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<br />STATUS OF SPECIES <br />ENDANGERED COLORADO RIVER FISHES <br /> <br />The seven State Colorado River Basin watershed is 1112 of the continental United States, <br />receiving the majority of its yield from Rocky Mountain runoff in the spring and early summer <br />and transporting that flow to the mouth of the Colorado River (U.S. Bureau of Reclamation <br />1946). Seasonal variation was considerable, with extremes at the Grand Canyon gauge ranging <br />from an estimated 300,000 cfs on July 8, 1884, to 700 cfs on December 28, 1914 (Boner et aI. <br />1991). Flows between years also varied from wet to dry climatic periods. Fish that evolved <br />in the basin were subject to the concomitant variations in sediment and food resources (U. S, Fish <br />and Wildlife Service 1980; Minckley 1991). <br /> <br />The fish fauna of the basin represent the highest number of endemic fish species (32 species of <br />wh~ch 75% are endemic) of arty basin North America (reviewed by Minckley 1991), with the <br />larger streams and rivers historically dominated by native minnows (cyprinids) and suckers <br />(catostomids) (Minckley et aI. 1986). As the southwest rivers became more arid and seasonal <br />in flow, the fish evolved with high year-ta-year variability and with long-term droughts (Moyle <br />and Herbold 1987). The four "big river" endangered fish of the basin: bony tail chub, Colorado <br />squawfish, humpback chub, and razorback sucker; all occurred in the Grand Canyon before and <br />shortly after Glen Canyon Dam began operating (reviewed by Minckley 1973, 1991). <br /> <br />:; <br /> <br />..-:. <br />f~: <br /> <br />Widespread and sudden declines of the endemic fishes have been related to physical and biotic <br />changes in the habitat of these fishes (U.S. Fish and Wildlife Service 1993a). Miller (1961) <br />chronicled 100 years of drastic changes in the native fishes and rivers of western North America <br />by such factors as deterioration of stream flow, construction of barrier dams, and the <br />introduction and establishment of a host of non-native fish species. <br /> <br />~'.... <br />(.: <br /> <br />HUMPBACK CHUB <br /> <br />General Status <br /> <br />The northern extent of humpback chub's range is the Yampa River, Colorado and the Green <br />River, Utah. The southern extent (historical) is Catclaw Cave, a 750-1100 A.D. archeological <br />site, 24 kilometers south of Hoover Dam on the Colorado River, Arizona (Miller 1955). The <br />species occurs in widely separated, swift water canyon reaches. <br /> <br />r i <br />,~~ <br />~f.i <br />.~~~ <br />~, <br /> <br />In the upper basin, humpback chub were found in pre-impoundment surveys of the Flaming <br />Gorge basin (Guafin et aI. 1960) along with two other species of Gila. Populations of humpback <br />chubs are now found in the areas of (1) Yampa (Yampa River) and Whirlpool (Green River) <br />Canyons of Dinosaur National Monument, (2) Desolation and Gray Canyons of the Green River, <br />(3) Black Rocks area of the Colorado River, (4) Westwater Canyon of the Colorado River, and <br />(5) Cataract Canyon of the Colorado River above Lake Powell (U .S. Fish and Wildlife Service <br />1993a). <br /> <br />.,"; <br />:)'!;: <br />\!, ~" <br /> <br />13 October 1993 Draft biological opinion 2,21-93-F-161 <br /> <br />8 <br />