7816

• UCREFRP Catalog Number: 7816
• Author: Tyus, H. M.
• Title: Movement and Habitat Use of Young Colorado Squawfish in the Green River, Utah
• USFW Year: 1991
• USFW - Doc Type: Journal of Freshwater Ecology
• Copyright Material: YES

Young Colorado squawfish were captured by selnlng shoreline
habitats with 5 m X 1 m seines of 3.2 X 4.8 mm woven mesh. All Colorado
squawfish were counted and measured (total length, TL). In 1979, fish
were placed in 10 mm size-classes. Beginning in 1980, TL was determined
by measuring each individual squawfish to the nearest mm. All young
Colorado squawfish captured in April and October were marked by cutting
a tiny piece from the margins of the caudal and dorsal fins with a pair
of scissors. This marking was done to identify recaptures and to
determine movements of marked fish from one habitat to another. Capture
of marked fish in which the upper lobe of the caudal fin was marked
indicated that the fish was previously captured in a backwater; fish
with the lower lobe marked indicated a shoreline; and a marked dorsal
fin indicated an eddy. Efforts in November, 1981, were to recapture
marked fish from previous sampling; thus, other fish were not marked at
that time.
Sudden and unexpected spates in November, 1981, increased the water
depth about 25 em. This inundated study backwaters and changed them to
eddies and runs. Only data collected during a period of steady flow
(2030 h on 4 November to 0100 h on 5 November) were used to evaluate
fish movements in backwaters with response to water temperatures.

RESULTS

A total of 1,194 young Colorado squawfish were captured in
backwaters, eddies and shoreline runs. Of these, 922 fish were marked by
fin-clipping, and 234 were subsequently recaptured. Most of the fish
(84.7%) were captured in shallow shoreline embayments (backwaters), and
they were most abundant in April (67.9%, Table 1). Colorado squawfish
were mobile, and movements between backwaters, eddies, and shoreline
habitats were detected. However, some marked fish remained in the same
general area for one month. Marked fish were also recaptured on the
other side of the river channel from where they were originally marked
(Table 1, Figure 2), demonstrating an ability to swim across river
currents.
Backwaters sampled in autumn of 1979 produced 49 age-O Colorado
squawfish ranging in size from 30 to 60 mm TL and all fish were captured
in the morning and afternoon samples. Ten fish (20.4%) that were marked
during the first day were subsequently recaptured (Table 1). Young
squawfish were captured at backwater temperatures of about 5.90C (range
4-60C). Water temperatures of the main channel (MC) and backwaters (BA)
were measured at three times on 1 November: 1200 h, MC- 50C, BA- 70C;
1400 h, MC- 60C, BA- 100C; and 2300 h, MC- 50C, BA- 40C.
Sampling in April 1980 produced 632 yearling (age-I) Colorado
squawfish, of which 511 were marked as new captures (x- 51 mm TL, SO= 8)
and 121 (23.7%) were recaptured (Table 1). Most captures were made in
the backwater (91.5%), but 5.5% were captured in the eddy, and 3% were
captured in shoreline runs. Of the 467 fish marked in the backwater,
110 were recaptured, including 102 in the backwater, five in shoreline
runs, and three in the eddy (Table 1). Of 31 fish marked in the eddy,
11 were recaptured, including nine in the backwater, one in a run, and
one in the eddy. These recaptured fish indicated that young Colorado
squawfish move among habitats. Highest catches corresponded with mid-
afternoon temperatures of 20 and 210C on day 1 and 4, and lower catches
on days 2 and 3 were associated with afternoon temperatures of only 13
and 140C. Lowest catches always occurred in mid-morning and were
associated with water temperatures of 9-130C. Backwater temperatures
were similar to main channel temperatures in early morning but were 3-
90C higher in afternoon.

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