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

Table 6. Total number of backwaters (> 30m) and total area of backwaters (> 30m') within ISMP
reaches as determined by aerial video, and mean-daily streamflow (mean during video-
collection period) at the nearest USGS stream gauge, 1989 to 1991.
Backwaters Backwaters
Discharge Total Total Discharge Total Total
Year (CFS) Number Area (CFS) Number Area
- Reach 1 -- -- --------------------------
1989 Reach 2
3,015 169 135,422 2,990 78 64,120
1990 3,855
1991 5,045
1989 1,640
1990 1,370
1991 2,650
207 90,858 3,490 84 140,880
137 87,255 5,070 68 73,519

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--- Reach 3 Reach 4
115 68,201 1,400 406 280,463
256 158,988 1,265 375 322,952
95 45,702 1,915 267 208,051
(Appendix Table A6). There were several other instances when fewer than eight seine hauls
were taken in a 10-mile reach (the maximum number of seine hauls under ISMP protocol),
but sufficient numbers of backwaters to accommodate all eight seine hauls were identified
from the video (again, presumably because field crews judged some of the backwaters as
unacceptable due to shallow depth or slight water flow; factors unmeasurable from video
interpretation). These apparent contradictions illustrate the difficulty of incorporating
parameters other than surface area into video interpretation.
Catch Rate of YOY Colorado Squawfish in Relation to Backwater Area
The primary reason for determining backwater area was to estimate the total number of
YOY Colorado squawfish in fall using mean catch per effort (CPE) and total area of
backwaters. Gmean CPE was intended to monitor trends in abundance of YOY Colorado
squawfish from one year to the next and among the four reaches sampled by ISMP. Since
total area of backwaters (> 30 m) is known, total number of fish in backwaters could be
estimated by multiplying Gmean CPE (fish per m) by total area of backwaters (m2). We are
still not getting a true total because fish in habitats other than backwaters are not considered
and there is some unknown degree of error associated with preferential use of certain types
of backwaters. To determine if major differences existed between trend data (Gmean CPE)
and the estimate of total number of fish available in the fall, the two parameters were plotted
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