Borax Lake Chub
Borax Lake Chub
|Listed||October 5, 1982|
|Description||Dwarf chub with an olive green back and silvery sides and black flecking.|
|Habitat||Mineralized lake fed by thermal springs.|
|Food||Diatoms, aquatic invertebrates, terrestrial insects.|
|Reproduction||Spawns year round.|
|Threats||Water diversion, geothermal exploration.|
The Borax Lake chub, Gila boraxobius, is a dwarf chub, ranging from 1.3-2.4 in (3.3-6 cm) in length. It has an olive green back with a dark mid-line, and silvery sides with black flecking, and a purplish iridescence. The eyes are large and protuberant. The jaw is elongated.
This chub is an opportunistic omnivore, feeding on diatoms, tiny crustaceans, insects and larvae, and detritus. It spawns throughout the year with peaks in spring and fall. Young are prominent in the shallow coves around the lake margin in May and June. Individuals live from one to three years.
Borax Lake is a 10.2-acre (4.1-hectare), highly mineralized natural lake, characterized by shallow waters (3.3 ft; 1 m), sparse aquatic vegetation, and a constant inflow from thermal springs. Outflow from the lake maintains a small pond and, in the past, extensive marshes between the lake and the pond. Over time, precipitation of salts from the spring water has raised the perimeter of the lake approximately 30 ft (9 m) above the valley floor, isolating the chub from the surrounding watershed.
From 1898 to 1907 the extensive salt deposits of the area were mined for borax. The lake is the site of the original Twenty Mule Team Borax Works, which shipped borax in wagons hauled by 20-mule teams to the railroad at Winnemucca, Nevada.
It is thought that this species evolved within the last 10,000 years in Harney County, Oregon. Al-ford Lake, a large pluvial lake, once covered this area. About 10,000 years ago the lake began to dry, and native fishes were restricted to remaining springs, lakes, and creeks. An ancestral stock became isolated in the springs of Borax Lake and adapted to the extreme conditions of the habitat, evolving into the form now recognized as the Borax Lake chub.
The Borax Lake chub is found only in Borax Lake, its outflow, and Lower Borax Lake, situated in the Alvord Basin of south-central Oregon (Harney County). Population estimates for Borax Lake made in 1986 and 1987 ranged between 6,000 and 14,000. There are thought to be an additional 8,000-10,000 chubs in Lower Borax Lake. The Borax Lake chub apparently experiences large swings in population caused by hot weather die-offs. Renewed spawning activity in the fall signals a rebound to pre-summer levels.
Borax Lake is a fragile aquatic ecosystem, which is particularly sensitive to alteration. In 1980 a modification of the lake perimeter to divert water lowered the water level by about 1 ft (0.3 m). This decreased the total area of chub habitat and increased the average water temperature of the lake. Much of the adjacent marsh dried up as a result of this diversion. Marshes around the lower lake retain water from permanent seepage.
The entire Alvord Basin is geothermally active, and the Bureau of Land Management (BLM) has leased geothermal exploration rights to private companies. Biologists fear that exploratory drilling in the area will disrupt interconnecting channels within the aquifer, lower water pressure, and cause the lake, which is above the valley floor, to go dry.
Conservation and Recovery
Within an area defined as habitat critical to the survival of the Borax Lake chub, the BLM owns 320 acres (130 hectares). Another 320 acres (130 hecatres) is privately owned, including the lake itself. In 1983 the Nature Conservancy secured a 10-year lease to the lake and—with the assistance of the Oregon Department of Fish and Wildlife and the BLM—has undertaken a program to rehabilitate the marshes by returning lake outflows to previous levels.
Regional Office of Endangered Species
U.S. Fish and Wildlife Service
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232
Ono, R. D., J. Williams, and A. Wagner. 1983. Vanishing Fishes of North America. Stonewall Press, Washington, D.C.
Williams, J. E., and C. E. Bond. 1980. "Gila boraxobius, a New Species of Cyprinid Fish from Southeastern Oregon with a Comparison to Gila alvordensis Hubbs and Miller." Proceedings of the Biological Society of Washington 92(2):291-298.
U.S. Fish and Wildlife Service. 1987. "Recovery Plan for the Borax Lake Chub, Gila boraxobius. " U.S. Fish and Wildlife Service, Portland.