7801

• UCREFRP Catalog Number: 7801
• Author: Valdez, R. A.
• Title: Synthesis of Winter Investigations of Endangered Fish in the Green River Below Flaming Gorge Dam.
• USFW Year: 1995.
• USFW - Doc Type: \
• Copyright Material: NO

Winter 2 with low flow). The Yampa River was ice-covered from early December to early March
of both winters.
The ten Green River fish in Winter 1 (ice-&ee conditions) were observed in runs, slackwaters,
eddies, and backwaters for 43, 39, 12, and 6 percent, respectively, of the time observed with
radiotelemetry. In Winter 2, nine different Green River fish in ice-free conditions were observed in
runs, slackwaters, backwaters, and eddies for 64, 29, 5 and 2 percent, respectively, of the time. The
same nine fish in ice-covered conditions occupied runs, backwaters, and slackwaters for 69, 17, and
14 percent, respectively, of the time observed. Greater use of runs in ice-free conditions in Winter
2 was attributed to lower main channel velocities from lower river flows. Greater use of backwaters
under ice in Winter 2 was attributed to greater availability of these off-channel habitats and use of
ice as cover by foraging fish.
Valdez and Masslich (1989) hypothesized that use of these habitats reflected resting and
feeding activities. Overwintering adult Colorado squawfish appeared to rest in slow midchannel runs
and slackwaters, and fed in eddies and backwaters. Increased use of backwaters under ice-covered
conditions in Winter 2 indicated use of ice as cover during foraging.
The Green River fish used habitats with low average channel velocity of 0.0 to 0.3 m/sec and
average depth of 0.75 to 1.35 m (Table 4). Fish in midchannel runs were commonly in deep sand
troughs, while fish in slackwaters were immediately downstream of sand shoals, at the base of steep
sand banks. Fish in rocky areas remained in eddies behind rock jetties, but did not use talus or
nearby vegetated shorelines (primarily tamarisk).
The Yampa River fish also used distinctly different ovecwintering habitat in the two years
observed. During Winter 1, the fish most often used off-channel habitats (i.e., backwaters and
embayments), while the fish in Winter 2 used primarily main-channel habitats (runs, eddies, and
pools). The difference was attributed to flows higher than the historic mean in Winter 1 and lower
that the historic mean in Winter 2 (Figure 11). High use of pool habitat in Winter 2 was also
attributed to incorporation of spool-dominated reach (Lily Park) into the study area in the second
year of the study.
The Yampa River fish seemed to use habitat according to availability. When a variety of
habitats was available--during high .flows in Winter 1--fish selected off-channel habitats over main
channel types. In Winter 2--whea flow was low--many off-channel habitats were desiccated or ice-
filled and not available to the fish. Wick and Hawkins (1989) noted that the fish used eddies and
pools in areas devoid of backwaters and embayments, such as at Lily Park But, in areas with a
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