 Background:
Humpback chub were federally listed as endangered in 1967 and since that
time have suffered extreme 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.
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Today humpback chub populations are carefully monitored by the Arizona
Game and Fish Department and the Fish and Wildlife Service to identify
and address specific factors causing continued population declines. Efforts
are 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:
Long-term, standardized monitoring of the Little Colorado River fish community allows researchers to track changes in trends over long periods of time. Hoop net monitoring has proven to be one of the most
effective methods of monitoring humpback chub population size in the Little Colorado River. 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.
For more information
contact
Brian C. Clark
Arizona Game and Fish Department
506 N. Grant Street,
Suite L, Flagstaff, AZ 86004
(928) 226-7677 bclark@azgfd.gov
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