7758

• UCREFRP Catalog Number: 7758
• Author: Stanford, J. A. and P. C. Nelson.
• Title: Instream Flows to Assist the Recovery of Endangered Fishes of the Upper Colorado River Basin.
• USFW Year: 1994.
• USFW - Doc Type: Denver, Colorado.
• Copyright Material: NO

INSTREAM FLOWS TO ASSIST THE RECOVERY OF ENDANGERED FISHES 11
Squawfish distribution in Colorado River
(1991-1992)
50
t 40 -
35
3
E 30-
Z
Z
20
10---
8 1
10
4 2
15-mile sections of river
Squawfish average length in Colorado River
(1991-1992)
600
E
E
500
m
J
400
300
200
15-mile sections of river
Dynamic Relationships Between Flow,
Channel Geomorphology, and Food Webs
Distribution, abundance, and life histories of the
endangered fishes seem to be strongly influenced
by availability of physical habitats that are created
and maintained by flow dynamics in time and space
(Fig. 6). Indeed, squawfish only spawn on clean
cobble on specific bars in the sediment-laden river
segments of the Upper Colorado system. Hence, a
fundamental process-response relationship in-
volves the movement of the fish to the bars in
concert with flows that first form the bars and then
flush sediment off of cobble substratum so that the
fish can spawn successfully (Fig. 2; Tyus 1990;
Harvey et al. in press). Humpback chub primarily
occur in eddies and other hydraulically complex
habitats found in constrained channels in the
steeper gradient segments within canyons (Fig. 2;
700
Fig. 5. Distribution of squawfish by size
and number caught in the Colorado
River from the Green River confluence
(km 0) to the Grand Valley diversion
dam at the top of the 15-mile reach
during 1991-1992. This relationship,
although variable, is remarkably con-
sistent from year to year; the upstream
areas inhabited by by larger adults are
consistently devoid of young-of-the-
year squawfish relative to the river
segment below Westwater Canyon and
the confluence with the Green River
(km 179-0) (Doug Osmundson, U.S.
Fish and Wildlife Service, Grand Junc-
tion, Colorado, unpublished data).
Kaeding and Zimmerman 1983; Kaeding et al.
1990; Karp and Tyus 1990; Valdez et al. 1990).
Squawfish and razorback sucker are almost always
captured in low or zero velocity habitats (Tyus 1984;
Osmundson and Kaeding 1989), which occur within
the active channel (e.g., eddies) or exist as backwa-
ters (e.g., back-bar channels) or floodplain wetlands
(i.e., flooded bottomlands) that are continually or
seasonally attached to the active channel. Squaw-
fish (Tyus 1991a, 1991b), and perhaps razorback
sucker (Minckley et al. 1991), must have access to
low velocity environments to mature. These obser-
vations strongly imply that low velocity habitats
are important feeding or resting areas or both, but
they do not imply that rivers of consistently low
velocity or volume are most suited to the endan-
gered fishes of the Upper Colorado River Basin.
Low velocity environments are formed and
maintained by complex hydrologic processes that