7423

• UCREFRP Catalog Number: 7423
• Author: U.S. Bureau of Reclamation.
• Title: Glen Canyon Environmental Studies Draft Report, September 1987.
• USFW Year: 1987.
• USFW - Doc Type: Washington, D.C.
• Copyright Material: NO

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Non-operational Approaches May Also Enhance Or
Protect Downstream Resources

Several
impacts
natives
positive
known.

non-operational alternatives could offset
to downstream resources. Although these alter-
have not been systematically evaluated,
and negative aspects are described where

Trout reproduction. The need for minimum releases
during the winter to protect trout spawning beds and to
reduce stranding of adult fishes can be relaxed by in-
creased stocking with hatchery fish. Increasing the
stock of fingerling trout could minimize the impact of
losses in the natural population under fluctuating
flows. Supplemental stocking might eliminate the ap-
parent conflict between the fluctuating flows required
for trout growth and the steady.flows needed to protect
natural reproduction. The number of fish required for
stocking and the cost of such a program have not been
determined. Further, the loss of naturally produced
rainbow trout may adversely affect the quality of the
fishing experience for some anglers who prefer to catch
"wild" fish (Appendix C, Section IV.)

Humpback chub and common native fishes. If water
temperature in the mainstem were increased to 62
degrees F during May and June, chub might expand their
spawning area into the mainstem Colorado River,
reducing their dependence on a relatively small area of
habitat in the Little Colorado River. In addition,
increased water temperature could allow reintroduction
of endangered fish species, such as the Colorado
squawfish, that were lost to the river after construc-
tion of th~ dam.

Warming of tailwater releases through the summer period
would also enhance growth of native fishes and trout.
In addition, increased water temperature would increase
the availability of low-velocity, warm-water habitats
required for rearing of larval common native fishes and
possibly reduce their current dependence on backwaters.
The only practical way to increase temperatures over
several months, given the changing elevations of Lake
Powell, is to modify the dam intake structure to allow
intake of warmer water nearer the surface of the reser-
voir.

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