Gila elegans

In and below Grand Canyon, individuals of Gila elegans, G. cypha, and G. robusta robusta are readily identified by diagnostic morphological and genetic characters (see Gerber et al. 2001). In the upper Colorado River basin, several studies have yielded evidence of hybridization among these taxa in the mainstem Colorado River above Grand Canyon (see Gerber et al. 2001).

Gerber et al. (2001) found that lower Colorado River basin populations of G. cypha exhibit distinct mtDNAs, with only limited introgression of G. elegans into G. cypha, but most sampled upper basin fishes exhibited only G. cypha haplotypes, with some individuals exhibiting mtDNA from G. elegans. The complete absence of G. robusta mtDNA, even in populations of morphologically pure G. robusta, indicates extensive introgression that predates human influence (Gerber et al. 2001).

Hybridization may be a result of a breakdown in reproductive isolating mechanisms caused by habitat and streamflow changes in the basin (Valdez and Clemmer 1982), but it also can be viewed as playing a significant role in generating the great morphological diversity in the genus Gila and enhancing genetic variability and adaptability to the rigorous physical habitats present in the Colorado River Basin (Dowling and DeMarais 1993).

Formerly widespread and common in much of the Colorado River basin; now widely extirpated and very rare, with no known self-sustaining populations; decline apparently has been caused mainly by the effects of dams and exotic fishes, and these continue to threaten the species with extinction.

Bonytails were formerly abundant throughout the Colorado River and its larger tributaries, including the Green River north to the reach now inundated by Flaming Gorge Reservoir in Wyoming and Utah, the Yampa and Gunnison rivers in Colorado, and the Colorado River in Arizona, Colorado, Nevada, and California), and likely also the San Juan River in New Mexico and the Gila and Salt rivers in Arizona (Lee et al. 1980, USFWS 1990, Muth et al. 2000). Documented records exist for Lake Havasu, Lake Mohave, and Grand Canyon in the Lower Colorado River Basin; and Lake Powell, the Colorado River (Cataract Canyon, Green River confluence, Utah; Black Rocks, Colorado), Gunnison River near Delta, Colorado, Green River (Gray Canyon, Utah; Dinosaur National Monument, Colorado and Utah; Hideout Canyon, Utah), and lower Yampa River, Dinosaur National Monument, Colorado), in the Upper Colorado River Basin (USFWS 2002).

An unknown but small number of wild adults exist in Lake Mohave on the mainstem Colorado River of the Lower Colorado River Basin (i.e., downstream of Glen Canyon Dam, Arizona), and there are small numbers of wild individuals in the Green River and upper Colorado River subbasins of the Upper Colorado River Basin (USFWS 2002). USFWS (2002) listed only two locations (Lake Mohave on the Arizona-Nevada border and Lake Havasu along the Arizona-California border) where wild bonytails have been documented since 1990.

As of the early 1990s, populations were being established in urban lakes in Tempe, on the Buenos Aires NWR, and at TNC's Hassayampa Reserve, all in Arizona; plans called for stocking of experimental populations into Arizona streams (Minckley and Deacon 1991).

Currently no self-sustaining populations of bonytail exist in the wild (USFWS 2002).

Threats to the species include habitat modifications resulting from streamflow regulation, dams that function as movement barriers on main-stem rivers, competition with and predation by nonnative fish species, hybridization (possibly), and pesticides and pollutants (USFWS 2002). The significance of, and factors leading to, hybridization with other Gila species are unclear, and this factor is not regarded as an important threat at the present time (USFWS 2002). However, hybridization should be evaluated as bonytails are released into the wild and populations become established (USFWS 2002). Low population size and lack of recruitment are major obstacles to recovery.