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r introduction and establishment of over 30 species of nonnative fishes has altered the ichthyofaunal assemblage (Tyus et al. 1982). In spite of these changes, the study area supports the largest known population of razorback sucker occupying natural riverine habitat (Modde et al. 1996). Experiments on growth and survival of immature fish were conducted in wetlands and backwaters on the Ouray National Wildlife Refuge (ONWR). Sheppard and Leota Bottoms and Old Charley Wash are natural class IV wetlands (Cowardin et al. 1979) adjacent to the Green River channel between river kilometers 402 and 418 (Figure 2). Artificial dikes have been constructed around each wetland to maintain water during the low flow period in the summer. Water from the Green River was delivered to wetlands by gravity flow, pumping, or, as in the case of Old Charley Wash (Woods Bottom), over- dike flooding. CHAPTER ONE: Distribution and movement of adult razorback sucker METHODS Distribution and movement of adult and subadult razorback sucker were evaluated by two methods: 1) review of the Colorado River Fish Project (U.S. Fish and Wildlife Service, Vernal, Utah), and Recovery Implementation Program Standardized Monitoring Program razorback sucker capture database to determine fish locations and habitat-use patterns in 1975-1992 (specific collections in 1991 and 1992 were made at tributary mouths at weekly intervals), and 2) use of radio telemetry to determine patterns of fish movement during the spring. All CRFP capture data for razorback sucker during April-June were compiled and examined by river kilometer to determine fish locations before, during and after spawning in 1975-1992. Distances moved were measured upstream from the confluence of the Green and the Colorado River. Fish found in tributaries (e.g. Duchesne and Yampa rivers and Ashley Creek) were referenced to the river kilometer at the mouth of each tributary on the Green River. Between 30 April and 11 May, 1993, seven male razorback sucker were collected from suspected spawning locations and implanted with 24-month (25 g) internal antenna radio transmitters (manufactured by AVM). Five fish were collected from the Escalante spawning area (adjacent to Escalante Ranch, RK 492-501, the upper reach of which has been referred to as the Jensen site by Tyus 1987), one from the Yampa River spawning site (RK 0.3 on the Yampa River), and one from the lower reach of Island Park in the Green River (RK 531.6). All fish were positively identified as males by either expression of milt or heavy tuberculation ofthe anal and caudal fins. The fish ranged from 464 to 520 mm in total length and weighed between 1,120 and 1,600 g. Transmitters were surgically implanted into the abdominal cavity and fish were released into the river within 10 to 20 minutes after surgery. During the spring, summer, and fall of 1993, fish were located with radio receivers at approximately 11