The Park Service has introduced a satellite population of humpback chub in a Colorado River tributary within Grand Canyon National Park. Time will tell if projects like this can halt the endangered fish’s drift toward extinction in the Grand Canyon.
There are eight native fish species in Grand Canyon National Park. By 1997, four of them -- the Colorado pikeminnow, the razorback sucker, the bonytail chub, and the humpback chub -- were federally listed as endangered species and two others were being considered for listing.
The plight of the Grand Canyon’s highly stressed native fish populations can be attributed to a variety of interacting factors. Scientists believe that the main culprits are fluctuating water flows, unnaturally cold water, competition with and predation by non-native rainbow and brown trout, and harmful parasites such as the Asian tapeworm.
Federal and state natural resource management agencies have grappled with this complex problem, but have yet to devise a comprehensive, internally consistent program for rescuing the endangered fish populations and restoring their habitat. Some scientists and NGOs have argued that nothing short of removing the Glen Canyon Dam and restoring the natural flow of water through the Grand Canyon can insure the long-term survival of threatened and endangered aquatic species. Others advocate less dramatic tactics such as releasing more water from reservoirs, scheduling water releases so as to more closely mimic natural flows, and controlling non-native fish populations.
No recovery plan for the endangered fish species has a good chance to work without increased water releases from upstream impoundments. Environmentalists and park advocates were very happy when Senator Mark Udall (D-CO) recently introduced a bill that would authorize the Bureau of Reclamation to release 5,412.5 acre-feet of unsold water currently stored in the Ruedi Reservoir. If enacted, this legislation would make permanent a temporary water release agreement inked ten years ago to aid recovery of the four endangered fish species.
Emergency measures are needed to make sure that the endangered fish populations survive long enough to derive long-term benefits from the recovery programs now being worked out.
One interesting project of this type is designed to help humpback chub (Gila cypha) get established in new, relatively safe habitat within Grand Canyon National Park. This is important, because significant populations of humpback chub exist in only six locations within the entire Colorado River Basin.
The humpback chub is characteristically found where the water flows deep and fast in the main river and its larger tributaries (the Green River, White River, Yampa River, and Little Colorado River). The fish's trademark hump is actually a streamlined shape that, together with its forked tail, helps it maintain its position in swift-flowing water.
Grand Canyon National Park has some of the best remaining humpback chub habitat as well as the largest remnant population.
In hopes of establishing an additional “satellite population” within the park, the Park Service recently translocated 300 juvenile humpback chub to Shinumo Creek, a Colorado River tributary. The juvenile fish, which might reach a length of 20 inches when fully grown, were captured last year near the mouth of the Little Colorado River. They were then treated for parasites and spent the winter in New Mexico at the U.S. Fish and Wildlife’s Dexter National Fish Hatchery and Technology Center.
Shinumo Creek was deemed a suitable site for a humpback chub translocation experiment because it not only has the right combination of water quality, water temperature, and available food, but also a waterfall barrier just above its confluence with the Colorado River. This barrier prevents non-native trout and other predatory fish from moving into the creek. Some 800 non-native rainbow trout already in the creek were removed before the juvenile humpback chub were released.
It will take years of careful monitoring to determine whether this translocation experiment succeeds in establishing a permanent population of humpback chub in the Shinumo Creek Meanwhile, biologists plan to release more humpback chub in the creek in 2010 and 2011.