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

River toward pre-dam conditions. It should be noted that fish community shifts detected during
sampling from 1994-1996 may be due to a combination of a delayed response of the fish
community to thermal modification in 1978, and changes in flow and temperature regimes since
1992. Colorado pikeminnow also increased in distribution and abundance, which may be
attributable to improved habitat conditions or to increased dispersal of individuals from
expanding populations in other portions of the basin. Distribution and abundance of cold water
rainbow and cutthroat trout has declined since 1980; brown trout, which are more tolerant of
warm water, are now relatively more abundant. Salmonids of any kind were quite rare in
lowermost Lodore Canyon in 1994-1996, whereas introduced warm water species such as red
and sand shiner, fathead minnow, and channel catfish have remained common or increased in
abundance since 1980. Increased summer water temperature that allowed reproduction by some
of these species may have been responsible for shifts in species composition.
Changes in the Lodore Canyon fish community between 1978-1980 and 1994-
1996.-Comparison of samples from sites in the upper and lower Lodore Canyon during 1978-
1980 (Holden and Crist 1981) with those taken from 1994-1996 showed decreased abundance of
cold water fishes, increased abundance of cool or warm water fishes, and increased abundance of
non-native fishes. Colorado pikeminnow increased in abundance at the lower Lodore site and
were first detected at the upper Lodore site in recent sampling. Reasons for the sharp decline in
speckled dace and the disappearance of mountain sucker at both sites were not obvious. Both
species generally inhabit riffles and runs with moderate to high current velocity, but that type of
habitat was not lacking in Lodore Canyon. Increased abundance of piscivorous brown trout in
upper Lodore Canyon may have contributed to reduced abundance of speckled dace.
Decreased relative abundance was noted at both sites for two Coldwater Salmonids,
rainbow and cutthroat trout, while brown trout and native mountain whitefish, which are tolerant
of warmer water, increased in abundance. Fathead minnow, redside shiner, and white sucker,
which were previously uncommon (Holden and Crist 1981), represented substantial portions of
the fish community at each site during 1994-1996; the latter two taxa were more abundant at the
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