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<br />20 <br /> <br /> <br />Y = 0.451 + 0.373 X <br />r squ = 0.950 <br /> <br />P = <0.001 <br /> <br /> <br />~ 15 <br />D- <br />O <br />(!) 10 <br />z <br />it <br />n.. <br />tJ) 5 <br /> <br />. <br /> <br />o <br />o <br /> <br />10 <br /> <br />20 30 <br />FALL CPUE <br /> <br />40 <br /> <br />50 <br /> <br />Figure 5. <br /> <br />Relationship of fall CPUE and spring CPUE of Colorado pikeminnow in Reach 3. <br /> <br />Reach 4 <br /> <br />Overwinter survival index of age-O Colorado pikeminnow in Reach 4 ranged from 29% to <br />96% for the five cohorts assessed (i.e., 1989-93), based on changes in geometric mean CPUE (Table <br />4). Decreases in CPUE were significant (Students '1', P>0.05) for four of the five cohorts. Decrease <br />in CPUE for the 1989 cohort was not significant, with a small change in fall to spring density. <br /> <br />Mean total lengths of age-O in fall and spring were similar and consistent for the first five <br />cohorts assessed (i.e., 1987-93) with ranges of34-40 rom and 40-49 rom TL, respectively (Table 4). <br />Increases in mean total length (i.e., average overwinter growth) from fall to spring for the 1989-93 <br />cohorts ranged from 2 mm to 8 mm. <br /> <br />Backwater Depth <br /> <br />Percentage decrease in pooled geometric mean CPUE was found to be highest in shallow <br />backwaters and lowest in deep backwaters in Reach 3 (Table 5). Decrease in mean CPUE for <br />backwaters> 120 cm deep was the lowest and significantly different from all other means (Students <br />of. P<O.05). Decrease in pooled geometric mean CPUE was greatest and significantly different <br />(Students 't', P<0.05) for backwaters <30 cm deep (82%), while decreases in mean CPUE for <br />backwaters 30-60 cm deep (56%), 60-90 cm deep (42%), and 90-120 cm (50%) were lower but not <br />significantly different from each other (Students '1', P<O.05). The relationship of backwater depth <br />to overwinter survival index was positively and significantly correlated (r=O. 744, P=0.0417) (Figure <br />6). <br /> <br />13 <br />