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EXECUTIVE SUMMARY This report presents information on movements and, to a limited extent, habitat use by adult and juvenile razorback sucker Xyrauchen texanus as well as a comparison of growth and survival of juvenile razorback sucker between main-channel and off- channel habitat. Habitat availability information is limited to the identification of flows necessary to inundate Old Charley Wash (RK 402), a floodplain wetland on the Ouray National Wildlife Refuge. The objectives of this project were to 1) describe movement and habitat use patterns of adult razorback sucker, 2) describe the growth and survival of immature razorback sucker in wetlands relative to main-channel habitat, and 3) determine flows required to inundate Old Charley Wash. Because of the unrelated nature of the above studies, this report has been organized into separate chapters. Capture data during 16 years (1975,1978-1992) and radio-telemetry data during three successive spawning events (1993-1995) were used to describe seasonal and spawning movements of adult razorback sucker in the middle Green River. Greatest distance traveled by razorback sucker occurred just prior to and shortly after spawning. Movement to spawning sites was associated primarily with discharge, with greatest numbers present on the spawning bar prior to peak flow. Although data suggested that many razorback sucker in the middle Green River spawned at a single location between river kilometers 492 and 501, other spawning sites were also used. Multiple use of spawning sites by several fish suggested a single reproductive population in the middle Green River. Experimental studies to evaluate growth and survival of captive larval and juvenile razorback sucker in wetland habitat provided limited useful information. Growth and survival of juvenile razorback sucker in wetlands, with the exception of Old Charley Wash, tend to be higher than in main channel backwater habitat. An experiment on growth and survival of larval and juvenile razorback sucker in the presence of red shiner Cyprinella lutrensis was unsuccessful because all razorback sucker larvae were consumed by red shiner and only one razorback sucker juvenile survived to the end of the experiment. Predation of larval razorback sucker by adult red shiner suggests the potential for nonnative impacts on the survival of endangered fishes in wetlands. An evaluation of availability of habitat in the spring was limited to defining river flows necessary to connect Old Charley Wash (between 405 m3/s and 455 m3/s) , an 80 ha wetland on the Ouray National Wildlife Refuge, with the Green River. MANAGEMENT IMPLICATIONS Movement of adult razorback sucker to spawning areas was influenced primarily by rising flows of the natural hydrograph. Tag-recapture and telemetry data showed that postspawned fish moved to tributary outlets and the vicinity of the Ouray wetland complex. Thus, timing of spring flows seems to be an important cue for attracting and concentrating spawning adults, and the magnitude of flows may influence postspawning 7