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Borax Lake Chub
Borax Lake chub Gila boraxobius is represented by a
single population that inhabits a 4.1 hectare geothermally-heated
alkaline lake in Harney County, Oregon. This species was listed as
endangered under the federal Endangered Species Act in 1982. In 2005,
the Oregon Department of Fish and Wildlife's Native Fish Investigations
Project initiated a study to 1) monitor population abundance of Borax
Lake chub, 2) evaluate ways to reduce handling of Borax Lake chub when
monitoring population abundance both by modifying previous
mark-recapture protocols and by developing snorkeling survey protocols
to use as an alternative to mark-recapture estimates, 3) monitor habitat
conditions, and 4) develop a long-term monitoring strategy.
The Borax Lake chub is a small minnow endemic to Borax Lake and
adjacent wetlands in Oregon's Alvord Basin (Williams and Bond 1980).
Borax Lake is a natural lake, perched 10 meters above the desert floor
on sinter deposits, which is fed almost exclusively by thermal
groundwater.
Population abundance estimates
obtained in 1986-1996 indicated a fluctuating population ranging from 3,934 fish to 34,634 fish. The
basis for the Borax Lake chub's listed status was not population size,
but the security of a very limited, unique, isolated, and vulnerable
habitat. Aging data suggests that the Borax Lake chub population
consists primarily of age 1 fish, with few age 2 and older fish
present. Because Borax Lake chub are only found in one location and the
population is apparently dominated by a single year-class of adults, the
species has a high inherent risk of extinction.
Numerous recovery measures implemented since listing have improved the
conservation status of Borax Lake chub and protection of its habitat.
When the species was listed, critical habitat was designated on 259
hectares of land surrounding the lake, including 129 hectares of public
lands and two 65-hectare parcels of private land. In 1983, the U.S.
Bureau of Land Management designated the public land as an Area of
Critical Environmental Concern. The Nature Conservancy began leasing
the private lands in 1983 and purchased them in 1993, bringing the
entire critical habitat into public or conservation ownership. The
Nature Conservancy ended water diversion from the lake for irrigation
and livestock grazing within the critical habitat. Passage of the
Steens Mountain Cooperative Management and Protection Act of 2000
removed the public BLM lands from mineral and geothermal development
within a majority of the basin. These actions, combined with detailed
studies of the chub and their habitat have added substantially to our
knowledge of the Borax Lake ecosystem. However, three primary threats
remain. These include the threat to the fragile lake shoreline,
wetlands, and soils from a recent increase in recreational use around
the lake (particularly off-road vehicle usage), the threat of
introduction of nonnative species, and potential negative impacts to the
aquifer from geothermal groundwater withdrawal if groundwater pumping
were to occur on private lands outside the protected areas.
Annual Reports and Publications:
Scheerer, P. D. and S. E. Jacobs. 2007. 2007 Borax Lake Chub
Investigations. Oregon Department of Fish
and Wildlife, Fish Research Project E-2-41, USFWS contract
134206M085, and BLM contract HAP074439, Annual Progress Report,
Corvallis.
Scheerer, P. D. and S. E. Jacobs. 2006.
2006 Borax Lake Chub Investigations.
Oregon Department of Fish and Wildlife, Fish Research Projects E-2-40, E-2-40 Supplement, and
The Nature Conservancy, Annual Progress Report, Corvallis.
Scheerer, P.D. and S.E. Jacobs. 2005.
Borax
Lake Chub population assessment and monitoring strategy.
Oregon Department of Fish and Wildlife, Fish Research Project 134204M129
Annual Progress Report, Corvallis.
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