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<br />5-8 <br /> <br />taken at about 2-hour intervals indicate that the drift densities are <br />related to time of day (Figure 5). Details on the time periods, sample <br />size, mean densities, and standard deviations are presented in Table B-8. <br />Drift densities were highest between midnight and 4 am (0.6545 <br />fish/lOOO cubic feet) and between 8 pm and midnight (0.5963). About 60~ of <br />the drift was recorded during these two time periods. The number of <br />drifting fishes between 4 am and 4 pm was relatively consistent, varying <br />between 0.2304 and 0.2594. The lowest drift density was observed between 4 <br />pm and 8 pm. <br />An analysis of variance revealed a significant difference (P=.Ol) <br />between the hourly means. By using Fisher's least significant difference <br />procedure for multiple comparisons, it was determined that there were <br />significant differences between the two maximum values and the four minima. <br />This indicates that drift densities at the JH-1 site can be expected to vary <br />with the time of day, and that the highest densities can be expected between <br />8 pm and 4 am. <br />Peaks in drift density were found by Valdez and Carter (1983) during <br />the same time period the previous year about 35 river miles upstream, <br />although the difference in means was not significant (P=.Ol). The lack in <br />significance is attributed to the pooling of samples collected over a 3- <br />month period which caused high seasonal variation in densities and thus, <br />high diel variation. Similar analyses conducted in this study also failed <br />to show significant differences in mean diel drift densities because of the <br />high variation in numbers seen during the study. The 24-hour sample effort <br />to assess diel drift was designed to sample drift over a short time period <br />and reduce the variation of seasonal densities. <br />