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Photo Courtesy of Utah Division of Wildlife Resources
Humpback Chub
Gila cypha
NatureServe conservation status
Global (G-rank): G1
State (S-rank): S2
- Reason: Three populations are considered to be extant in Utah. The distribution and abundance of this species is believed to have declined radically from historical levels as a result of fundamental changes to the ecological conditions of the Colorado River system.
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General information
The humpback chub, Gila cypha, is a rare minnow native to the upper Colorado River system. Humpback chub originally thrived in the fast, deep, white-water areas of the Colorado River and its major tributaries, but flow alterations, which have changed the turbidity, volume, current speed, and temperature of the water in those rivers, have had significant negative impacts on the species. In fact, humpback chub in Utah are now confined to a few white-water areas in the Colorado, Green, and White Rivers. Because of the severe declines in humpback chub numbers and distribution, the species is Federally listed as endangered.
Humpback chub primarily eat insects and other invertebrates, but algae and fishes are occasionally consumed. The species spawns during the spring and summer in shallow, backwater areas with cobble substrate. Young humpback chub remain in these slow, shallow, turbid habitats until they are large enough to move into white-water areas.
Species range
Populations occur in the Colorado River in Westwater Canyon and Cataract Canyon and in the Green River in Desolation and Gray canyons (USFWS 2002). Historically the occupied range was larger; records suggest that much, if not all, of the Green River and perhaps some of the major tributaries (e.g., the White River) supported populations.
Migration
In the Little Colorado River, Arizona, some individuals moved upriver in early spring and made a slow, protracted postreproductive movement downstream (Douglas and Marsh 1996).
Habitat
This species occurs in large rivers, primarily in canyon-bound reaches. Spawning habitat is deep, swift water over clean gravel or cobbles. Adults are often found in deep, recirculating eddies, although other deep water habitats are used. Sub-adults occupy rather shallow water with slow currents. (see Berg 1983, USFWS 2002).
Food habits
More information needed. Known to feed on planktonic crustaceans and algae. See Tyus and Minckley (1988) for possible importance of Mormon cricket as food source.
Ecology
Recaptures and radio telemetry indicate limited movements, particularly from summer through winter (Douglas and Marsh 1996); recaptures/relocations averaged 1.6 km or less from release site after up to 434 days (Valdez and Clemmer 1982).
Reproductive characteristics
Spawns in spring at reported temperatures of 16-19 C (Arizona) and 11.5-16 C (Colorado), shortly after peak flow. USFWS (Federal Register, 21 March 1994) reported that spawning occurs when water temperatures approach 20 C. Individuals in reproductive condition have been captured usually in May, June, or July, the time depending on location. Adults are at least 2-3 years old. Maximum life-span is 20-30 years or more.
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.
References
- Biotics Database. 2005. Utah Division of Wildlife Resources, NatureServe, and the network of Natural Heritage Programs and Conservation Data Centers.
- Sigler, W. F. and J. W. Sigler. 1996. Fishes of Utah[:] a natural history. University of Utah Press. Salt Lake City. 375 pp.
