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Table 2. - Summary of survival of young Colorado squawfish marked with syringe injected elastomer and held overnight (18-19 h) in enclosures in the Green River. Location Number Date Survival marked survive (%) (RK) Mark 20 Apr 94 464.2 rt dors, ant 20 19 95 5 Oct 94 63.6 It dors, ant 34 34 100 23 Mar 95 64.4 rt dors, ant 22 19 863 25 Mar 95 64.3 rt dors, pos 8 8 100 11 Oct 95 55.2 It dors, pos 10 1 lOb 20 Apr 96 50.2 rt dors, pos 9 6 67 22 Apr 96 50.2 rt dors, pos 5 5 100 108 92 85c 3Dead fish were smaller than survivors and had marks on their abdomens; cause of death was probably due to entanglement in enclosure mesh. bHandling conditions seemed good; afternoon wind may have caused turbulence that resulted in sedimentation of enclosure and mortality c mean calculated as (92 /108) * 100 summer 1994 was surprisingly high. The distribution of total lengths for fish captured in the Canyonlands reach that year was bimodal with modes at 47 and 67 mm (Figure 5). Analysis of drift collections from the Green River near Green River, Utah, showed that emergence of larval Colorado squawfish also had a bimodal distribution for summer 1994 (K. R. Bestgen, pers. comm.). Emergence periods were concentrated around 28 June and 25 July. To confirm that age-O Colorado squawfish can attain the observed sizes in their first season, a growth analysis was conducted. The analysis simulated growth of age-O Colorado squawfish using (1) estimated fertilization date based on emergence periods (15 June), (2) a temperature-dependent growth equation (Bestgen 1996; Bestgen et al. 1997), (3) the temperature regime for the Green River near Green River based on u.S. Geological Survey records for summer 1994, (4) an average daily growth rate of 0.5-mm TL/d which is a common growth rate in wild Colorado squawfish (Bestgen 1996), and (5) day of capture for marking as the end of the growth period. Results of 13