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 9
Gunnison (i.e., downstream from the Redlands
diversion dam; a few are isolated upstream), and
mainstem Colorado rivers (downstream from the
Grand Valley diversion dams; Fig. 1).
Colorado squawfish are long-lived piscivores
that grow to more than a meter in length and
exhibit long migrations (e.g., between White and
Yampa rivers; Tyus 1990) associated with 15-20°
C isotherms (my interpretation based on data in
Tyus 1984, 1990). The fish spawn on chute chan-
nels (Harvey et al. in press) that form on specific
alluvial bars in the Yampa and Green rivers (Fig.
2) in association with the decline of spring runoff
and spates (Nesler et al. 1988; Tyus 1990). Eggs
of squawfish hatch within about 5 days after
spawning at 20-22° C, which is the critical tem-
perature for successful reproduction (Hamman
1981; Haynes et al. 1984; Tyus and McAda 1984;
Marsh 1985). Upon hatching, larvae drift down-
stream (Fig. 3), where they are entrained in back-
water nursery habitats in alluvial reaches (shown
generally in Fig. 1). In lab experiments, young of
500
400
300
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100
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E

220
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140 100 60 '•4
1985
20 Z Meybeu
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JUN JUL AUG
the year (YOY) prefer and grow best at 25° C
(Black and Bulkley 1985). The YOY and juveniles
are most often found in specific low velocity envi-
ronments, created by the complex relationship of
flow and channel geomorphology (Fig. 2). These
nursery and rearing sites also are inhabited by
native and nonnative fishes, particularly flannel-
mouth sucker (Catostomus latipinnis), roundtail
chub, green sunfish (Lepomis cyanellus), red
shiner (Cyprinella lutrensis), sand shiner (Notro-
pis stramineus), and channel catfish (Ictalurus
punctatus), that compete with the endangered
fishes for available food resources or prey on them
directly (Valdez and Wick 1983; Karp and Tyus
1990). Adult squawfish also prefer areas of the
channel that are braided and complex, where low
velocity habitats (e.g., eddies, pools, and slow
runs) are abundant. Like razorback sucker, adult
squawfish tend to move in and out of large back-
waters that form on downstream ends of backbar
channels and terrace- or wall-based channels
(Fig. 2), which remain connected to the main
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., 3
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JUN JUL
so z
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400,
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1986
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5 10
AUG
Fig. 3. Relationships of Colorado River squawfish spawning dates (vertical bars, data derived from larval drift rates
adjusted for hatching time) to Yampa River flows measured at the Deerlodge and Maybell gauges in 4 years.
Number of fish represents number of larval fish sampled and distributed according to estimated spawning date
(from Nesler et al. 1988).
20 25 30 5 10 15 20 25 30 5 10
JUN JUL AUG
20 25 30 5 10 15 20 25 30 5 10
JUN JUL AUG