9685

• UCREFRP Catalog Number: 9685
• Author: Tyus, H. M. and C. A. Karp.
• Title: Habitat Use and Streamflow Needs of Rare and Endangered Fishes
• USFW Year: 1989.
• USFW - Doc Type: Flaming Gorge Studies - 2nd Preliminary Draft.
• Copyright Material: NO

Report 10- Age Determination in Colorado Squawfish and Razorback Sucker
(Hinckley et al ., in prep.).
A total of 47 Colorado squawfish (317-800mm TL) and 13 razorback sucker
(500-560mm TL) collected from the Green, White, and Yampa rivers, 1974-1986
were aged by sectioned and polished otoliths and by vertebral centra.
Additional museum specimens of six Colorado squawfish (collected 1962-1970)
and eight razorback sucker (collected 1926-1982) from various locations were
also aged. Colorado squawfish ranged in age from 3 to >3i years and razorback
sucker were 20 to >40 years of age. Ages of similar-size Colorado squawfish
were generally the same between old (pre-1970) and recent collections.
Razorback suckers collected in the Green River were all-old fish (average 27
years), presumably hatched before closure of F]aming Gorge Dam, whereas one
fish collected in 1961 was only 5 years of age. Although based on a limited
number of specimens, this study suggested that Colorado squawfish are
recruiting to the existing population and age-size relationships are similar
to the past. Razorback sucker recruitment has been limited or nonexistent in
the Green River since the 1960s (Preliminary Abstract).
Study 4: Fish Community interactions
Report 11- Influence of Environmental Factors on Distribution and Abundance of
Age-0 Colorado Squawfish in the Green River, Utah (Haines and Tyus, in
review).
Habitat use and species associations of age-0 Colorado squawfish.
Ptychocheilus Lucius were evaluated in the Green River, Utah, 1979-88. The
fish was more abundant (38%) than other species in the summer drift, which
included suckers Catostomus spp. (33%), speckled dace Rhinichthys osculus
(i4%), and channel catfish Ictalurus punctatus (3%; n = 1,706). However, age-
0 Colorado squawfish comprised only 3% of summer backwater seine catch, which
was dominated by non-native red shiner Notropis lutrensis (87%; n = 102,033).
in autumn, age-0 Colorado squawfish were captured in 57% of the backwaters
seined, but comprised only 6% of a catch (n = 67,179) dominated by non-native
red shiner (65%) and fathead minnow Pimephales promelas {16%). Colorado
squawfish and most other fishes inhabited a wide range of environmental
conditions, but were most abundant in backwaters of water depth greater than
15 cm. Red shiner and fathead minnow were abundant in habitats used by young
Colorado squawfish, suggesting potential resource sharing. In general, fish
abundance was highest in years of warmer temperatures and lower flows. High
spring and summer flows were associated with lower standing crops in autumn.
We detected no segregation in habitat use between young Colorado squawfish and
non-native fish, however proliferation of these introduced fishes should be
further evaluated as a factor associated with the decline of Colorado
squawfish (Preliminary Abstract).
Report 12- Diets of Young Colorado Squawfish and Other Fishes in Backwater
Habitats, Green River (Muth et al ., in prep).
Diets of young Colorado squawfish and other fishes in backwater habitats
were investigated summer and fall 1986-1987. Analyses of about 1,IOO Colorado
squawfish stomachs {fish ranging in length from 7.5-113mm total length)
indicated a predominance of chironomid larvae and cyclopoid zooplanktan. Of
all stomachs containing food {95%), less than 1% (n=9, 20.6-73mm total length)
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