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<br />STATUS OF SPECIES <br /> <br />~. <br />~ <br /> <br /><'; <br /> <br />The seven-State Colorado River Basin watershed is 1/12 of the continental United' States, <br />receiving,themajority of its_yield from Rocky ,Mountailuunoff 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). Historically, seasonal variations in the free flowing River were considerable, with <br />extremes at the Grand Canyon gauge ranging from an ,estimated .300,000 cfs on July 8, 1884, <br />to 700 cfs on December 28, 1914 (Boner etal. 1991). Flows. between years also varied from <br />wet to dry climatic periods. Fish that evolved in. the basin were subject to the concomitant <br />variations in sedimenLand food resources (U.S. Fish and Wildlife Service 1980; Minckley <br />1991). <br /> <br />, <br />~ <br />~ <br />~ <br />" <br /> <br />ENDANGERED COLORADO RIVER FISHES <br /> <br />< ~ <br /> <br />~~. <br /> <br />The fish fauna of the basin represent the highest number of endemic fish species (32 species of <br />which 75% are endemic) of any basin in 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-to-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; U.S. Fish <br />and Wildlife Service 1994a). <br /> <br />-~~. <br />r~~ <br />!t <br />". <br />:~ <br /> <br />,;., <br /> <br />'. <br />':.' <br /> <br />','-.~ <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 (Deacon and Minckley 1991; U.S. Fish and Wildlife <br />Service 1994a). Miller (1961) chronicled 100 years of drastic changes in the native fishes and <br />rivers of western North America by such factors as deterioration of stream flow, construction <br />of barrier dams, and the introduction and establishment of a host of non-native fish species. <br /> <br />, <br />~; <br /> <br />"'.; <br /> <br />>~~ <br /> <br />HUMPBACK CHUB <br /> <br />'-~~ <br /> <br />'" <br /> <br />r8 <br /> <br />General Status <br /> <br />r.~ <br />~r;; <br />W.;;; <br />~; <br />iit: <br />...}\;, <br />;g~- <br />~~t <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 (Ian) south of Hoover Dam on the Colorado River, Arizona (Miller 1955). <br />The species occurs in widely separated, swift water canyon reaches. <br /> <br />.'~'.: <br />.,: <br /> <br />In the upper basin,. humpback chub were found in pre-impoundment s.urveys 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 Canyon (Yampa River) and Whirlpool Canyon <br />(Green River),of Dinosaur National Monument, (2).Desolation Canyon and Gray Canyon of the <br />Green River, (3) Black Rocks area of the Colorado River, (4) Westwater Canyon of the <br />Colorado River, and (5) Cataract Canyon of the Colorado River above Lake Powell (U.S. Fish <br />and Wildlife Service 1994a). <br /> <br />15 December 1994 final biological opinion 2-21-93-F-167 <br /> <br />7 <br />