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Photo by Unknown Photographer
Photo Courtesy of Utah Division of Wildlife Resources; Utah Division of Wildlife Resources
Bonytail
Gila elegans
NatureServe conservation status
Global (G-rank): G1
State (S-rank): S1
External links
Species range
Documented captures of adults since 1977 comprise Wahweap Bay, Lake Powell (Gustaveson et al. 1995, USFWS 2002), Gray Canyon, Green River (Tyus et al. 1982, 1987, Moretti et al. 1989), the confluence of the Green and Colorado rivers (Valdez and Williams 1993), and Cataract Canyon, Colorado River (Valdez and Williams 1993).
The historical distribution of this species is poorly documented; few surveys were undertaken prior to the 1950s when the Colorado River system was significantly altered through extensive damming. Interpretation of many records is complicated by the difficulty of distinguishing this species from the sympatric G. robusta, G. cypha, and hybrids of these 3 congeners. Despite the paucity of data, it is generally assumed that this species formerly ranged throughout the Colorado and Green rivers and large tributaries of these rivers (USFWS 2002).
Habitat
This species inhabits main channels of large rivers. Behnke and Benson (1980) stated: "The optimum habitat of bonytail chubs, based on former collections when they were abundant, appears to be the open river areas of relatively uniform depth and current velocity. This type of habitat typically consists of a shifting sand bottom[,] water depths of 3 to 4 feet, and a relatively constant, moderately swift current." Adults are found mainly in pools and eddies with silt and sand or silt and boulder substrates; young occur in still water or shallow pools with silt or sometimes gravel or small rubble substrates (see reviews by Timothy 1983, USFWS 2002).
Food habits
The Bonytail is an opportunistic omnivore with a diet that shifts depending on its age and the availability of food. A Bonytail's diet generally consists of insects, aquatic invertebrates, zooplankton, algae, and plant matter
Reproductive characteristics
Historically, Bonytail spawned in the spring and summer over gravel substrates in the Colorado River system. However, wild reproduction is now rare due to significant habitat changes, leading to the species being maintained largely through hatchery efforts
Threats or limiting factors
The numerous threats to this species are derived primarily from the fundamental ecological changes that have followed the damming of major rivers and tributaries in the Colorado River drainage. Changes in sediment deposition patterns, flow, and temperature caused by dams have resulted in loss and alteration of aquatic habitats and have favored non-native competitors and predators. Increased hybridization among native Gila species may be symptom of changes in habitat and movement patterns, and genetic introgression is now an important threat. Small population sizes resulting from population decline and fragmentation may have implications for the long-term genetic diversity of populations.
