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