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Late Juveniles and Adults ^ The late juvenile /adult component of the Westwater Canyon fish community is comprised primarily of native chubs. ^ Catch rates of humpback chub fluctuated around the following site mean CPEs (fish / 23 m net hour): Miner's Cabin = 0.4, Cougar Bar = 0.47, and Hades Bar = 0.32. The trend throughout the study was stable, but variable. These catch rates represent some of the highest catch rates for humpback chub in the upper basin and rival those in the Grand Canyon near the Little Colorado River. ^ Catch rates of roundtail chub also varied greatly between trips, but trended downward, _ particularly in light ofpre-project data. ^ Recaptures of PIT tagged chubs indicated that both the humpback and the roundtail chub moved little - 82.8% of the humpback chub recaptures and 92% of the roundtail chub recaptures indicated no net movement. A roundtail chub did move the greatest distance (4.1 miles). Humpback chub persist longer in the canyon (either live longer or remain in the canyon longer). ^ Lincoln-Peterson population estimates were calculated whenever possible. Humpback chub population size was estimated at 1050 individuals between RMs 121.5 and 121.1 in 1996. Roundtail chub population estimates ranged from N=1760 in 1993 at the Miner's Cabin site to N=721 at the same site in 1996. Although all the estimates were associated with large confidence intervals, the overall trend was similar to the trend in CPE. ^ Sympatric species, including channel catfish, represented a relatively insignificant portion of the main channel and shoreline catch. Our feeling is that habitat availability, particularly during the peak flows, is certainly not preferred by juvenile channel catfish and likely precludes this species from gaining a foothold in Westwater Canyon. This and the lower densities ofnon-native cyprinids in canyon low velocity habitats likely explain why Westwater Canyon supports a stronger population of native chubs than other areas. Channel catfish catch rates were greatest in 1992 and were reduced during the high flow years of 1993 and 1995. Nonnative control maybe the mechanism by which high flows benefit chub reproductive success. RECOMMENDATTONS ^ YOY chub densities were greatest in Westwater Canyon in 1996 when flows peaked near 30,000 cfs at the Stateline gage. We would recommend trying to achieve a peak magnitude of 30,000 cfs as many years as possible. ^ Flows in excess of 40,000 did not appear to have an immediate positive affect on chub reproduction but did negatively impact nonnatives. There was also an apparent beneficial antecedent effect of high flows. YOY chub densities were high in 1994 and 1996 following the relatively high flows of 1993 and 1995. Historically (1914-1962), an annual peak flow of 40,000 cfs (as recorded at the near Cisco, Utah, gage) was exceeded 57% of the time. Based on the results of this study, we recommend a flow in excess of 40,000 one in three years to benefit humpback chub and the entire fish community in Westwater Canyon. 30