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<br />A fairly strong relationship was found between abundance of native species and
<br />peak annual flow (r = 0.794, P = 0.105), and a somewhat stronger relationship was found
<br />between native abundance and the drift season mean flow (r = 0.876, P=0.051) (Table 5).
<br />Strong correlations between native abundance and flows were due to the very wide
<br />difference between the largest drift estimate (5. 8M), produced in the highest flow year
<br />(1995), and the lowest drift estimate (0.5M), produced during the lowest flow year (1994)
<br />(Table 4).
<br />
<br />Table 4. Catch and drift estimates for total, native, non-native fish and Colorado
<br />pikeminnow for a standardized 26 day period for Lorna, Colorado River
<br />1992-1996.
<br />
<br />SAMPLING PERIOD. 26 Days 1992 1993 1994 1995 1996
<br />Total fish collected 2,307 2,345 2,746 6,188 ' 1,605
<br />Native fish collected 1,636 2,108 1,058 5,729 1,439
<br />Nonnative fish collected 630 235 1,600 355 161
<br />Total fish per cubic meter * 1000 291.1 243.2 142.6 351.9 109.3
<br />Native fish per cubic meter * 1000 206.5 218.6 55.0 325.8 98.0
<br />Nonnative fish per cubic meter * 1000 79.5 24.4 83.1 20.2 11.0
<br />CPM per cubic meter * 1000 6.6 3.6 3.0 12.9 -2.4
<br />Total fish drift estimate per hour 4,120,399 4,031,717 1,070,397 6,180,629 1,660,881
<br />Native fish drift estimate per hour 3,058,942 3,615,536 497,021 5,778,655 1,542,289
<br />Nonnative fish drift estimate per hour 980,752 412,996 540,036 316,200 118,592
<br />CPM drift estimate per hour 105,555 74,781 25,215 267,994 27,642
<br />
<br />No significant relationships were observed between abundance of nonnative
<br />species and the three flow variables even though the two lowest flow years 'produced the
<br />highest number of nonnative larvae (Table 5).
<br />
<br />A highly significant relationship existed between pikeminnow abundance and the
<br />mean drift season flow (r = 0.915, P = 0.021) (Table 5). As was the situation with native
<br />species abundance, there was a large difference between Colorado pikeminnow abundance
<br />for the best (1995, 268K) and the poorest years (1994, 25K). There was also a wide
<br />variation between drift season flows for those two years. The abundance of Colorado
<br />pikeminnow in the drift was poorly correlated to peak and the peak season flows. Poor
<br />correlations resulted because 1992 and 1994 had similar peaks but dissimilar larval
<br />abundance. And also 1996 was a moderate flow year but had low abundance estimates for
<br />both Colorado pikeminnow and native fish larvae (Table 4). In contrast, native drift
<br />estimates were not found to be disproportionately low at other stations in 1996, but
<br />intermediate at the Upper Colorado, Lower Gunnison, and Bridgeport stations (Appendix
<br />1, Tables 1,4, and 6). Non consistent results between stations may suggest that the poor
<br />larval production in 1996 at Lorna results could be an anomaly.
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