Humpback Chub - Management and Conservation

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, highly controversial, 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 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 337,000 US gallons (1,280,000 L) per second, enough to fill the Empire State Building or Sears Tower in 20 minutes, drained 117 billion US gallons (440,000,000 m3) 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 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.