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<br />~ . <br /> <br />" r-. <br /> <br />I <br />I <br />l <br />, <br /> <br />'j <br />i <br />I <br />! <br /> <br />',- <br /> <br />Although the exact spawning sites were not located, lack of movement by <br />the radio-tagged fish and no apparent movement by other humpback chub <br />strongly suggests that spawning occurs within the 3-km confines of Black <br />Rocks. Spawning sites are probably on submerged cobble bars near the <br />upstream end of the area. Additional study is needed to ascertain spawn- <br />ing conditions of a species that appears to spawn at or near peak <br />runoff. <br /> <br />CONCLUSIONS <br /> <br />Radiotelemetry appears to be a feasible tool to aid in assessing <br />movement and habitat use of humpback chub. Their relatively sedentary <br />mode precludes extensive boat and aerial searches throughout the river. <br />Much can be learned about the behavior of the species with radio- <br />telemetry. <br /> <br />Although fish modules should not exceed 5 g in weight, a stronger <br />and longer-lasting transmitter and stronger receivers are needed to more <br />accurately assess behavior and fish use of the deep river regions, and to <br />continue monitoring the species beyond the summer months. <br /> <br />Radiotelemetry in the upper Colorado River indicates that humpback <br />chub occupy restricted areas of the river, characterized by deep, swift <br />water and substrates of bedrock, boulder and sand. Apparently, the chubs <br />rarely leave these areas and spawn, rear and mature within their <br />confines. <br /> <br />Although restricted areas such as Black Rocks exhibit deep and swift <br />water, the chubs prefer to remain in small pools and eddies with slow <br />water. These quiet-water microhabitats provide the chubs with resting, <br />feeding and rearing areas in the relative security of adjacent deep and <br />swift water that excludes most other native as well as many non-native <br />fishes. Flow reductions in the upper Colorado River appear to be <br />affecting these restricted habitats as indicated by the presence of <br />apparent humpback-roundtail chub hybrids and an apparent invasion of <br />these areas by several competitive and predaceous non-native fish <br />species.. <br /> <br />. <br /> <br />38 <br />