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<br />001706 <br /> <br />Revised Supplemental Draft Environmental Assessment-Chapter 3-Affected <br />Environment and Environmental Consequences <br /> <br />between Palisade and Lorna within the next 5 years. The affected reach is within <br />designated critical habitat for the Colorado pikeminnow and razorback sucker. These <br />fish are known to occupy habitat downstream from the dam, but the Colorado <br />pikeminnow is absent in the 50 miles of its historic range from the Price-Stubb Diversion <br />Dam upstream to Rifle, and razorback sucker are extremely rare. <br />A dramatic decline in razorback suckers occurred between 1974 and 1991 in the <br />Colorado River. In 1991 and 1992,28 adult razorback suckers were collected from <br />isolated ponds adjacent to the Colorado River near DeBeque, Colorado. No young <br />razorback suckers have been collected in recent surveys of the Colorado River. <br /> <br />Other native fish species found in the Colorado River include flannelmouth sucker, <br />bluehead sucker, mountain sucker, and roundtail chub. Fish surveys upstream and <br />downstream of the dam show a higher composition of native than nonnative species <br />upstream of the dam, and many of the nonnative species found downstream of the dam <br />are absent upstream (Wydoski, 1994). Nonnative fish species that are absent upstream <br />include channel catfish, northern pike, red shiner, largemouth bass, bluegill, and black <br />crappie. Black bullhead,smallmouth bass, and green sunfish are rare (Service, 1998). <br /> <br />Predation by and competition with nonnative fishes is believed to be significant factors in <br />the decline ofthe endangered Colorado River fishes. Channel catfish and green sunfish, <br />along with other sport fish such as smallmouth and largemouth bass, and northern pike, <br />are predators of endangered fish. Off channel ponds have been identified as a source of <br />many of the nonnative sport fishes that occur in the river and endangered fish nursery <br />areas. Small nonnative fish (minnows and shiners) are assumed to be significant <br />predators of fish larvae as well as important competitors (Wydoski, 1998). Fathead <br />minnow and sand shiners are more common downstream from the dam, and red shiners <br />have been found downstream of the dam, but not upstream (Service, 1998). The <br />distribution of native and nonnative fish upstream and downstream of the dam indicate <br />the dam also serves as a barrier to nonnative fish, and may help control the spread of <br />nonnative fish upstream. <br /> <br />One radio-tagged Colorado pikeminnow was documented using the scour hole below the <br />Price-Stubb Diversion Dam in 1986 and 1987 (Burdick, 2002). The portion of the <br />Colorado River and its 100 year floodplain between GVIC Diversion Dam and the Grand <br />Valley Project Diversion Dam (including the Price-Stubb Diversion Dam) are inCluded in <br />the designated critical habitat for the Colorado pikeminnow and razorback sucker. <br /> <br />Impacts <br /> <br />No Action: If no passage is provided, a self-sustaining population of endangered <br />fish would be less likely to develop via a natural upstream recolonization. Even if <br />stocked fish mature, and succeed in reproducing upstream, young fish that drift or move <br />downstream of the dam could not return as adults. If native fish cannot access upstream <br />habitat, related Recovery Program efforts to acquire and restore floodplain habitat, stock <br />endangered fish, and remove nonnative fishes would be less effective. <br /> <br />47 <br />