7136

• UCREFRP Catalog Number: 7136
• Author: Johnson, J. E., et al.
• Title: Flaming Gorge Tailwater Fisheries Investigations
• USFW Year: 1987.
• USFW - Doc Type: Trout Growth, Harvest, Survival, and Microhabitat Selection in the Green River, Utah, 1978-82
• Copyright Material: NO

Trout Growth
In 1978, the penstock inlets of Flaming Gorge Reservoir were
modified to permit selective withdrawal of warmer, epilimnetic water from
the reservoir. As a result, growth of rainbow and cutthroat trout in the
tailwater increased to levels above those recorded any time prior to
1978. Annual growth increased approximately 3-fold over that measured in
1976. Consequently, trout fingerlings stocked at 100-125 mm (4-5 inches)
total length (TL) in May began contributing to the creel during their
first summer at large. In contrast, the 1976 year class of fingerlings,
stocked prior to the penstock modification, required two years in the
tailwater to reach a catchable size. Prior to the modification, growth
was fastest at Browns Park, the downstream extremity of the Utah
tailwater, and slowest at the dam. Following penstock modification,
growth had increased at all stations, but fastest growth was registered
at the tailrace.
The modification has, therefore, met the objectives for enhanced
trout growth set forth in the 1975 Environmental Assessment of the
penstock modification project. Growth is now comparable to that in other
productive western tailwaters, such as the Bighorn River below Yellowtail
Dam and the Beaverhead River below Clark Canyon Dam, Montana.
The increase in growth undoubtedly resulted from the direct effect
of the warmer water temperatures in summer on trout metabolic rate.
Other indirect mechanisms may also have been involved. Benthic
invertebrates, a major food for trout, increased in diversity and
abundance. Warmer temperatures, and the more natural synchronization of
temperature and photoperiod cycles, contributed to increases both in
macroinvertebrate biomass and species diversity.
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