7047

• UCREFRP Catalog Number: 7047
• Author: Tyus, H. M. and C. A. Karp.
• Title: Habitat Use and Streamflow Needs of Rare and Endangered Fishes in the Green River, Utah
• USFW Year: 1991.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

and upland vegetation is invading the flood zone. As this vegetation becomes
established, it accumulates sediment and reduces the availability and quality
of flood zone habitats (Fisher et al. 1983). The accumulation of sediments by
plants such as saltcedar (Tamarix pentandra) under controlled flows is of
particular concern relative to changing river channel morphology (Graf 1978).
Backwaters used by young Colorado squawfish are also used by other fishes,
and the squawfish were sympatric with adults and young of 22 other fish
species in backwaters of the Green River, where they comprised 6% of standing
crops (Haines and Tyus 1990). No evidence of resource partitioning between
young Colorado squawfish and these fishes was detected when fish densities
were contrasted against backwater depth, temperature, size, or substrates;
however, the abundance of most species was weakly correlated with the presence
of Colorado squawfish (Haines and Tyus 1990).
Effects of competition and predation by introduced fishes on growth and
survival of young Colorado squawfish have yet to be adequately assessed, but
the common use of backwater habitats and foods by young Colorado squawfish and
other small introduced fish species (e.g., channel catfish, green sunfish
Lepomis cyanellus, red shiner Notropis lutrensis; Jacobi and Jacobi 1982;
McAda and Tyus 1984; Muth et al., in prep) is evidence of negative
interactions. Karp and Tyus (1990b) suggested that growth and survival of
young Colorado squawfish may be adversely affected by the aggressive behavior
of introduced green sunfish, red shiner, and fathead minnow, PimeQhales
promelas. This may be most acute when increases or decreases in river level
reduces the availability of quality backwater habitat and causes resource
limitation. We assume that some non-native fishes prey on larval Colorado
squawfish (and other native forms), but the extent and significance of such
predation is as yet unknown.
There is some indication that abundance of non-native fishes may be
adversely affected by periods of high flow, whereas native species appear to
be little impacted (Haynes and Muth 1984; Minckley and Meffe 1987; T. Nesler,
written communication). However, the hypothesis that native Colorado River
fishes exhibit greater tolerance to extreme flooding has not been adequately
tested. In the Green River, abundance of Colorado squawfish and red shiner in
backwaters was lowest in years of high summer flows (Haines and Tyus 1990).
Backwater nursery habitats were influenced by inundation and
resuspension of organic material from shorelines during increased flows, and
this energy source was important for standing crops of fish food organisms
(Grabowski and Hiebert 1989). Backwaters in the Ouray area, where young
Colorado squawfish were most abundant, were richer in food than upstream areas
studied. Reduced water-level fluctuations in that area resulted in more stable
backwater habitats, and possibly reduced the export of nutrients and food
(Grabowski and Hiebert 1989).
Juveniles
Little is known about the habitat requirements of juvenile Colorado
squawfish, but they have been captured in a variety of shoreline habitats
including backwaters and flooded bottomlands. Although usually considered
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