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All Colorado squawfish that were large enough to reliably identify in the field were measured in total length, counted and released alive. In the first sample in a 5-mi reach all specimens were identified and counted, specimens too small to reliably identify in the field were preserved and subsequently identified in the laboratory. The remaining samples in the Green River were field searched for Colorado squawfish only. The remaining samples in the Colorado River were preserved after releasing all Colorado squawfish that could be reliably identified. These samples were then searched for small Colorado squawfish in the laboratory. Complete information on the sampling design and the details of physical and biological data collection at each sample site are~~presented in the ISMP Handbook. Results Mean catch rates (number of Colorado squawfish collected per 100 m2 seined) were lowest in the upper Colorado River and highest in the lower Green River (Table 6). Catch rates for primary and secondary backwaters were similar within reaches 1 and 2, but were considerably different in reaches 3 and 4. In contrast with Table 6. Mean catch-per-unit-effort (CPUE) of Post-Larval Colorado squawfish, Interagency Standardized Monitoring Program, 1988. TOTAL TOTAL TOTAL MEAN NUMBER AREA COLORADO CPUE RIVER/ OF SEINED SQUAWFISH (FISH/ STANDARD CORRECTION REACH SAMPLES (m2) COLLECTED 100 m2) DEVIATION FACTORa COLORADO PRIMARY BACKWATERS 1 44 2071 82 4.822 10.771 1.36 2 12 672 1 0.139 0.461 NOT USED GREEN 3 47 2041 1353 69.692 74.179 1.00 4 42 2170 538 38.451 79.459 1.15 SECONDARY BACKWATERS COLORADO 1 42 1993 2 8 484 GREEN 3 35 1174 4 42 1820 90 5.703 8.649 1.36 0 0.000 0.000 NOT USED 1539 150.538 299.069 1.00 347 18.608 40.253 1.15 based on the number of Colorado squawfish identified in the preserved samples. C/E was multiplied by this value for samples when no fish were preserved.