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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Duchesne River Adult fish monitoring during the peak flow period and pre-ice period in 1999, and the post-ice period in March 21-24, 2000 were made for the sole purpose of monitoring the presence of Colorado pikeminnow(i.e., fish composition not recorded). Pre-ice and post-ice sampling was conducted to corroborate telemetry observations that pikeminnow tended to leave the Duchesne River during the winter period. The dates of adult sampling and gear types used are given in Table 1, and the corresponding flows occurring at the time of sampling are given in Figure 2. All native fish were weighed and measured; all nonnative fish were counted and a subsamp1e (usually >50%) was weighed and measured. Radio Telemetry During 1997 and 1998,40 Mhz transmitters manufactured by Custom TelemetryTM were implanted in fish. All transmitters implanted in 1997 and 1998 had a battery life of 24 months. Due to difficulty in finding 40-Mhz transmitters, 149-Mhz transmitters manufactured by LOTEK™ were implanted in fish in 1999. The battery life of transmitters implanted in 1999 ranged from 324 to 824 d. The smaller transmitters were used in smaller fish. All transmitters were surgically implanted into the body cavity of fish using standard procedures. Transmitter antennas were placed inside the body cavity in an effort to reduce the mortality risk to fish. Fish were released as close as possible to the sites they were captured. Colorado pikeminnow implanted with transmitters were captured by electroshocking during fish composition sampling and additional collections made specifically to capture pikeminnow (Table I). Aerial flights to locate implanted fish were conducted approximately monthly during the spring and fall in 1997 (Table 2). Thirty-three flights were completed between June 1997 and September 2000. Most flights monitored the Duchesne River between the confluence of the Green River and Myton (rmi 33.3), and the Green River between Split Mountain Canyon (rmi 319) and Three Fords Rapid (rmi 251) in Desolation Canyon. In addition to aerial flights, ground monitoring trips were conducted at approximately 2-wk intervals through the spring and summer months. Two fish telemetry monitoring stations were installed near the Duchesne River to monitor movement of radio tagged fish. Both logging stations consisted ofLOTEKn-l radio loggers model SRX 400. The Ouray station was installed at rmi 1.8 in August 1997, and the Randlett station at 3