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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Duchesne River Adult fzsh monitoring Among fish implanted in the spring of 1997, all but one pikeminnow left the Duchesne River between 19 June and 1 July 1997. The remaining fish (40.323) did not leave the Duchesne River 23 September 1997. Of interest is that fish 40.303 left the Duchesne River on 1 July 1997 and returned 5 August 1997. The same fish was found at rmi 248 on 1 July in the Green River (confluence of the Duchesne) and at rmi 252 on July 22, but was not found during two aerial surveys on 1-3 and 9 July. The single razorback sucker implanted left the Duchesne River and was located in the Green River at rmi 218 on 19 June and rmi 251 on June 25. After 25 June, the single razorback sucker was not located unti122 July in the Green River at rmi 243, after 8 August the transmitter was located on several dates at rmi 221, and we believe the fish either died or evacuated its transmitter. In 1998, four of five pikeminnow implanted the previous year returned to the Duchesne River between the third week of March and mid-April. The only pikeminnow that did not return to the Duchesne River was found in the vicinity ofrmi 226-229 during the summer and fall of 1997, but was never located again in aerial surveys. Three pikeminnow that returned to the Duchesne River in 1998 left the river on June 5 (40.323), June 28 (40.303) and July 1 (40.393) and returned prior to August 8. Fish 40.393 was located in the Green River (rmi 248) on 19 August 1998. Among the five fish implanted in 1997, two (40.374 and 40.323) were recorded entering the Duchesne River on 5 and 27 March 1999, respectively. The transmitters implanted in 1997 were due to expire in the spring of 1999; therefore, the transmitters were probably not functioning when the fish left the river. In 1998, six Colorado pikeminnow were implanted with radio transmitters. Of these six fish, only three were located after implantation (40.422, 40.182, and 40.802). The three fish detected were implanted with radios between 15 April and 4 June 1998, and all three fish left the Duchesne River between 13 and 16 June. None of the fish implanted in 1998 were located in the Duchesne River after 16 June 1998. Although 40.422 and 40.182 were located in the Green River in February, March and May of 1999. Among the 16 Colorado pikeminnow implanted with transmitters in 1999, the logger only recorded 10 leaving the Duchesne River. Three transmitters (codes 15, 19, and 2) were located consistently at the same location and probably represented either transmitters that were lost or fish mortalities. Among the 10 fish recorded leaving the Duchesne River, emigration occurred between 1 June and 10 October, with most leaving between June and August (Table 5). Due to a 7