9378

• UCREFRP Catalog Number: 9378
• Author: Nesler, T. P.
• Title: Recovery of the Colorado River Endangered Fishes
• USFW Year: 2000.
• USFW - Doc Type: Biological recovery goals and criteria for Colorado pikeminnow, Humpback chub, Razorback sucker & Bonytail.
• Copyright Material: NO

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protected over the long term to insure populations of the listed fish species
continue to be sustained at or better than the biological recovery goals.

Population-level data describing the status and trend assessment of the four
endangered fish species and for use as a contextual basis for determination of
recovery goals was deemed adequate only for Colorado pikeminnow and some
populations of humpback chub. Colorado pikeminnow is well distributed in the
Upper Basin and population estimates for the Green, Yampa, White, and Colorado
rivers appear stable or increasing. These trends are corroborated by catch per
unit effort data collected through standardized monitoring. The Green and
Colorado rivers support larger populations than the tributary Yampa and White
Rivers. Passage and augmentation stocking may improve the distribution and
abundance of the Colorado pikeminnow in the Gunnison and San Juan Rivers.
Recruitment rates for the Green and Colorado river populations of Colorado
pikeminnow demonstrated decreasing trends, but were not considered causes for
concern given the magnitude and trend observed in abundance estimates.
Recruitment rates for pikeminnow populations in the Yampa and White rivers
appeared variable, but no declining trends were apparent. Length frequency
distributions for the Green, Yampa, White, and Colorado River populations reflect
the influence of variable year class strength annually, but appear stable in their
overall size structures with neither lack of recruitment or progressive loss of adults
evident in the distributions.

Population-level data were considered adequate only for Black Rocks and
Westwater Canyon populations of humpback chub in the Colorado River.
Population estimates from other studies were available for Black Rocks,
Westwater Canyon, Little Colorado River, Colorado River in Grand Canyon,
Yampa Canyon, Cataract Canyon, and Desolation-Gray Canyon. At the time of
federal listing, only two humpback chub populations were documented, and were
located in the Grand Canyon of the Colorado River and Hideout Canyon in the
Flaming Gorge basin of the Green River. Both were threatened by major dam
construction. Presently, six populations are known to exist in approximately 68%
of their historic habitat. Interpretation of trends using independent population
estimates for the Black Rocks and Westwater Canyon populations are not clear,
but the former population appears stable and a declining trend is possible for the
latter population though abundance remains substantial. Both length frequency
distributions and annual recruitment rates appear stable for both the Black Rocks
and Westwater Canyon populations. Populations of humpback chub have
persisted in all of the known locations since their initial discovery.

The status of razorback sucker and bony tail are clearly endangered. The
information available for razorback sucker demonstrates only one wild population
remains in the middle Green River and recruitment is inadequate to offset a
declining trend in abundance. A relatively large population in Lake Mojave is
maintained by augmentation stocking. Bony tail is functionally extinct in the wild,
and is represented almost entirely by captive broodstock. Available historic data