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hauls were taken in the backwater. Effort was recorded as azea swept by the seine. Colorado squawfish were measured, counted, and released alive if they were large enough to be reliably identified. Fish of other species that were also large enough to reliably identify were counted and released. All remaining fish in the first sample were preserved for later identification in the laboratory to check for Colorado squawfish too small to be identified in the field. Non-target fishes were later counted in the laboratory for this sample only. Investigators then proceeded downstream to the next backwater which was also sampled with two non~verlapping seine hauls. Colorado squawfish were measured, counted, and released alive. No other fish from the second backwater were preserved or counted for ISMP. However, a second study evaluating the abundance of introduced species in conjunction with ISMP counts or preserves all specimens collected from all backwaters in the Colorado River. These data will be reported elsewhere. After sampling the second backwater, investigators proceeded downstream to the top of the next 5-mile reach before sampling again. Samples were not taken within a 5-mile subreach if no backwaters meeting ISMP's criteria were found. The first backwater sampled in each 5-mile subreach was considered a primary backwater, and the second backwater sampled was considered a secondazy backwater. Although there were some differences in how nonendangered fish were handled in primary and secondary backwaters, there was no difference in sampling technique. Therefore, catch rates for YOY Colorado squawfish were calculated using combined data from both primary and secondary backwaters. The relative density, or catch per effort (CPE), of YOY Colorado squawfish was determined by the number collected per area of backwater swept with the seine. Because of the relatively low number of Colorado squawfish collected every year, data are not normally distributed-an assumption required by many data-analysis techniques. McAda (1989a) investigated several methods of data analysis for the monitoring program and suggested using geometric-mean CPE rather than the more standazd calculation of azithmetic mean. The geometric mean is calculated by using a log transformation (log~(CPE+1)) before calculating the mean. The mean of the log values is then transformed back to a standard value ((2.71828m°°)-1). A log transformation improves the normality of CPE data, but unfortunately, low catch rates still result in non-normal data in some instances. Change in CPE over time should reflect change in the number of YOY Colorado squawfish present each fall. Geometric-mean CPE was calculated using each backwater as the basic element rather than each seine haul. The total number of Colorado squawfish collected in both seine hauls in a backwater was divided by the total area seined with both seine hauls to determine CPE for that backwater. Geometric-mean CPE was then calculated for each monitoring reach and for 10-mile intervals within monitoring reaches. To save space, geometric-mean CPE will be referred to as gmean CPE throughout the remainder of this report. Gmean CPE, calculated by 10-mile subreach, was plotted in histograms to compare general distribution patterns among reaches and years. Gmean CPE for the entire reach was plotted to compare changes over the 8 years of ISMP. Length-frequency distributions were developed by reach for all Colorado squawfish collected. Mean total length and other summary statistics were developed for the four reaches sampled. Number of all species collected was totaled for the first seine haul in primary backwaters. Gmean CPE was calculated for the three most common species in these collections. 3