8064

• UCREFRP Catalog Number: 8064
• Author: McAda, C. W., et al.
• Title: Interagency Standardized Monitoring Program
• USFW Year: 1997.
• USFW - Doc Type: Summary of Results, 1996 - Annual Report.
• Copyright Material: NO

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 secondary 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 standard calculation of arithmetic 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
((2.71828"°)-1). A log transformation improves the normality of CPE data, but
unfortunately, low catch rates still result in non-normal data in many 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 11 years of ISMP.
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