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a <br />162 UTAH ACADEMY PROCEEDINGS, VOL. 45, PART 1, 1968 <br />from the winter generation. Collecting trips were made from <br />the dam to Taylor Flat on August 19 and October 14, 1967, and <br />no summer-generation nymphs were found within 9.5 km of the <br />dam (Figure 2). Ninety percent of the Baetis nymphs in samples <br />2000 <br />\ AUG 19 <br />1967 <br />a <br />Z Iooo OCT 14 <br />a <br />W 0 ®, <br />Q O 5 10 15 20 25 30 <br />co KILOMETERS BELOW FLAMING GORGE DAM <br />FIGURE 2. Longitudinal distribution of Baetis nymphs in the Green River <br />between Flaming Gorge Dam and Taylor Flat, on two dates in 1967. The <br />circles represent the age distribution of nymphs. The percentage of nearly <br />mature numphs is represented by the solid portion of the circle, the immature <br />nymphs (<4.5 mm body length) by the open portion. <br />at Little Hole on October 14 were newly hatched. The highest <br />standing crop of Baetis nymphs (1,850/m2) was found 6 km below <br />Little Hole (13 KBD), but numbers were substantially lower than <br />was observed at Little Hole in 1965. <br />Drift-net catches reflected this reduction in Baetis populations. <br />The mean 24-hr catch of Baetis nymphs at Little Hole in 1967 was <br />11/28m3, whereas this catch was 3,161/28m3 in 1965. The mean <br />24-hr catch of Simuliidae decreased from 340/28m3 in 1965 to <br />9/28m3 in 1967. <br />G, <br />?M <br />m <br />T <br />COMPARISON OF PRE-AND POSTIMPOUNDMENT <br />MACROINVERTEBRATE FAUNAS <br />Information from several sources was used to compare the <br />invertebrate fauna of the study area in 1964-65 with preimpound- <br />ment fauna. Data on invertebrate forms present in the Green <br />1 <br />t <br />1 <br />t <br />a <br />a <br />r