borax Lake ecosystem. National Biological Service. Northwest Biological Science Center, Reno Field Station.

U.S. Fish and Wildlife Service. 1987. Recovery plan for the Borax Lake chub, Gila boraxobius. U.S. Fish and Wildlife Service, Portland, Oregon. 61 pp.

Williams, J. E. & C. E. Bond. 1980. Gila boraxobius, a new species of cyprinid fish from southeastern Oregon with a comparison to G. alvordensis Hubbs and Miller. Proceedings of the Biological Society of Washington. 93:291-298.

Williams, J. E. & C. E. Bond. 1983. Status and life history notes on the native fishes of the Alvord Basin, Oregon and Nevada. Great Basin Naturalist. 43:409-420.

Williams, J. E. & C.D. Williams. 1980. Feeding ecology of Gila boraxobius (Osteichthyes: Cyprinidae) endemic to a thermal lake in southeastern Oregon. Great Basin Naturalist. 40:101-114.

Williams, J.E. 1995. Threatened fishes of the world: Gila boraxobius Williams and Bond, 1980 (Cyprinidae). Environmental Biology of Fishes 43: 294.