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(Student's t - 0.01; P < 0.55) than their movement in eddies and backwaters (n - 14; mean - 32.05 m/h; SD - 28.85). This similarity in movement between the two habitat categories does not allow us to hypothesize on wintertime resting and feeding habitat for adult razorback suckers. Selection of wintertime'microhabitat by adult razorback suckers also appears driven by low average and near-bottom velocities, but the depth requirement does not seem as critical as for adult Colorado squawfish; minimum average depth used by razorback suckers was 2.0 feet. These fish used similar watercolumn depths and velocities in three habitat categories under ice and ice-free conditions (Table 2). The fish consistently used areas of low bottom velocity which were not necessarily the deepest parts of the river channel. Webelieve both adult razorback suckers and Colorado squawfish were frequently positioned near the river bottom where velocities were low, although river turbidity did not allow us to observe them directly. Although the dominant and secondary substrates associated with both species was usually sand or silt, adult razorback suckers appeared to use cobble areas more frequently than adult Colorado squawfish, although this is reflected only as a secondary substrate in eddies. We also recognized that these fish were commonly associated with an instream cover element. Adult razorback suckers, like adult Colorado squawfish, were frequently seen in slow runs and slackwaters immediately downstream of sand shoals that appeared to slow water velocity at the fish location. Razorback suckers were often located in small depressions.or troughs created by either sand waves or cobble piles. LITERATURE CITED Biological Sub-Committee. 1984. Rare and endangered Colorado River fishes sensitive areas. A report to the Upper Colorado River Basin Coordinating Committee. 23 pp. McAda, C. 1977. Aspects of the life history of three catostomids native to the upper Colorado River Basin. M.S. Thesis, Utah State University, Logan. 117 pp- Tyus, H.M. 1982. Fish radiotelemetry: Theory and application for high conductivity rivers. U.S. Fish and Wildlife Service, National Ecology Center, Report FWS/OBS-82/38, (National Technical Information Service P883-166058), Fort Collins, Colorado. Tyus, H.M. 1988. Long-term retention of implanted transmitters in Colorado squawfish and razorback suckers. North American Journal of Fisheries Management 8:264-267. Valdez, R., H. Tyus, and L.Kaeding. 1981. Carlin tags on Colorado River Endangered Fishes. Transactions American Fisheries Society, Bonneville Chapter 1981:78-82. 46