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Recaptures vs stocking season For bonytail at large less than six months, no significant difference (p=OA7, t=0.07, df=9) was observed between mean electrofishing RCR offish stocked in the fall (mean RCR=0.42) and the spring (mean RCR=OA7). However, a comparison of growth for fish recaptured prior to their first winter, during 1996-1998, reveals differences between fall and spring stocked fish (Figures 8 and 9). Mean growth rate for spring stocked fish was 6.3 mm (SD=5.8 mm) after 2-9 days at large (n=23) and IDA mm (SD=4.3 mm) 58-70 days after stocking (n=15; Figure 8). The mean growth rate for fall stocked fish was -0.3 mm (SD=3.36 mm) after 2-20 days at large (n=23; Figure 9). Negative growth for fall stocked fish prior to overwintering is likely due to significantly declining water temperature shortly after release (Figure 5). This could indicate too short of an acclimation period prior to overwintering. Obiective 3: Determine movement and the potential for habitat utilization overlap between bony tail and roundtail. Investigate whether Gila species utilize similar micro- and meso- habitats. Habitat Use and Dispersal Habitat use of stocked bonytail juveniles For the 1,186 bonytail recaptured in the Colorado and Green rivers, habitat data for the actual location of capture was recorded for only 314 individuals. Overall, juvenile bonytail were found most frequently (55%) in habitats associated with flooded tributaries (Tables 7-8). Bonytail found in flooded tributary habitats were generally small (mean TL 95 mm), while a few larger individuals (239-220 mm) were captured near the mouths of tributary streams. There was also an overall trend for fish captured in flowing habitats, such as runs, riffles, eddies, and shorelines, to be larger than those found in backwaters and flooded tributaries. Recorded habitat use patterns were different between the Colorado and Green rivers. The most noticeable difference was in habitat use observed for electro fishing returns. On the Colorado River, electrofishing captures were restricted mostly to runs and shoreline habitats (87%). While on the Green River, electrofishing captures occurred in eight different habitat types. In the Green River, the primary habitat of capture for electrofishing was flooded tributaries (52%), while 17% and 25% of captures occurred in backwater and shoreline habitats, respectively (Table 7). The difference in electrofishing returns are likely due to levels of effort and area covered in each river. Electrofishing in the Green River was much more intensive in both time and habitat covered. Habitat use of other Gila species Throughout the duration of this study, a large percentage of humpback or roundtail chubs captured in the Colorado and Green rivers were identified simply as "chub" or "Gila". For this reason, all chubs other than bonytail were combined into the category "other Gila". The most 13