7733

• UCREFRP Catalog Number: 7733
• Author: McAda, C. W.
• Title: Evaluation of Aerial-Video Measurement of Backwaters as Part of the Interagency Standardized Monitoring Program for Age-0 Colorado Squawfish.
• USFW Year: 1993.
• USFW - Doc Type: \
• Copyright Material: NO

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EXECUTIVE SUMMARY
Aerial video has provided important information about physical habitat in the large ,
rivers of the Upper Colorado River Basin and can continue to do so. However,
measurement of backwater surface area with aerial video does not add substantially to mean '
catch per effort (CPE) as an index to relative abundance of YOY Colorado squawfish in fall
and therefore should not become a permanent component of the Interagency Standardized '
Monitoring Program (ISMP).
ISMP estimates the relative abundance of young-of-the-year YOY Colorado squawfish in ,
important nursery areas in the Green and Colorado rivers every fall. Relative abundance is
determined by the mean CPE of small Colorado squawfish captured from backwaters in these '
important river reaches. These data are used to monitor trends in abundance among reaches
and rivers, and to evaluate the effect of various biological and physical parameters on
reproductive success, growth, and survival of YOY Colorado squawfish. '
As the program progressed, participants became concerned that mean CPE alone was '
not providing an accurate index of relative abundance every fall. They felt that estimates of
relative abundance could be improved by measuring the number and surface area of
backwaters within ISMP reaches. Therefore, aerial video was incorporated into ISMP on a '
trial basis to examine its potential for measuring number and surface area of backwaters and
improving the annual estimate of relative abundance. It was felt that a gross estimate of total '
number of small Colorado squawfish could be obtained by multiplying mean CPE by total
area of backwaters. '
This report evaluated three years of ISMP data collected in conjunction with aerial video
enumeration of backwater number and area. Aerial video was collected over relatively short
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periods of time, while ISMP sampling (which the video was designed to supplement) often
required considerably longer. Streamflow, and therefore backwater area, could change '
markedly during the interval between backwater measurement and fish collections,
introducing substantial error into the calculations. Large flow changes occurred during the
data collection period in every reach at least once during the three years reported here. '
These flow changes introduce considerable error into calculations that appear to be quite
precise. Using these numbers to estimate total number of YOY Colorado squawfish implies ,
more precision than actually exists.
Mean CPE and the estimated number of Colorado squawfish were positively correlated '
with each other in many instances examined in this report. It is impossible to determine
whether mean CPE or estimated total number of fish is more accurate when the two variables ,
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