Product Code Database
The humpback chub ( Gila cypha) is a federally protected fish that lived originally in fast waters of the Colorado River system in the United States. This species takes its name from the prominent hump between the head and dorsal fin, which is thought to direct the flow of water over the body and help maintain body position in the swift currents of the Colorado River. The body is almost entirely scaleless, retaining only about 80 mid-lateral scales along the lateral line. The fish is very streamlined, with a thin caudal peduncle 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 10 or more. Maximum recorded length is 38 cm.William F. Sigler and John W. Sigler, Fishes of Utah (University of Utah Press, 1996), pp. 79–83
The humpback chub mostly consumes 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 . 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. The fish's status as an endangered species has inspired a number of 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.
For 2008, the total population of the humpback chub in the Grand Canyon was estimated at 6,000 to 10,000.USGS Grand Canyon Monitoring and Research Center: Humpback 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 drought conditions over the last decade which.
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.
After the Colorado had been extensively modified by dams, the Little Colorado River became the fish's stronghold in the Grand Canyon region. A second population is currently when? 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 were expected to 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 when?, 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 Little Colorado River and Colorado River may have helped the species, but at the same time, drought was lowering the level of Lake Powell 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 Glen Canyon Dam, 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.
|
|
