8208

• UCREFRP Catalog Number: 8208
• Author: Osmundson, D. B., P. Nelson, K. Fenton and D. W. Ryden.
• Title: Relationships Between Flow and Rare fish Habitat in the '15-Mile Reach' of the Upper Colorado River.
• USFW Year: 1995.
• USFW - Doc Type: \
• Copyright Material: NO

FISH HABITAT USE
General
Selection of mesohabitats by adult Colorado squawfish and razorback sucker changes seasonally.
Osmundson and Kaeding (1989) documented year-round frequency of use of eight habitat types in
the Grand Valley during 1986-1988 by identifying the position of individual fish once weekly using
radiotelemetry (Appendix tables III and IV). The authors later reported (Osmundson and Kaeding
1991) three major seasons in which habitat selection by Colorado squawfish was distinctly
different: winter (November-February), spring (April-June) and summer (July-September).
October and March were reported as transitional periods during which the fish shift in and out of
their winter behavioral mode (Fig. 3). Depth of sites selected by squawfish also varied with time of
year (Fig. 4). Habitat seasonality of razorback sucker was similar to Colorado squawfish though
some differences were noted. To manage the river to provide favorable habitat, flows must also
change in a seasonal manner that corresponds to the fishes' season-specific, habitat needs. Here we
reexamine the seasonality of habitat use and suggest a somewhat different partitioning of the year
for purposes of flow management. The following provides a review of habitat seasonality as
determined during 1986-1988 and includes data from both the 15- and 18-mile reaches (see
Osmundson and Kaeding 1989 for methodology). Monthly frequency of use for each habitat type
was calculated by dividing the sum of all locations per month by the number of locations in that
type.
Adult Colorado squawfish
Winter
Between November and February, adult squawfish remain in localized segments of river, primarily
low velocity habitats. Seventy-four percent of squawfish locations had mid-column velocities <1.0
ft/sec. Pools and runs accounted for 77-95% of all mesohabitats used during any given winter
month; pools comprised 42-62%; runs, 27-41 %. All run habitat used was <2.0 ft/sec (slow runs).
Eddies and backwaters were the only other habitats that squawfish were located in during winter.
Eddies accounted for 5-8% of fish locations during January and February only, while large, chute-
channel backwaters were used by some fish all winter accounting for 5-15% of fish locations.
Spring
During spring, when water velocities are high and main-channel temperatures still relatively low,
squawfish often seek out warm, off-channel, low- to zero-velocity sites. Backwaters and flooded
gravel pits together comprised 45% of squawfish location sites during April; 49% during May; 47%
during June. Some use was also made of eddies (2-9%) and shorelines (3-8%). Use of riffles and
rapids was negligible (1-2% during Mayor June only). Selection of runs changed toward the end
of spring when use of higher velocity sites increased: slow runs declined in use from 32% in April
to 27%m' May to 13% in June; during the same period, fast runs increased in use from 0-3% to
19%.
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