7048

• UCREFRP Catalog Number: 7048
• Author: Desert Fishes Council ‎(Edwin Pister, e.
• Title: Proceedings of the Desert Fishes Council
• USFW Year: 1991.
• USFW - Doc Type: Volumes XX and XXI
• Copyright Material: NO

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We believe the use of these four habitat types reflects as least two
behaviors; resting and feeding. Overwintering adult Colorado squawfish appear
to rest in slow midchannel runs and slackwaters, and feed in eddies and
backwaters. This hypothesis is based on the relatively sedentary nature of the
radiotagged fish while in slow runs and slackwaters and a greater amount of
local movement while in eddies and backwaters. Colorado squawfish in year 2
exhibited different degrees of movement in the two habitat categories
identified above. Movement of 9 fish in slow runs and slackwaters (n = 12;
mean = 21.71 m/h; SD = 22.92) differed significantly (Student's t = 1.70; P >
0.90) from their movement in eddies and backwaters (n = 10; mean 48.20 m/h;
SD - 49.27). The greater degree of movement in eddies and backwaters is
attributed to foraging for prey species which are probably more abundant in
these habitats than in midchannel runs and slackwaters.
Selection of wintertime microhabitat by adult Colorado squawfish appears
driven by low average (at 0.6 depth) and near-bottom velocity and an average
minimum depth requirement of about 3.5 feet (Table 1). Fish were observed in
three separate habitat categories in similar watercolumn depths and velocities
under ice and ice-free conditions. These areas were not necessarily the
deepest parts of the river channel, and we believe the fish were positioned
near the bottom where velocities were low, although river turbidity did not
allow us to observe them directly. We also recognized that the fish were
commonly associated with an instream cover element. Adult Colorado squawfish
were frequently seen resting in slow runs and slackwaters immediately
downstream of a sand shoal that appeared to slow water velocity at the fish
location. Often the fish were located in a small depression or trough created
by sand waves.,,as.is reflected by the dominant run/slackwater substrate.
Although the fish frequented shallow water under ice, the depth
measurements do not reflect this because the fish were too mobile to meet the
minimum 15-minute criterion for habitat measurements. Thus, depth and velocity
measurements collected in this investigation probably reflect primarily resting
habitat. Measurements were not taken on fish that were continually active.
The relatively greater number of observations (measurements) in runs and
slackwaters (Table 1) supports the hypothesis that adult Colorado squawfish
rest principally in these habitat types.
Razorback Sucker
During the first winter of this investigation, 8 radiotagged razorback
suckers were observed in three habitat types; runs, slackwaters, and eddies.
The fish occupied these ice-free habitats 46, 24, and 30% of the total
observation time, respectively (Figure 7).
The 9 radiotagged fish monitored the second winter, under ice-free
conditions, used runs, slackwaters, and eddies 71, 15, and 14% of the time,
respectively (Figure 7). The same 9 fish monitored under ice-covered
conditions during year 2 occupied runs and eddies 81 and 19% of the time,
respectively.
Unlike adult Colorado squawfish, adult razorback suckers not exposed to
fluctuating flows in year 2 did not exhibit different degrees of movement in
the two habitat categories identified above. Movement of 8 fish in slow runs
and slackwaters (n - 19; mean = 31.94 m/h; SD = 35.92) was no different
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