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