The humpback chub (''Gila cypha'') is a federally protected fish that lived originally in fast waters of the

Colorado River The Colorado River ( es, Río Colorado) is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and northern Mexico. The river drains an expansive, arid drainage basin, watershed that encompasses parts of ...

system in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

. This species takes its name from the prominent hump between the head and

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

, which is thought to direct the flow of water over the body and help maintain body position in the swift currents of the Colorado. The body is almost entirely scaleless, retaining only about 80 mid-lateral scales along the

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial ...

. The fish is very streamlined, with a thin

caudal peduncle Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

and a deeply forked tail. The back is a light olive gray, the sides silver, and the belly white. The dorsal fin usually has nine rays, and the

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

10 or more. Maximum recorded length is 38 cm. The humpback chub mostly consumes

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s and, to a lesser extent, other fish. They feed at all levels from the bottom to the surface. The species spawns from April through June, at water temperatures of 19-21 °C. The males develop nuptial tubercles on the head and paired fins. The fish spawn in slower-moving backwaters, typically over a substrate of cobbles or boulders. Young fish stay near shore and in quiet areas, preferring slightly more turbid water.Minckley, W.L. 1973. Fishes of Arizona. Arizona Game and Fish Department, Phoenix. pp. 98-99. The humpback chub's population in the Colorado has been reduced dramatically, primarily due to habitat loss, such as the construction of

Glen Canyon Dam Glen Canyon Dam is a concrete arch-gravity dam on the Colorado River in northern Arizona, United States, near the town of Page, Arizona, Page. The high dam was built by the U.S. Bureau of Reclamation (USBR) from 1956 to 1966 and forms Lake Powe ...

. The fish's status as an endangered species has inspired a number of costly and controversial management measures, such as altering the operation of Glen Canyon Dam and removal of non-native predators.Tobin, Mitch. ''Endangered: Biodiversity on the Brink.'' Golden, CO: Fulcrum, 2010.

Description

The humpback chub has a streamlined body, with a concave skull on its dorsum. The caudal peduncle is thin and somewhat pencil-like but not greatly elongated, where the length of the caudle peduncle divided by length of head is less than 1.0. The head length divided by the caudal peduncle is less than 5.0. The scales are embedded deeply across the surface of the fish, especially on hump. The fins are large and curved, and the origin of the dorsal are about equidistant between the snout and caudal fin base. The mouth is inferior, and overhung by the snout. The pharyngeal arch is small, with a short lower ramus.

Range

The humpback chub historically ranged from below present-day Hoover Dam in the Colorado River upstream into Colorado, and in the larger portions of Colorado River tributaries in Arizona, Utah, Colorado, and Wyoming. Presently the species is restricted to six population centers in: 1) the Colorado and Little Colorado rivers in Grand Canyon, Arizona; 2) the Colorado River in Cataract Canyon, Utah; 3) the Colorado River in Black Rocks, Colorado, and Westwater Canyon, Utah; 4) the Green River in Desolation and Gray canyons, Utah; 5) the Green River in Dinosaur National Monument, Colorado and Utah; 6) and the Yampa River in Dinosaur National Monument, Colorado.Arizona Game and Fish Department. 1988. Threatened Native Wildlife in Arizona. Arizona Game and Fish Department Publication. Phoenix, Arizona. p. 4. The Humpback Chub is found in Arizona at and around Coconino County, Colorado and Little Colorado rivers in the Grand Canyon.

Habitat

In general, species persists only in turbulent, high gradient, canyon-bound reaches of large rivers in the Colorado River Basin. The young prefer shallow, low-velocity nearshore pools in the Little Colorado River, and progressively move to deeper, faster areas with increasing size and age. In the Colorado River in Grand Canyon, young-of-year are found in backwater and other near-shore, slow-velocity sites, with similar ontogenetic tendencies. Adults in the Colorado River in Grand Canyon and in the Upper Basin are associated with large eddy complexes. Humpback chub appear to be more active at night.Kaeding, L.R., and M.A. Zimmermann. 1983. Life history and ecology of the humpback chub in the Little Colorado and Colorado rivers of the Grand Canyon. Transactions of the American Fisheries Society 112:577-594.

Parasites and Diseases

The population in the Grand Canyon has been previously infested with the parasitic copepod ''Lernaea cyprinacea'', and Asian tapeworm, '' Bothriocephalus acheilognathi''.Angradi, T.R., R.W. Clarkson, D.A. Kinsolving, D.M. Kubly, S.A. Morgensen. 1992. Glen Canyon Dam and the Colorado River: responses of the aquatic biota to dam operations. Prepared for the Bureau of Reclamation, Upper Colorado Region, Glen Canyon Environmental Studies, Flagstaff, Arizona. Cooperative Agreement No. 9-FC-40-07940. Arizona Game and Fish Department, Phoenix. pp. 155. Kaeding and Zimmermann also reported 13 species of bacteria, six protozoans, and the fungus Saprolegnia to infect humpback chub.

