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I I I I I I I I I I I I I I I I I I I Table 1. Trip schedules for age-O Colorado squawfish sampling of the Colorado and Green Rivers, 1987-1992. Trip Reach 1 Reach 3 Fall 1987 September 23 - 24 September 23 - 24 Spring 1988 March 24 - 25 March 21 - 22 Fall 1988 September 29 - 30 September 26 - 28 Spring 1989 March 22 - 23 March 20 - 22 Fall 1989 September 24 - 26 September 20 - 23 Spring 1990 March 22 - 25 March 20 - 24 Fall 1990 September 19 - 20 September 17 - 20 Spring 1991 March 23 - 24 March 20 - 23 Fall 1991 September 16 - 19 September 16 - 19 Spring 1992 March 22 March 18 - 21 Fall 1992 September 21 - 243 September 21 - 243 3Sampled by UDWR Reach 4 September 27 - 29" April 2 - 4 September 24 - 263 April 1 - 3 September 23 - 263 April 1 - 3 October 5 - 73 The methodology employed is similar to that described in the ISMP (U.S. Fish and Wildlife Service 1987). 1\vo backwaters were sampled every 5 miles within each sample reach using 1I8-inch ace mesh beach seines, 15 ft long by 4 ft deep. 1\vo seine hauls were taken at each backwater, the fish in each counted, and all endangered fish measured and released. Depths and dimensions of each backwater and seine haul were taken. Water depth, temperature and substrate type were recorded for all seine hauls. Catch per effort (CPE) was computed using all seine hauls. The geometric mean of the CPE was used to compare densities of age-O squawfish. This method is being used by the Service's Database Manager on ISMP data (Personal communication, Chuck McAda, February 24, 1992). It involves a log transformation of CPE's, primarily because catch data for Colorado squawfish in backwaters are not normally distributed. The geometric mean calculation method was as follows: First, a CPE for age-O squawfish was computed for each seine haul (age-O/100m2). Then a '1' was added to the CPE of each seine haul to account for zero catches. This adjusted CPE was transformed to a natural logarithm. The transformed values were averaged, by reach and year, and the antilog of the average minus '1' yielded the geometric mean. Standard deviation was computed from log-transformed values, and the antilog taken to provide bounds around the geometric mean. The computation is expressed as follows (Sokal and Rohlf 1987): GMCPE = antilog [(lIn) 1:: In (CPE + 1)] - 1 GMCPE = geometric mean catch per effort CPE = catch per effort of age--O squawfish (age-O/100m2) n = total number of seine hauls (with and without target fish) where: The advantage to this approach is that it considers non-normally distributed data, and reduces variation by making the variance independent of the mean. However, log transformations tend to weight higher CPE's less. 3