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1996 year class or older (age-2+). The large numbers of Colorado pikeminnow captured in 1999 were primarily of the 1998 year class (age-1 ); ranging from 30 to 80 mm TL. In 2000, the Colorado , pikeminnow were primarily of the 1999 year-class (age-1 ), although several age-2+ fish (140-200 mm TL) were also captured (Figure 3). Total captures of fish were similar among years {Table 2). Effort in area seined was similar ~ between 1998 and 1999, with a 48% increase between 1999 and 2000 (Table 3). From 1998 to 2000, 139,713 fish were removed. Nonnative cyprinids comprised the overwhelming majority (91 %, 125,904) of all fish captured. An additional 27,917 fish were captured in control habitats and released. Of those, ~ 93.4% (26,344) were nonnative cyprinids (Table 2, Figure 4). Nonnative cyprinids were grouped into one category (NNC) for processing so individual percent compositions are unavailable for red shiner, sand shiner and fathead minnow. No other nonnative species comprised more than 1 % of the total catch in ~ any single year. Captures and percentages of nonnative fish in treatment reaches were similar among years, with the fewest fish captured in 1998, and the most in 1999; in control reaches, captures were similar between 1998 and 2000, while double the numbers were captured in 1999. In treatment samples, ~ native fish collectively comprised 12.2% of the total in 1998, 5.7% in 1999, and 8.6% in 2000 (Figure 4). Unidentified sucker larvae were the largest component in 1998; these fish were likely primarily native species. Colorado pikeminnow juveniles comprised 0.2% of the total in 1998, 2.6% in 1999, and 1.3% in , 2000. No razorback sucker larvae or juveniles were identified during the project. Little change was observed in the composition of native and nonnative fishes among years, and little difference was observed between treatment and control reaches although the percentage of nonnative fishes was higher in the control reach (Figure 4). Changes in age structure of nonnative cyprinids (subadults/adults) were observed between trips each year. The numbers and relative abundance of subadults (<40 mm TL) tended to increase during the S year primarily due to reproduction (Figure 5). The relative abundance of subadult nonnative cyprinids likely was underestimated because seine mesh size was selected to exclude fish less than 25 mm. Although this assumption was not specifically evaluated, small fish were frequently observed to escape through the seine. However, sucker larvae greater than 20 mm were often captured. In 1998 and 1999, ~ -9- 1