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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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.
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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
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 post-larval 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. However, it is impossible to determine whether Gmean CPE or estimated total
number of fish is more accurate when the two variables are not closely correlated with each
other. The correlations and the potential for unmeasurable error indicate that estimating
backwater error does not add to mean CPE as an index to relative abundance of Colorado
squawfish. Because of high cost and the long period required for data analysis, aerial video
should not become an annual component of ISMP.
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. It is an important
component of a nursery habitat study being conducted by UDVWR--its importance to ISMP
can be reassessed at the conclusion of that study. Measurement of physical habitat with
aerial video could also contribute to studies monitoring long-term channel changes in the
upper basin. Evaluating large-scale channel changes may be a more suitable use for aerial
video than trying to make precise measurements of backwater area and number.
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