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Turbidity was more variable in 1996 because of several late summer storm events. These conditions may be more productive than 1995 and slightly greater mean total length (34.6 mm) was measured. This small difference in total length may not be significant. This may indicate an environmental threshold for increased recruitment was reached in 1994, but not reached in 1996 even though conditions were better than 1995. The results of monitoring efforts were incorporated in Table 2 above and increase the flow year - YOY chub cohort comparisons by two years (1992 and 1993). Unfortunately, increasing the sample size from 3 to 5 did not increase our ability to statistically predict reproductive success based on flows. It is apparent that chubs in Deso/Gray reproduced successfully over a wide range of flows. Growth of YOY and time of spawn were also reported as result of the monitoring efforts; 1.992-1996. Prior to the nursery habitat study the opportunity arose for some ancillary YOY sampling in 1992 (9-14 September) and 1993 (12-15 July), which provided a second look at those year's YOY chub cohorts. Low velocity habitat sampling in September 1992 revealed one YOY chub (trip CPE = 0.0017) which corroborated the findings of low Gila spp. reproduction determined earlier that year (during the July monitoring trip). In July 1993, 26 YOY chubs (avg TL = 18.9 mm) were collected which was the first indication of the stronger year class detected in the monitoring effort later that year. A length frequency comparison of the two collections of the 1.993 Age-0 cohort provided a basis for an analysis of YOY chub growth rates and hatching times (Report C: Figure 5). The July 1993 distribution of Age 0 chub lengths reveals a single modal peak at 19 mrn TL. Days post-Batch were back calculated first by converting total. length to standard length (Chart and Lentsch 1998b) and then applying formula developed by Muth (1990). Results of this analysis indicated the majority of chubs collected 12-15 July 1993 hatched on June 21 and were spawned June 16 (back calculated dates offer only an approximation of life history events). Green River flows were 14,000 cfs and 16,700 cfs on the estimated spawn and hatch dates, respectively. The length frequency analysis of the August 1993 catch reveals a more scattered bi-modal distribution of Age-0 chubs. The first peak occurs at 30 mm TL. Applying the methodology described above we back calculate a hatch date of July 13 and spawn date of July 8 for this younger contingent of chubs collected in August 1993. The second peak at 46 mm TL is much less discrete. These fish were too large to back calculate hatching dates, but were presumed to be the group of fish sampled earlier in July. Based on this assumption, Age 0 chubs grew, on average, at a rate of 0.36 mm/day from mid July to late August. Green River flows averaged 2,924 cfs, and river temperatures averaged 24.5 C during that growth period. Chub CPUE was positively correlated with CPUE'for five other species. These correlations were weak, but statistically significant (Colorado pikeminnow, r-2=0.008; bluehead sucker, rz=0.04; red shiner, r2=0.02; fathead minnow, ~=0.05; and sand shiner, rZ=0.006). Because this study was predicated on the previous findings of the importance of backwater habitats to YOY chubs, no attempt was made to sample other habitat types. Therefore, it is not possible to address the question of use of habitats having measurable flow. The characteristics of backwaters used by YOY chubs can be described. Mean depth of backwaters used by chubs was 0.59 m, almost exactly that reported by Valdez and Clemmer (1982). Mean depth of backwaters used by chubs was 0.09 m greater than that for habitats not used by YOY chubs. ~..., ~. ,. --, __ xii