7046 ‎(3)‎

• UCREFRP Catalog Number: 7046
• Author: Valdez, R. A., W. J. Masslich and A. Wasowicz.
• Title: Final Report\
• USFW Year: 1992.
• Copyright Material: NO

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EXECUTIVE SUMMARY

BIO/WEST, Inc. conducted an investigation in 1990 and 1991 to determine the suitability of the
Dolores River for endangered Colorado River fIshes. Physical, chemical, and biological attributes
were assessed in six reaches of the lower 177 miles from BradfIeld Bridge to the confluence with the
Colorado River, The investigation was funded by Utah Division of Wildlife Resources (UDWR) and
Bureau of Reclamation (Reclamation) through the Recovery Implementation Program for
Endangered Fish Species in the Upper Colorado River Basin, The study was conducted in
cooperation with UDWR, Colorado Division of Wildlife, and U.S. FISh and Wildlife Service.

Nineteen species of fish were captured, including six native species and thirteen non-natives.
Native species included Colorado squawfish (Ptychocheilus lucius), roundtail chub (Gila robusta),
flannelmouth sucker (Catostomus latipinnis), bluehead sucker (C, discobolus), speckled dace
(Rhinichthys osculus), and mottled sculpin (Cottus bairdi). The most common non-native species
were red shiner (Cvorinella lutrensis), sand shiner (Notropis stramineus), fathead minnow
(Pimephales promelas), carp (Cyprinus carpio), and channel catfISh (Ictalurus punctatus). Native
species composed 19 percent of total fish numbers, which was four times higher than the adjacent
Colorado River, and indicative of a relatively good native fish fauna. No significant changes in
species composition were evident when compared to a similar survey in 1981, indicating that the
ichthyofaunal community remained relatively stable over the last ten years.

Four Colorado squawfish were captured within 2 km of the confluence with the Colorado River
in August and October, 1991. The species was reported in the Dolores River in the 1950's and
1960's, but spills of uranium mill wastes in the lower San Miguel River in mid-l960 killed most of the
fish in the lower 60 miles of the Dolores River, Colorado squawfish were not captured in surveys
in 1971 and 1981, and seven squawfish reported from the lower 6 miles of the San Miguel River in
1973 were unconfirmed.

Cross-sectional analyses, habitat mapping, and comparisons with the Yampa and White rivers
revealed that the Dolores River channel was suitable for all life stages of Colorado squawfish, but
low flows during this investigation reduced fISh habitat value, Deep pools and adjacent gravel/cobble
riffles were judged suitable for holding adults and juveniles, and for staging and spawning. Backwater
formation was limited and ephemeral, reducing the value of the Dolores River as a nursery for young
Colorado squawfish, However, the Dolores River confluence was tocated immediately upstream of
a major nursery on the Colorado River.

Water quality appeared suitable for Colorado squawfish most of the year. Removal of uranium
mill wastes reduced levels of radionucleides and heavy metals, However, during summer flood events
associated with high intensity rain storms, copper and iron were released into the system at potentially
lethal levels from either instream sediments or tributary input of erodible soils. High water hardness
may ameliorate toxic effects of these elements but further study is required to assess potential impacts
of heavy metals.

McPhee Dam, constructed in 1984 about 200 miles upstream of the confluence with the Colorado
River, has reduced high spring flows and augmented base summer, fall, and winter flows. Base flow
releases of 20 to 40 cfs in 1990 and 1991 reduced native fish habitat in the lower 170 miles of the
Dolores River through decreased fish holding areas, dewatered nursery backwaters, impeded
movement, and enhanced sedimentation. We recommend minimum base flow releases of 50 cfs
during dry and normal years, and 78 cfs during wet years,

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