|Listed||March 11, 1967|
|Description||Large olive brown chub with a hump behind the head.|
|Habitat||Swift currents and deep channels.|
|Reproduction||Spawns May to July.|
|Threats||Dam construction, competition with non-native fish.|
|Range||Arizona, Colorado, Utah|
The humpback chub, Gila cypha, is a large chub, between 12 and 15 in (30-38 cm) in length, with a prominent dorsal hump behind the head. It has a flat, fleshy snout, and small eyes. It is olive or brown on the back and silvery on the sides and belly. So odd looking is this fish that it has been described as "remarkable" and "bizarre" even in official publications.
Spawning in the Little Colorado River occurs in May to July when the water temperature is 60.8-66.2°F (16-19°C), and May through June in the Black Rocks area of the Colorado River when water temperatures reach 52.7-61.7°F (11.5-16.5°C). Spawning occurs over boulder, sand, and possibly gravel substrates.
The chub's underhanging mouth suggests bottom feeding; it is known to feed on Chironomids, Simuliids, plankton, crustaceans, diatoms, and other small invertebrates.
The humpback is adapted to the Colorado River system, one of the most severe swift-water fish habitats in North America. Its specific habitat requirements are not known, but it has generally been associated with fast currents and deep channels. Juveniles prefer a slower current, a silt substrate, and a depth of less than 3.3 ft (1 m).
The humpback chub was probably found throughout much of the Colorado River basin. It has been documented from the Colorado River from its headwaters in Colorado to its lower reaches along the Arizona-California border; the Green River from its Wyoming headwaters to confluence with the Colorado River in Utah; the lower Yampa River, a Colorado tributary of the Green River; and the White River in Utah.
When Flaming Gorge Dam was completed in Daggett County, Utah, in 1962, the humpback chub was eliminated from long stretches of the Green River above and below the dam. The cold tailwaters of Glen Canyon Dam (built in Coconino County, Arizona) have caused reductions in both the distribution and abundance of humpback chubs in Marble and Grand canyons. Populations are located in the Colorado, Little Colorado, Green, and Yampa rivers. The largest population is located in the Little Colorado River in the Grand Canyon.
The humpback chub has declined significantly since the Flaming Gorge and Glen Canyon dams were completed, but populations were probably lost in the 1930s when the Hoover Dam was built. When the dam reservoirs were filled, cold tailwaters forced out the humpback chub, which prefers warmer waters. Below the dams, water flows were significantly decreased. The U. S. Fish and Wildlife Service (FWS) has determined that any additional diversion of water from the Colorado River would jeopardize the survival of the humpback chub, the bonytail chub (G. elegans ), and the Colorado squaw-fish (Ptychocheilus lucius ).
Conservation and Recovery
When these fishes were granted protection under the Endangered Species Act, the western states threatened a protracted confrontation with the federal government over water rights. In 1984 the FWS convened the Upper Colorado River Basin Coordinating Committee. Members included representatives of the FWS, the Bureau of Reclamation, the states of Colorado, Utah, and Wyoming, and private water development interests.
In 1988 all parties agreed on a recovery program for the Colorado River basin and established a committee to oversee implementation. The unprecedented agreement calls for maintaining an adequate stream flow throughout the system. On the Colorado and Green Rivers prescribed releases from federal reservoirs will provide the needed water. On the Yampa and White Rivers, the FWS will purchase water rights to assure an adequate flow. The agreement also contains provisions for habitat rehabilitation, restocking of native fishes, and continued monitoring of wildlife populations.
A captive propagation program has been established to stock reclaimed portions of the Colorado River with native fishes. Fish hatcheries in the region, such as Rifle Falls State Fish Hatchery and the Hotchkiss National Fish Hatchery, will probably be expanded to include facilities for the humpback chub. In 1989 in a multi-agency cooperative effort, 1,800 humpbacks were captured in the Little Colorado; 450 were tagged with radio transponders to enable biologists to track the fish's movements in the river.
The second revised Recovery Plan for the species, released in 1990, noted that the recovery goal is the protection or restoration of five viable, self-sustaining populations within the Colorado River basin and the protection of the habitat utilized by these populations.
Downlisting will occur when these five populations have been located or reestablished. To achieve this goal, the FWS recommended a number of actions, including the resolution of taxonomic problems in defining the populations of the Colorado Basin gila ; the identification and definition of humpback chub populations; and research into the life history and ecological requirements of the fish. The plan also calls for the protection of humpback chub populations and their habitats, the assessment of potential reintroduction and augmentation sites, and the implementation of stocking. Promoting and encouraging improved communication and information dissemination was also advised.
On March 21, 1994, the FWS published the final rule designating Critical Habitat for the Humpback Chub in portions of the Upper Basin of the Colorado, Green, and Yampa rivers; and in the Colorado and Little Colorado rivers in the Lower Basin.
Regional Office of Endangered Species
U.S. Fish and Wildlife Service
P. O. Box 25486
Denver Federal Center Denver, Colorado 80225
U.S. Fish and Wildlife Service. 1979. "Humpback Chub Recovery Plan." U.S. Fish and Wildlife Service, Albuquerque.