7154

• UCREFRP Catalog Number: 7154
• Author: Holden, P. B.
• Title: Habitat Requirements of Juvenile Colorado River Squawfish.
• USFW Year: 1977.
• USFW - Doc Type: FWS/OBS-77/65,
• Copyright Material: NO

14

Although U, S. Geological Survey flow records for August and
September were not available for inclusion in this report, flow levels
of the Green River appeared lower than normal. It is quite probable
that the low water year experienced in 1977 caused a reduction in ~iver
flow. Personal observation indicated the Yampa River was exceptionally
low.

The preferred depth, velocity, substrate, habitat type, and
temperature of the rare fishes are summarized as electivity curves (Fig-
ures 3-10). Colorado squawfish young-of-the-year were found only in back-
waters where there was no current, a firm silt bottom, and a depth of
one to two feet (Figure 3), Juvenile squawfish also preferred backwaters,
no current and a silt bottom, but were less selective with depth (Figure
4). Subadult and adult squawfish (200+ mm) were found in a variety of
velocities and depths, but preferred sandy bottomed eddies and runs to
backwaters (Figure 5). Squawfish of all sizes showed little preference
for temperature as they were found in almost the entire range of tempera-
tures encountered during the study (Figure 6).
The six young-of-the-year razorbacks collected showed a preference
for eddies with a velocity of about 0.2 fps (feet per second), a depth
of 1.0 foot, and a soft silt bottom.
Humpback chub young-of-the-year (Desolation and Gray canyons fishes)
were less selective of microhabitat than were yound squawfish. The young-
of-the-year chubs preferred backwaters with no current, a firm silt bottom,
and two feet of maximum depth, but also used deeper eddies and runs with
velocities from 0.4-0.8 fps (Figure 7). Juvenile humpback chubs used a