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EXECUTIVE SUMMARY <br />This study was established to generate baseline information about the fish community and <br />habitat characteristics of the Colorado River between Palisade and Rifle. Although this section of the <br />Colorado River is designated critical habitat for both Colorado squawfish and razorback suckers, no <br />squawfish are known to occur here and only a small remnant population of razorback suckers still <br />exists in a floodplain pond. The Recovery Program expects this river section to be repopulated with <br />Colorado squawfish and razorback suckers following construction of fish passage structures on <br />existing migration barriers (Highline dam and Price -Stub dam). The data collected in this study are <br />meant to provide an assessment of habitat suitability and the potential for reestablishment of these two <br />endangered fish in this river section. Also these data are meant to provide a basis for <br />recommendations for management activities pending for this river section, i.e., supplemental stocking <br />of endangered Colorado squawfish and razorback sucker and instream flow recommendations. <br />A great deal of effort was spent sampling the main channel fish community because fish <br />community structure can be strongly influenced by habitat availability. The presence or absence of <br />keystone species, usually top predators can also affect fish population dynamics. Of the potential <br />large predator species found in the basin (Colorado squawfish, northern pike, channel catfish, small <br />or largemouth bass and brown trout) only a very few individuals of small -sized smallmouth and <br />largemouth bass and brown trout were collected in this study. Brown trout were very rare below <br />Parachute. Due to a lack of predatory pressures, it was felt that fish biomass was at carrying capacity <br />and certain aspects of the fish community structure, (species composition, size and age structure), <br />were primarily regulated by hydrology, geomorphology and forage productivity of the river reach. <br />Four stations were electrofished in March 1994 and two in March 1995. In 1994, 83% of <br />12,646 fish collected were native species, in 1995 85% of 9,458 fish collected were native. <br />Flannelmouth and bluehead sucker comprised 63% of fish community. A large difference was <br />observed for species composition, size and age structure of the fish communities for Debeque Canyon <br />and Parachute in both years. Debeque had a high percentage (38 %) of roundtail chub compared to <br />Parachute (5 %), the percent of fish under 30 cm was 48% in Debeque Canyon versus 5% at <br />Parachute and total estimated fish biomass was 116 kg/ha at Debeque compared to 330 kg/ha at <br />Parachute in 1994. These results indicate that fish forage potential is greater in Debeque Canyon for <br />small and median sized squawfish, even though fish biomass is greater in Parachute <br />The difference between fish community structure at Debeque Canyon and Parachute led to <br />speculation that habitat differences were primarily responsible. The reduced biomass at Debeque <br />Canyon could be a result of reduced riffle quality or increased width/depth ratios. The increased <br />number of young -of -year and juvenile fish at Debeque Canyon suggest higher abundance of low <br />velocity habitats there. A lack of habitat availability for adult Colorado squawfish and razorback <br />sucker was not suggested by Wick and Hawkins (1986) habitat suitability index or by gross <br />observation, while measurements and observation about spawning and nursery habitat availability <br />were more inconclusive. <br />I V" <br />t <br />