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RESULTS <br />Relative Abundance <br />Catch rates of humpback chub declined markedly in 2000 compared with 1998 and 1999. <br />A total of 184 individual humpback chubs were handled in 1998 (does not include within year <br />recaptures), 293 in 1999 (four sampling trips compared with three trips in other years) and 68 <br />in 2000. Mean CPE ranged between 0.3 and 0.55 humpback chub per net hour in 1998 and <br />1999, but did not exceed 0.2 fish per hour in 2000 (Figure 2). Mean CPE increased slightly as <br />sampling progressed through fall 2000, but the increase was not significant. Mean CPE was <br />not significantly different among rotations in 1998 and 1999, but mean CPE for all rotations <br />in 2000 were significantly different (P<0.05) than all rotations in 1998 and 1999. Mean CPE <br />of roundtail chub also declined in 2000 when compared with the first two years, but the <br />decrease was not as great as observed for humpback chub (Figure 3). <br />i <br />0.8 <br />N <br />._ <br />0.6 <br />W <br />v 0.4 <br />~ 0.2 <br />0 <br />- - --- --- <br />---- --- <br />$'--8- -8- -B- $-- --- --- <br />------------------ -------- <br />1 2 3 1 2 3 4 1 2 3 <br />1998 ~ 1999 ~ 2000 <br />Year and Sampling Ro#a#ion <br />FIGURE 2.-Mean CPE (fish per net hour; bars represent ± 1 SE) of humpback chub <br />in Black Rocks, 1998-2000. <br />5 <br />