7037

• UCREFRP Catalog Number: 7037
• Author: Wyoming Game and Fish Department
• Title: Fishery Research Report
• USFW Year: 1978.
• USFW - Doc Type: Flaming Gorge Reservoir.
• Copyright Material: NO

Whitefish, roundtail chubs, carp and mountain suckers have never
been abundant in the nets. That few carp are taken is not surprising
because of mesh size but catch rates have been similar for 14 years.
Carp appear seasonally abundant because they are easily seen in early
summer during peak spawning. The whitefish, roundtail chub and
mountain sucker are more common in streams (Baxter 1970) and
therefore, will probably never be abundant in Flaming Gorge.
Cutthroat and brown trout have not been common in the nets.
Cutthroat have been stocked irregularly and current stock is dependent
upon recruitment from tributaries in the canyon area. Brown trout are
stocked and increasing slowly in net catches.
Holcik and Pivnicka (op. cit.) discuss population shifts from primarily
phytophilous fishes (higher production) to indifferent fishes which
suppressed the earlier abundant fish. This process is noted as taking
about 10 years. Associated with the change was a dramatic decline in
growth rates of the previously abundant fishes. The changes at Flaming
Gorge over a similar period are related to planktivorous fish (rainbow
trout and Utah chub) versus the omnivorous white sucker. Utah chubs
and white suckers reproduce in the impoundment, are not subject to
fishing pressure, and are more efficient planktivores than trout.
Rainbow (as well as other Salmo) do not reproduce in the reservoir, are
fished heavily and apparently prefer larger zooplankton. Perhaps the
declines in trout stocks should have been more readily anticipated.
Trout growth does not appear to have been adversely affected by
rising populations of chubs and suckers; current age-growth data for
trout show virtually the same growth as described by Varley, Regenthal
and Wiley (1971) -- about 25 mm (one inch) increase per month. There
is indication that the decline in rainbow populations is attributable to
fishing presure, predator fishes (other large trout), as well as competition
with the more numerous Utah chub and white sucker. Growth of trout
may be affected with continued evolution of the reservoir assuming
current trends in population of non-game fish.
We have established that rainbow in Flaming Gorge feed primarily on
zooplankton throughout their life. Ivlev (1961) and others indicate
trout as primarily insectivorous and prefer food of the largest possible
size with morphological features imposing a limiting and optimum size.
Since rainbow in Flaming Gorge feed primarily on zooplankton in spite
of the abundance of forage fishes, we concluded that forage fishes are
either too large or not available to rainbow trout. Conversely, we have
established (Wiley and Varley 1971) that brown trout feed a good deal
on forage fish, primarily the Utah chub.
Changes in fish populations have varied by reservoir area; declines in
rainbow stock have been least in the canyon area and increases in
competing non-game fishes have been greatest in the open and inflow
areas. These areas are typified by extensive shallow water areas
necessary to production of non-game fishes. There is complete
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