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.-~ <br />'` 2 <br />1.5 <br />~ 1 <br />U <br />~ 0.5 <br />c~ <br />a~ <br />~ 0 <br />--- ------------------------------------------------- <br />$ i' $ "~-s... <br /> <br />Year and Sampling Rotation <br />FIGURE 5.-Mean CPE (fish per net hour; bars represent ± 1 SE) of humpback chub <br />in Black Rocks during Interagency Standardized Monitoring sampling (1988-1997) and <br />during the current study, 1998-2000. The regression was significant and the slope of the <br />line through the annual means was significantly different than 0 (P<0.05). <br />trend over the 12-year sampling period. Mean CPE exhibited significant differences among <br />years (P<0.05)`and the slope of regression line through the annual means was significantly <br />different than zero (P<0.05). Mean CPE was lower in 1998-2000 than during previous <br />sampling periods. <br />Size Structure -The size range of humpback chub within Black Rocks remained <br />consistent during the 12 years of sampling, but shifts in size structure occurred (Figures 4 and <br />6). The greatest difference was in 1991 when 86% of all fish collected were z 30 cm TL. A <br />bimodal distribution first appeared in 1994 and was maintained through the current study. In <br />general, a higher percentage of fish collected during ISMP were greater than 30 cm TL than in <br />the current study (1988-1997 - mean, 70%; 1998-2000 -mean, 55%). However, small <br />fish were present in all years which suggested that recruitment was occurring at some level <br />throughout the sampling period. <br />10 <br />