Flow Recommendations to Benefit Endangered Fishes in the Colorado and Gunnison Rivers. Recovery Program Project Number 54. Final Report

摘要

The upper Colorado River subbasin (the Colorado River and its major tributaries upstream from its confluence with the Green River; the upper Colorado River basin includes all tributaries upstream from Lee Ferry, Arizona) historically supported populations of four native fishes--humpback chub Gila cypha, bonytail G. elegans, Colorado pikeminnow Ptychocheilus lucius, and razorback sucker Xyrauchen texanus--that are currently listed as endangered under the 1973 Endangered Species Act (ESA), as amended. Self-sustaining, wild populations of Colorado pikeminnow and humpback chub still occur in the subbasin, but wild razorback suckers have not been collected since 1995 and wild bonytails have been extirpated. Repatriation programs are underway for razorback sucker and bonytail. These four species are threatened with extinction because of many factors including habitat loss from dike construction, riparian encroachment in the main channel, and construction of water-diversion structures that restrict movement; regulation of river flow, water temperature, and sediment regimes through construction of large reservoirs; introduction of nonnative fishes that are predators or competitors of the native species; and other human-induced perturbations.