7333

• UCREFRP Catalog Number: 7333
• Author: Valdez, R. A. and W. J. Masslich.
• Title: Winter Habitat Study of Endangered Fish - Green River, Wintertime Movement and Habitat of Adult Colorado Squawfish and Razorback Suckers.
• USFW Year: 1989.
• USFW - Doc Type: Report No. 136-2 for Bureau of Reclamation,
• Copyright Material: NO

In year 1, eight adult razorback suckers
occupied slow runs, slackwaters, and eddies
52,27 and 21 percent of the time, respectively.

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OVERWINTERING ADULT COLORADO SQUAWFISH AND RAZORBACK SUCKERS
SELECT SPECIFIC MICROHABITAT WITHIN LOW VELOCITY HABITATS

In year 1, ten adult Colorado squawfish
occupied slow runs, slackwaters, eddies, and
backwaters 43, 39, 12, and 6 percent of the
time, respectively. Nine fish in year 2 occupied
these same habitats 64, 29, 2, and 5 percent of
the time, respectively. The same nine fish
monitored under ice-cover occupied slow runs,
backwaters, and slackwaters 69, 17 and 14
percent of the time, respectively. Thus,
sedentary fish occupy primarily slow runs and
slackwaters, as well as eddies and backwaters
to a lesser degree. The areas used by the fish
are characterized by average water depth of
2.5 to 4.5 feet, and mean column velocity of 0
to 1.0 fps.

Nine fish in year 2 occupied these same
habitats 71, 15 and 14 percent of the time,
respectively. The same nine fish monitored
under ice-cover occupied slow runs and eddies
81 and 19 percent of the time, respectively.
Sedentary fish occupy primarily slow runs and
slackwaters, as well as eddies to a lesser
degree. The areas used by the fish are
characterized by average water depth of 2.0 to
4.5 feet, and mean column velocity of 0.1 to 1.1
fps.

OVERWINTERING ADULT COLORADO SQUAWFISH APPEAR TO REST IN MIDCHANNEL
SLOW RUNS AND SLACKWATERS AND FEED IN EDDIES AND BACKWATERS

Average gross movement of adult Colorado
squawfish in eddies and backwaters (48.20
m/h) was significantly greater than in slow runs
and slackwaters (21.71 m/h) , indicating a
foraging behavior in the fonner habitats and a

resting mode in the latter. These observations
suggest that overwintering adult Colorado
squawfish rest in deep midchannel habitats with
low velocity, and they feed in shoreline eddies
and backwaters.

SIGNIFICANTLY GREATER LOCAL MOVEMENT IS EXHIBITED BY
ADULT COLORADO SQUAWFISH AND RAZORBACK SUCKERS EXPOSED TO
FLUCTUATING RIVER LEVELS THAT EXCEED 5 CM/H

Average gross movement of seven adult
Colorado squawfish ,exposed to flow
fluctuations of more than 5 cm/h was 66.89
m/h; this was significantly greater local
movement than under nonfluctuating conditions
(23.03 m/h). Average gross movement of three
razorback suckers exposed to flow fluctuations
of more than 5 cmth was 42.84 m/h; this was
significantly greater local movement than under

nonfluctuating conditions (30.93 m/h).
Microhabitats used by these fish are altered or
shifted by the fluctuating flows, causing the fish
to move. We conclude from these observations
that flow fluctuations greater than 5 cm/h
causes about 190 percent greater movement
by adult Colorado squawfish and 39 percent
greater movemenf by adult razorback suckers.

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