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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Duchesne River Adult fish monitoring composition and 14 during trips devoted only to collecting pikeminnow for transmitter implantation) and four razorback sucker were captured (1 during adult sampling between 1997- 1999, and 3 during transmitter implantation collections). A shortage of available PIT tag scanners prevented field staff from determining whether Colorado pikeminnow collected were recaptured. The species composition and total catch data for each year is summarized in Appendix Tables 1,2,and 3. While carp were found distributed among all reaches, white sucker, mountain whitefish, brown trout and flannelmouth sucker were collected more often in the upper reach during the spring than the lower reaches (Table 3). Although Colorado pikeminnow were captured throughout all reaches, more pikeminnow were captured in the middle and lowest reaches of the study area during fish composition collections (Table 3). A greater total number of Colorado pikeminnow were captured in the lower reach, however, many of these fish were collected during supplemental sampling efforts in the lower reach to capture fish for transmitter implantation. During both 1997 and 1998, catch rates of Colorado Pikeminnow were highest in mid-June (Figure 3). The only razorback suckers collected were found in the lowest reach during spring, close to the confluence with the Green River. In addition to the single razorback sucker collected in the fish composition samples, three additional razorback sucker and one razorback sucker x flannelmouth sucker hybrid were collected near the confluence ofthe Green River on 10 June 1999 while attempting to capture Colorado pikeminnow for transmitter implantation. Of the additional three razorback sucker, two were identified as fish produced and stocked from the Ouray National Fish Hatchery. We did not collect any pikeminnow in the Duchesne River just prior to ice formation in 1997, but a single Colorado pikeminnow (406 mm TL) was captured 0.2 rmi below the Myton Bridge on 15 November 1999. Eight Colorado pikeminnow were collected after ice-out 21-24 March 2000, one near Randlett (rmi 14.6) and seven below the pipeline (rmi 6.7). During base flow fish collections, more fish were captured in the upper reach ofthe study area. In addition, some species, including bluegill, green sunfish, fathead minnow, speckled dace, red shiner and redside shiner, were more numerous in summer baseflow collections in 1997 than in the spring electro fishing collections (Appendix Tables 1 and 2). Differences in the the abundance ofthe small bodied fishes may be due to sampling gear (i.e., fathead minnows and red shiners cannot be captured effectively with the larger mesh nets used during e1ectrofishing). 5