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of YOY chubs within Westwater Canyon was nearly as high, .673, recorded during the summer of 1996. The catch rates of chubs were significantly higher in the above- canyon and canyon sub- reaches than in the sub-reach below the canyon. Reproductive success as measured by densities of YOY chubs was positively correlated with the previous year's peak flow, and negatively correlated with the amount the June monthly mean flow deviated from the historic monthly mean. The geatest canyon catch rates occurring when the river peaked near 30,000 cfs as it did in 1996. A chi square analysis indicated YOY chubs used backwater habitats as they were available, but did not select for them. Similar use was recorded ~in embayments and shoreline habitats within Westwater Canyon. Habitat availability within Westwater Canyon was not dependent on the spring peak as much as instantaneous flow. Nursery habitat were basically any low velocity area, whether that be a typical secondary channel backwater or merely a sculpted area in the shoreline bedrock (referred to as embayments). Much of the available habitat within Westwater Canyon was not formed by sediment deposition as the classic Colorado squawfish nursery areas are. Non- native species were found in lower densities in Westwater Canyon than above or below the canyon - again a function of canyon habitat availability. Non-native densities wexe negatively correlated with the peak flow at the State Line gage. The analysis of chub recruitment was basically a comparison of cohort (as determined by length frequency analysis) densities (electrofishing CPE) relative from year to year. From this analysis it appeared the 1994 cohort recnrited the best; the 1993 cohort the worst. Several biological and environmental variables (year class strength, size offish by fall, non-native densities in the fall, winter flows and the cohorts first flood (spring peak subsequent to hatch) were considered in descn~ing these observations. . The humpback chub population in Vyestwater Canyon was monitored at three sites established for the Interagency Standardized Monitflring Program (ISMP): Mmer's Cabin (RM 124.3 - 124.1), Cougar Bar (RM 121.5 -121.1), and Hades bar (RM 120.1 -119.9). Densities of adult humpback chub, as referenced by trammel net CPE (fish / 23m net hour), fluctuated greatly from trip to trip but overall remained fairly stable -with the trend in CPE slightly up at Mrner's Cabin and slightly down at the other two. The same data for roundtail chub indicated a relatively strong downward tend at all sites. Lincoln Peterson population estimates, although compromised by large 95% confidence intervals, showed a similar trend in population size for the two speaes. DRAFT , . ii