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CPE over time should reflect change in the number of YOY Colorado squawfish present each fall. Change in CPE is often used to estimate change in fish populations (e.g. Ricker 1975; Ney 1993). Samples identified in the laboratory were used to develop a correction factor (Table 1) to compensate for Colorado squawfish that might have been too small to identify in the field, and thus were not counted. This correction factor was based on the ratio of Colorado squawfish found in preserved samples to those identified in the field. The number of Colorado squawfish found in unpreserved samples was multiplied by this number before CPE was calculated. Geometric-mean CPE was calculated using each backwater as the basic element rather than each seine haul. The corrected total number of Colorado squawfish collected in both seine hauls in a backwater was divided by the total azea 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. A second index of relative abundance was calculated by totaling the number of Colorado squawfish collected within each 10-mile interval and dividing that number by the total azea seined within that same interval. This index will be referred to as total CPE in the rest of this report. Valdez and Cowdell (1992) also considered gmean CPE and total CPE to be appropriate methods of calculating CPE. Gmean CPE and total CPE were plotted as histograms to compaze the two values among years and reaches. Gmean CPE, calculated by 10-mile subreach, was plotted in histograms to compaze general distribution patterns among reaches and yeazs. Gmean CPE for the entire reach was plotted to compaze changes over the 7 yeazs of ISMP. Number of all species collected was totaled for the first seine haul in primazy backwaters. Gmean CPE was calculated for the three most common species in these collections. CPE for YOY Colorado squawfish in these seine hauls was correlated with CPE_of the three most common species to evaluate any effect of abundance of one species on another. Table 1.-Correction factor used to adjust total number of Colorado squawfish in samples that were not preserved and percent increase in total fish collected used in CPE calculations (Calculations aze summazized in Table B-1). 1986 1987 1988 1989 1990 1991 1992 Reach COR` PCIb COR PCT COR PCT COR PCT COR PCT COR PCT COR PCT 1.033 1.2 1.000 0.0 1.200 14.7 1.004 0.0 1.109 2.7 1.087 0.0 1.074 0.1 1.429 0.0 1.150 0.0 1.000 0.0 1.045 0.0 1.042 0.0 1.000 0.0 1.000 0.0 1.024 2.0 1.000 0.0 1.000 0.0 1.001 0.0 1.000 0.0 1.000 0.0 1.000 0.0 4 1.106 8.5 1.008 0.1 1.111 8.2 1.024 1.8 1.047 3.6 1.002 0.0 1.039 2.8 °Correction factor used to compensate for Colorado squawfish that were not identified in the field. Only used for seine hauls when no fish were preserved for later identification. "Percent increase in number of Colorado squawfish used in CPE calculations resulting from use of correction factor.