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• BASIS FOR OPINION <br />COLORADO SQUAWFISH <br />Early records indicate t~iat the Colorado squawfish was once abundant ' <br />throughout the Colorado River system. It was abundant over all of its range <br />prior to the 1850's (Seethaler, 1978). The present range of the Colorado <br />squawfish is restricted to the upper~Colorado River basin. It 1s found <br />inhabiting about 345 miles of the main stem Green River from the mouth of the <br />Yampa River downstream to the confluence of the Creen and Colorado Rivers. <br />Its range also extends 140 miles up the Yampa River and 156 miles up the White <br />River, the two major tributaries of the Green River. In the mainstem Colorado <br />River, it is currently found from Lake Powell extending about 201 miles <br />upstream to Palisade, Colorado, and in the lower 33 miles of the Gunnison <br />River, a tributary to the mainstem Colorado River (Fish and Wildlife Service, <br />1982). <br />Decline of populations of the squawfish correlates very closely with the <br />construction of dame and reservoirs and the removal of water from the Colorado <br />River system. Colorado squawfish evolved in and apparently require stream <br />habitat conditions typified by great seasonal fluctuations in flow and <br />turbidity, coupled with warmer water temperatures in the summer. <br />~ Additionally, it appears that squawfish require relatively unrestricted <br />movement to satisfy all of their life history requirements. Movement of adult <br />squawfish appears to be related to flow, temperature, Feeding and spawning <br />behavior. <br />The life stages that appear to be most critical are from egg fertilization <br />through its first year of life. It has been demonstrated that these phases of <br />Colorado squawfish development are also closely tied to some specific habitat <br />requirements. It is imperative that proper flows and temperatures are <br />provided during these essential life stages. The conservation measures <br />outlined below will help meet the habitat requirements of the Colorado <br />squawfish, thus offsetting project-related impacts and the likelihood of <br />jeopardy for the species. <br />HUMPBACK CHUB <br />Bumpback chub generally do not make migrational movements in the upper <br />Colorado River and tend to reside throughout the year within a limited reach <br />of river. Bumpback chub are found inhabiting narrow, deep canyon areas, and <br />are relatively restricted in distribution. They seldom leave their canyon <br />habitat (FWS, 1982). While the humpback chub are still occasionally found <br />dispersed in the Green and Yampa Rivers, the only major populations of <br />humpback chub conclusively known to exist in the upper Colorado River basin <br />are located in Black Rocks and Westwater Canyons on the Colorado River. <br />Conservation measures outlined below will contribute to providing proper <br />habitat conditions for humpback chub, thus offsetting the likelihood of <br />jeopardy for the species. <br />2 <br />