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<br />initial CPE (pass 1) was lower on the second trip; however in the other backwater (RM 90.5), the initial <br />~ CPE was higher on the second trip. <br />At the smallest scale of removal (one-day sampling occasion in one backwater) CPE declined on <br />consecutive removal seine hauls during each trip in the RM 60.3 backwater, but the RM 90.5 backwater <br />~ did not show a consistence decline in CPE. We frequently observed a depletion effect in the first four <br />seine hauls in individual backwaters (Figure 17); however many backwaters did not show a consistent <br />decline indicating depletion, similar to the RM 90.5 backwater. <br /> <br />Comparison with ISMP <br />The ISMP catch rates of Colorado pikeminnow in the lower Colorado River (ISMP reach 1) were <br />~ lower than the long term mean in 1998 and 1999. CPE decreased from 1998 to 1999, but increased from <br />1999 to 2000 (Figure 18). However, catch rates remained within the range of catch rates observed during <br />ISMP sampling from 1986 to 1997. There were no Colorado pikeminnow captures in the upper Colorado <br />~ River (ISMP reach 2) where removal efforts were also conducted from 1999 to 2001 as part of another <br />study (Trammell et al. 2002). <br />No Colorado pikeminnow YOY have been captured during ISMP in reach 2 since 1992. In the <br />Colorado River ISMP (reach 1) catch rates for nonnative cyprinids in 1998 and 1999 were lower than the <br />long term mean; however, catch rates were also very low in 1997. NNC CPE in 2000 was higher than the <br /> <br />long term mean. Thus, the low catch rates of nonnative cyprinids during ISMP in 1998 and 1999 cannot <br />conclusively be attributed to nonnative removal efforts. <br />4.0 DISCUSSION <br />Interpretation of these data is difficult due to the number of confounding factors influencing the <br />abundance and catchability of nonnative cyprinids and native fishes, as well as changes in the sampling <br />regime between years. Nonnative cyprinid species in this study are small bodied, extremely abundant, <br />have high fecundity rates and are able to flourish in a wide variety of habitats range-wide (Lentsch et al. <br />M 1996). Nonnative cyprinids were frequently visually observed in many low-velocity shoreline habitats <br />-14- <br />