7066 - Laserfiche WebLink

Home Browse Search

similar to that of the squawfish in the main river channels of the Colorado and Green rivers. Chubs were restricted to swift, deepwater areas, mainly in canyons, and did not occur far up tributary streams. The greatest known concentration of this species now occurs in the lower few miles of the Little Colorado River, in the Grand Canyon area of Arizona. Perhaps the releases of cold water from Lake Powell have forced most of the humpback chubs from the main Colo- rado River in Grand Canyon into the warmer Little Colorado. In the upper basin, humpback chubs occur sporadi- cally in the Colorado River up to Palisade, Colo- rado, about 10 miles above Grand Junction. The greatest concentration occurs in the Black Rocks area of Ruby Canyon, about 25 miles below Grand Junction, where turbulent flows create a pool almost 60 feet deep at low water levels. In the Green River, the humpback chub occurs below the mouth of the Yampa, and is concentrated in the Desolation Canyon area. It has been recorded from the lower Yampa River in Dinosaur National Monument. Causes of Decline Because the humpback chub had a restricted dis- tribution and thus was always relatively rare, there is not much evidence of a decline except where reser- voirs were constructed. The deepwater habitat favored by this species is not easily sampled by standard methods of fish collecting. As sampling techniques improve and more is learned about humpback chubs, more populations probably will be discovered. The most abundant known population, in the Little Colorado River, was not discovered until 1975. There has been considerable concern that the humpback chub may lose its identity as a result of hybridization with bonytail and roundtail chubs. It now seems probable that most of the specimens formerly believed to be hybrids actually showed only normal variation in the degree of hump development. Some specimens, however, probably are hybrids. The bony- tail chub now is so rare that it can be discounted as a significant source of possible hybridization. The roundtail chub, however, is common in the Colorado River in Colorado and occurs with the humpback chub in Ruby Canyon, where some intermediate (hybrid?) specimens have been taken. The roundtail chub is absent or occurs rarely in humpback chub habitat in the Green River or in the Little Colorado River. Thus, overall, the threat to the integrity of the humpback chub species from hybridization is probably not as great as was once believed. The deepwater areas preferred by humpback chubs are also a preferred habitat for non-native channel catfish. Large populations of catfish and carp share the Ruby Canyon habitat with the humpback chub. Prospects for the Future A Recovery Plan has been written for the hump- back chub, but, as with the squawfish, the main emphasis was placed on hatchery propagation as the only clearly defined technique to increase abundance. Humpback chubs have been transported to the Willow Beach National Fish Hatchery, Arizona, for an attempt at artificial propagation. It is likely that addi- tional populations will be found when more of the deepwater canyon areas in the upper basin are more thoroughly sampled. Fishermen can be of assistance in this regard by reporting catches of humpback chubs. Good humpback chub habitat is also good channel cat- fish habitat, and the chub can be caught on the same bait often used for catfish. Humpback chubs must, of course, be released, but the Colorado Division of Wildlife should be notified of the catch, particu- larly if it is outside of the Ruby Canyon area of the Colorado River. A documented angler's catch (with a photo, if possible) may provide new distri- bution records and lead to the discovery of new populations of this rare fish. A humpback chub preservation and restoration program is yet to be started, but it will probably consist of the identification of all areas where populations still occur, so that the present environ- mental conditions in those areas can be maintained. It would be extremely difficult to establish humpback chubs where they do not now exist. They may now inhabit all suitable areas where self-sustaining populations can be maintained under present environ- mental conditions. The outlook is not encouraging for expanding the distribution and abundance of humpback chubs by establishing new self-sustaining populations. Their habitat requirements are highly restrictive. Possibilities should be looked for, however, where deep channel areas have been created by bridge or highway construction, forming suitable habitat beyond the present limits of distribution. In such situations, introduction of the humpback chub might result in the successful establishment of a new population. Valuable information could be obtained from experimentation designed to establish new popu- lations. There is little doubt that the humpback 17