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~ ~ <br />3 <br />sample size and lack of similar work in other locations in the Green River <br />basin make these data difficult to interpret. <br />This study evaluated the relative abundance, age, growth, condition, and <br />diet of channel catfish from different habitats in the Green and Yampa rivers, <br />to test the hypothesis that environmental conditions in the Green River basin <br />may not be optimal for growth in this species. We discuss our findings <br />relative to the potential effect of channel catfish on recovery of endangered <br />Colorado River fishes. <br />MATERIALS AND METHODS--Channel catfish were captured by U.S. Fish and <br />Wildlife Service personnel during 1987 and 1988 using electrofishing, seining, <br />and angling techniques. A sample of catfish was obtained in each of seven <br />reaches (Fig. 1) between River Kilometer (RK) 35 and 552 of the Green River, <br />and one reach (0-74km) of the Yampa River in Dinosaur National Monument. These <br />reaches were selected for differences in habitat types, including low-gradient <br />river reaches (average drop in water surface elevation = 0.2 to 0.4 m/km), <br />predominated by sand and silt substrates (A, B, E, and F in Fig. 1) versus <br />higher gradient reaches (1.3 to 2.1 m/km drop in elevation), predominated by <br />boulder and cobble substrates (reaches C, D, and G, and Yampa River in <br />Dinosaur National Monument; Fig. 1). The relative abundance of adult channel <br />catfish was evaluated by spring sampling of shoreline habitats and involved <br />continuous downstream coverage with a pulsed DC unit. Angling with cricket <br />and worm-baited hooks was also conducted in July and August at selected eddy <br />habitats in lower Yampa River, Desolation and Gray canyons, and in strata E <br />and F (Fig. 1). <br />