8182

• UCREFRP Catalog Number: 8182
• Author: Bestgen, K. R. and L. W. Crist.
• Title: Response of the Green River Fish Community to Construction and Re-regulation of Flaming Gorge Dam. 1962-1996\
• USFW Year: 2000.
• Copyright Material: NO

Distribution and abundance ofnon-native fishes was uneven throughout the study area
from 1994 to 1996. The fewer coolwater species were relatively common in Browns Park, but
were uncommon in upper Lodore Canyon where native taxa dominated. Non-native species
tolerant of warm water dominated low velocity areas in lower Lodore Canyon, the Island and
Rainbow parks reach which began 18-km downstream of the Yampa River, and the lower Yampa
River. Potentially problematic piscivores, including northern pike, smalhnouth bass, and channel
catfish, have increased since 1980 and especially in lower Lodore Canyon. A strong longitudinal
water temperature gradient likely played a role in regulating distribution and abundance patterns
of fishes. Limited low velocity habitat in upper Lodore Canyon likely also restricted abundance
of red, sand, and redside shiners, and fathead minnow.
Several additional hybrid sucker combinations were detected relative to 1980 sampling
and comprised 7% of all suckers captured. Hybrids with white sucker as one parental type were
particularly common. Occurrence of cool water white suckers and their hybrids declined in a
downstream direction in Lodore Canyon, presumably in response to warmer water temperatures.
Summer water temperatures of the Green River from upper Browns Park downstream to
lower Lodore Canyon were reliably predicted by empirical regression models using air
temperature and discharge as independent variables. Water temperatures suitable for Colorado
pikeminnow reproduction were available in early summer in some years, but mid- and late-
summer temperatures were depressed due to increased discharge from Flaming Gorge Dam.
Increased discharge was mandated by the 1992 Biological Opinion on operation of the dam.
Further restoration of the fish community and habitat in the regulated reach of the Green
River requires discharge and temperature patterns more similar to the unregulated Yampa River
and the pre-dam Green River. Such patterns may promote growth and reproduction by rare
Colorado pikeminnow in Lodore Canyon and may also benefit native fishes in less-regulated
reaches downstream of the Yampa River. Distribution and abundance ofnon-native fish
populations will also likely expand if summer water temperatures of the regulated reach of the
Green River are enhanced.
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