Owens Tui Chub
Owens Tui Chub
Gila bicolor snyderi
|Listed||August 5, 1985|
|Description||Olive and white chub with lateral blue and gold reflections.|
|Habitat||Streams, rivers, irrigation ditches.|
|Reproduction||Spawns when water temperature reaches 64°F (17.8°C).|
|Threats||Water diversion, competition from nonnative fishes, hybridization.|
The Owens tui chub, Gila bicolor snyderi, is a moderate to large subspecies of G. bicolor, with males reaching 4 in (10 cm) and females slightly more than 5 in (13 cm) in length. It is olive above and whitish below, with lateral blue and gold reflections. The side of the head is noticeably gold. Its mouth lining and tongue are purplish. It has a large head and eyes, and the greatest body depth is just behind the head. It has the heaviest, strongest pharyngeal teeth of any known G. bicolor species.
The Owens tui chub has been known since the late 1800s, but was not described as a new sub-species until 1973.
Little is known about this chub's reproductive characteristics, but it is thought that spawning occurs when water temperature reaches 64°F (17.8°C). Juveniles appear to use shallow margins as nursery areas.
Little is known about food requirements as well, but comparing the Owens tui chub with sympatric species, it is assumed that juveniles are insectivorous and adults are omnivorous.
Some periodicity has been recorded. It has been observed invading newly flooded shallows in the evening and returning to deeper water in the morning. It also appears that spawning fish migrate to more shallow areas in the spring and summer, and return to deeper water in the fall and winter.
Based on past collections, the Owens tui chub occupied various habitats ranging from thermal spring pools, supporting only a few hundred individuals, to the mainstream of the Owens River, where the population numbered in the tens or hundreds of thousands. Primary habitat requirements appear to be clear, clean water, adequate cover in the form of rocks, undercut banks, or aquatic vegetation, and sufficient insect food. Preferred habitat conditions seem to include streams with a slow current, mud bottoms, clear water, and submerged vegetation.
The Owens tui chub has been recorded in Owens Lake, Owens River, tributary streams, and irrigation ditches throughout the Owens River basin (Inyo and Mono Counties), California. Because of extensive hybridization throughout the basin, genetically pure populations of the Owens tui chub are now known from only two locations in Mono County—in the source springs of Hot Creek, and a 8-mi (13-km) stretch of the Owens River below Long Valley Dam. Both sites are within the Inyo National Forest but are owned by the city of Los Angeles. The present distribution represents less than 1% of its historic range.
Demand for water from the Owens River basin for irrigation and human consumption is high. The river has been dammed at several places and much of its water is diverted through aqueducts to Los Angeles, more than 260 mi (415 km) to the south. The resulting reduction of stream flow has degraded water quality and greatly restricted available habitat for this chub.
The surviving Owens tui chub populations are also threatened by predators, such as the introduced brown trout, and by interbreeding with the Lahontan tui chub (G. b. obesa ). This non-native chub was introduced illegally into the Owens River as a baitfish.
Conservation and Recovery
The California Department of Fish and Game, Bureau of Land Management, and the U. S. Fish and Wildlife Service (FWS) have repeatedly tried to reintroduce the Owens tui chub to Fish Slough in Mono County. To date, however, transplanted chubs have not survived. Further reintroduction efforts will be based on the results of ongoing research into the chub's habitat preferences.
In 1986 the FWS and the state Department of Fish and Game reached an agreement to maintain the chub's habitat at Hot Creek Springs.
Regional Office of Endangered Species
U.S. Fish and Wildlife Service
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232
Miller, R. R. 1973. "Two New Fishes, Gila bicolor snyderi and Catostomus fumeiventris, from the Owens River Basin, California." Occasional Papers of the Museum of Zoology, University of Michigan 667:1-19.
Pister, E. P. 1981. "The Conservation of Desert Fishes." In R. J. Naiman and D. L. Solts, eds.,Fishes in North American Deserts. John Wiley and Sons, New York.
U.S. Fish and Wildlife Service. 1985. "Determination of Endangered Status and Critical Habitat Designation for Owens Tui Chub." Federal Register 50(150):31592-31587.