9583

• UCREFRP Catalog Number: 9583
• Author: BIO/WEST Inc.
• Title: Annual Summary Report 1993 - Survival of Age-0 Colorado Squawfish in the Green and Colorado Rivers ‎(UDWR Contract No. 90-2558)‎.
• USFW Year: 1994.
• USFW - Doc Type: Logan, UT.
• Copyright Material: NO

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Table 1. Trip schedules for age-0 Colorado squawfish sampling of the Colorado and Green Rivers,
1987-1993.
Trip Reach 1 Reach 3 Reach 4
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 September 27 - 298
Spring 1990 March 22 - 25 March 20 - 24 Apri12 - 4
Fall 1990 September 19 - 20 September 17 - 20 September 24 -268
Spring 1991 March 23 - 24 March 20 - 23 April 1 - 3
Fall 1991 September 16 - 19 September 16 - 19 September 23 - 268
Spring 1992 March 22 March 18 - 21 April 1 - 3
Fall 1992 September 21 - 248 September 21 - 248 October 5 - 78
Spring 1993 April 1 - 2 March 29 -April 1 April 5 - 7
Fall 1993 September 21 - 248 September 21 - 248 September 27 - 298
eSampled by UDWR
The methodology employed is similar to that described in the ISMP Handbook (U.S. Fish and Wildlife Service
1987). Two backwaters were sampled every 5 miles within each sample reach using 1/8-inch ace mesh beach
seines, 15 ft long by 4 ft deep. Two seine hauls were taken at each backwater, the fish in each counted, and
all endangered fish measured (total length) 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-0 squawfish. This method is being used
by the Service's Database Manager on ISMP data (Personal communication, C. McAda, February 24, 1992).
It involves a log transformation of CPE's, primarily because catch data for Colorado squawfish in backwaters
are highly variable.
The geometric mean calculation method was as follows: First, a CPE for age-0 squawfish was computed for
each seine haul (age-0/100mz). 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:
' GM~E = antilog ((1/n) E In (CPE + 1)J - 1
where: GM~E = geometric mean catch per effort
' CPE catch per effort of age-0 squawfish (age-0/100mZ)
n total number of seine hauls (with and without target fish)
The advantage to this approach is that it reduces variation by making the variance independent of the mean.
However, log transformations tend to weight higher CPE's less.
~ '