Background:
Humpback chub were federally listed as endangered in 1967 and since that time have suffered dramatic declines in number and distribution.  The largest remaining population of these unique fish (several thousand adults) lives near the confluence of the Little Colorado River and Colorado Rivers in Grand Canyon.  Declines in humpback chub numbers are believed to have been caused by dams on the Colorado River which altered water flow and water temperature and allowed introduced fish species which eat small humpback chub to proliferate.

Today humpback chub populations are carefully monitored by the Arizona Game and Fish Department and the Fish and Wildlife Service to identify and remedy specific factors causing

being made to manage water flows from Lake Powell to benefit humpback chub, and research is also being conducted into ways of controlling introduced fish in those areas where juvenile humpback chub live.

Location:
The Little Colorado River enters the mainstem Colorado River in Grand Canyon National Park about 80 miles below Lake Powell.  The lower 8 miles of the Little Colorado River is the main spawning site for humpback chub and is an extremely rugged and remote area accessible only by boat, helicopter or rigorous hiking. 

Approach:
Each spring researchers set hoop nets in the lower 1,200 meters of the Little Colorado River to catch and mark these unique fish.  Captured fish are measured and scanned for the presence of a PIT tag and then released.  PIT tags are small electronic tags about the size of a rice grain that are implanted within the fish.  When a tagged fish is recaptured and scanned, a distinct number is revealed which researchers can use to estimate how many fish are left in the population and how many new fish have been born.  Measurements on water flow and water temperature are also recorded as are catch rates of the other fish species that are present.  All of this information is used to evaluate trends in humpback chub population size. This research is part of a long-term monitoring project for native fish which began in 1987.

Benefits:

This study has revealed past dramatic declines and recent increasing trends in the catch of humpback chub in the Little Colorado River.  It has also proven to be one of the most effective methods of monitoring humpback chub population size.  Continued monitoring will allow researchers to identify management actions, such as planning water releases from Lake Powell that favor humpback chub.  Great care is being taken to preserve this unique species for future generations.

This project is funded by the USGS Grand Canyon Monitoring and Research Center as part of ongoing research activities.

Reports: