8188

• UCREFRP Catalog Number: 8188
• Author: Muth, R. T., et al.
• Title: Flow and Temperature Recommendations for Endangered Fishes in the Green River Downstream of Flaming Forge Dam.
• USFW Year: 2000.
• USFW - Doc Type: \
• Copyright Material: NO

Final Report

4-6

September 2000

tailwater releases, which are managed not to exceed 130C, are well below the 170C optimum
temperature for growth of nonnative rainbow trout (Hokanson et al. 1977), the main species of
interest in the tailwaterfishery. Native fishes also benefitted from thermal enhancement ofthe Green
River. Within 6 months after .the penstock modifications, Holden and Crist (1981) documented
re-invasion and reproduction by common warm-water native fishes and nonnati ve fishes in the Green
River upstream of the Yampa River confluence. The presence of adult Colorado pikeminnow and
razorback suckers was documented, but reproduction by either species was not observed, and
humpback chubs and bonytails were not found. Filbert and Hawkins (1995) suggested that increasing
the temperature of releases from Flaming Gorge Dam to levels greater than l30C may improve
thermal conditions for tailwater trout and for native fishes downstream.

4.1.2 Nonnative Fishes

A total of 25 nonnative fish species in nine families has been reported from reaches of the
main-stem Green River between Flaming Gorge Dam and the Colorado River confluence and from
lower portions of tributaries (see Table 4.2 at the end of this section). Of the cool- or warm-water
nonnative fishes, red shiner, common carp, sand shiner, fathead minnow, and channel catfish are
widespread and common to abundant; redside shiner, white sucker, black bullhead, northern pike,
green sunfish, and smallmouth bass are locally rare to common in some river reaches or habitats; and
grass carp, Utah chub, creek chub, Utah sucker, western mosquitofish, brook stickleback, bluegill,
largemouth bass, black crappie, and walleye are incidental to rare. Salmonids are generally restricted
to Reach 1 and are most abundant in the tail waters of Flaming Gorge Dam.

Nonnative fishes dominate the ichthyofauna of Colorado River basin rivers and have been
implicated as contributing to reductions in the distribution and abundance of native fishes as a result
of competition and predation (Carlson and Muth 1989). Behnke and Benson (1983) attributed the
dominance of nonnative fishes to dramatic changes in flow regimes, water quality, and habitat
characteristics. They reported that water development has converted a turbulent, highly variable river
system into a relatively stable system, with flow and temperature patterns that allowed for the
proliferation of nonnative fish species. Hawkins and Nesler (1991) identified red shiner, common
carp, fathead minnow, channel catfish, northern pike, and green sunfish as the nonnatives considered
by Colorado River basin researchers to be of greatest concern because of their suspected or
documented negative interactions with native fishes. Sand shiner, white sucker, black bullhead,
smallmouth bass, and largemouth bass were identified by Hawkins and Nesler (1991) as nonnatives
of increasing concern because of their increasing abundance, habitat preferences, and/or piscivorous
habits. Life histories of nonnative fishes in the upper Colorado River basin and their potential effects
on native fishes were reviewed by Lentsch et al. (1996b).

Lentsch et al. (1996b) and Tyus and Saunders (1996) presented options for controlling
nonnative fishes in the upper Colorado River basin. Those options included more restrictive stocking
protocols, reduction or elimination of escape from existing stocks, more liberalized harvest