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habitats were available immediately after peak flows. Trammell and Chart (1999d) found that spawning and drift periods of Colorado pikeminnow ranged from early June to late August in the Colorado River in , Utah. Thus, removal efforts conducted in Juiy and August likely overlapped spawning and drift periods, particularly in 2000. Discharge usually fluctuated throughout the study period each year. Consequently, habitats sampled were smaller and shallower than on the Green River, and were much more ephemeral. ! Peak flows for the Colorado River as measured at the USGS Colorado River at Cisco gage (#09180500) were 28,500 in 1998 (moderately dry), 19,000 in 1999 (dry) and 17,500 in 2000 (dry). Discharges during the sampling period for all three years were below 12,000 cfs. Sampling flows in 1998 and 1999 (4000- ~ 12000 cfs) were distinctly higher than in 2000 when flows were consistently below 4,000 cfs (Figure 2b). Control sites were below and between the treatment areas. Due to their ephemeral nature, control sites on the Colorado River changed during each year. Methods of sampling on the Colorado River differed slightly from those on the Green River and were also altered during the study. In 1998, the intensive block and seine technique was used only on the first two removal trips. The habitats were generally much smaller than on the Green River and seines ~ could be easily pulled over the entire habitat area; therefore, for the remaining trips in 1998, and all trips in 1999 and 2000, three complete seine hauls were made in each habitat (three removal passes). In all years, at least one control habitat was sampled above or below each of the three study reaches. No ~ exclusionary block nets were used in the Colorado River. 2.3 Data Analysis Effort was calculated as area seined. The data are presented as total fish removed and as CPE (fish/10m2). Only the first removal seine haul (if the entire backwater was seined in one haul) or the mean of the first seine haul in each cell of the backwater on each sampling occasion was used for CPE analysis 1 because the ongoing removal artificially lowers the apparent CPE. To detect statistical differences in relative abundance, log transformed CPE data were analyzed using ANCOVA among years and between control and treatment areas. Sampling trips were treated as covariates in this analysis to control for effects of cumulative fish removal but not to assess effects of removal per se. Analysis of effects of ~ -7- 1