Population Trends

The historic range of the humpback chub is uncertain, but the distribution was presumably more contiguous than in the present. There were possible populations in and below the Flaming Gorge that were likely destroyed by the poisoning of the Green River associated with the construction of the Flaming Gorge Reservoir. The fish's distribution within the Grand Canyon has contracted since the construction of

. For 2008 the total population of the humpback chub in the Grand Canyon is estimated at 6,000 to 10,000.USGS Grand Canyon Monitoring and Research Center
Humpbck Chub
November 2011 This is a 50-percent increase over the estimation of 2001 and a reversal of the declining trend between 1989 and 2001. It seems that a combination of human causes and natural events stabilized the population, particularly the experimental flooding of the canyon and the increase in water temperatures due to draught conditions over the last decade.

Management and Conservation

Threats: altered hydrology and cold tailwater releases from reservoirs; Predation by and competition with nonnative fishes; and, parasitism. Management Needs: ameliorate effects of reservoirs; ameliorate effects of nonnative fish and parasite sources in chub waters; monitor status of all populations. Also need to be concerned about genetic isolation of populations by dams. The humpback chub's status as an endangered species has prompted elaborate and expensive programs to restore its numbers, largely by modifying the releases from Glen Canyon Dam, creating artificial floods to replicate historic conditions in the Colorado, and removal of non-native predators, such as rainbow trout. Effective April 20, 1994, seven reaches of the Colorado River System (totaling 379 miles) were designated as Critical Habitat for ''Gila cypha''. The Grand Canyon Protection Act of 1992 reduced stage fluctuation of water releases from Glen Canyon Dam. Glen Canyon Environmental Studies Phase I (1984–1987) and Phase II (1990–1995) research data used in development of Glen Canyon Dam Environmental Impact Statement and Biological Opinion. Upper Colorado River Basin Recovery and Implementation Plan guides recovery efforts for the species in the Upper Basin. Gila cypha IMGP1312

After the Colorado had been extensively modified by dams, the

Little Colorado River The Little Colorado River () is a tributary of the Colorado River in the U.S. state of Arizona, providing the principal drainage from the Painted Desert region. Together with its major tributary, the Puerco River, it drains an area of about in ...

became the fish's stronghold in Grand Canyon region. A second population is currently established in Shinumo Creek, another tributary to the Colorado River inside Grand Canyon National Park. The first 300 fish were released in Shinumo Creek in June 2009. Over the following two years additional young chubs will be released there. Federal officials have tried a number of experimental releases from Glen Canyon Dam in an attempt to replicate historic conditions and restore sandbars, beaches, and backwaters downstream. The first flood began on March 26, 1996, when Interior Secretary Bruce Babbitt stood before a large gathering of media and opened the first of four outlet tubes to begin the imitation inundation. The 1996 flood released nearly per second, enough to fill the Empire State Building or Sears Tower in 20 minutes, drained from Lake Powell, and dropped the reservoir level by more than three feet. Initially, it appeared that the flood was a success, with sandbars and backwaters created downstream, but as the dam's operations returned to normal, the Colorado ate away at the new habitat and reversed the gains. Several other fake floods have been tried since 1996, with the releases now timed to coincide with an input of sediment from tributaries, but the results have been disappointing. In recent years, the number of humpback chub in the Grand Canyon region has increased significantly, but the reasons are unclear. Removal of non-native fish near the confluence of the

and Colorado River may have helped the species, but at the same time, drought was lowering the level of

Lake Powell Lake Powell is an artificial reservoir on the Colorado River in Utah and Arizona, United States. It is a major vacation destination visited by approximately two million people every year. It is the second largest artificial reservoir by maximum ...

and causing water released from Glen Canyon Dam to be much warmer than normal. Typically, water released from the dam is too cold for chub to reproduce. Introduced smallmouth bass have been a predatory threat to humpback chub above the

, but had not been able to get beyond Lake Powell. But as of 2022, smallmouth bass have been found below Glen Canyon Dam, possibly as a result of the low water level at Colorado River and Lake Powell.

References

* Tobin, Mitch. ''Endangered: Biodiversity on the Brink.'' Golden, CO: Fulcrum, 2010. * William F. Sigler and John W. Sigler, ''Fishes of Utah'' (University of Utah Press, 1996), pp. 79–83 *
USFWS Environmental Conservation Online System page for Humpback chubUSFWS Upper Colorado Endangered Fish Recovery ProgramUSFWS List of Fish Listed under Endangered Species Act
* National Park Service:

' (accessed on 2009-09-01)

External links

List of Arizona Native Fishes

Arizona Desert Museum
United States Fish and Wildlife Service Rule Reclassifying the Humpback Chub from Endangered to Threatened (2021)
{{Taxonbar, from=Q139333 Chubs (fish) Gila (fish) Fish of the Western United States Cyprinid fish of North America Endangered fish Taxa named by Robert Rush Miller Fish described in 1946 ESA endangered species Freshwater fish of North America