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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operations as defined in section VI.

Releases For HUMPBACK CHUB Benefit Most Resources
But Could Reduce Trout Growth And Beach Area

A scenario which enhances the reproduction and suc-
cessful rearing of humpback chub is characterized by
flows at maximum powerplant capacity in May and June,
and steady flows .during the remainder of the year
(Figure VII-1). The high flows in May and June would
back up the Little Colorado River, creating a large
area of relatively warm, low-velocity flow which
appears to be beneficial to chub reproduction and lar-
val survival.

Providing releases which increase humpback chub numbers
may alsQ protect or enhance many of the other critical
resources compared to current dam operations. Common
native fish, for example, would not be subject to the
daily changes in backwater location and temperature
caused by fluctuating releases. Steady flows during
iate summer months would allow these fish to rear in a
low-velocity and relatively warm environment which may
enhance growth, minimize energy expenditure, and reduce
predation .risks compared to the current pattern of
fluctuating releases. Trout reproduction and trout
fishing may also benefit from this scenario compared to
current operations. Although high flows during May and
June reduce low-velocity habitat preferred by larval
trout, spawning would be successful because spawning
areas would not be exposed and adults would not be
stranded by fluctuating river levels. If numbers of
naturally spawned trout increased as a result, fish-
stocking could be decreased. However, trout growth
rates could decline due to the absence of fluctuating
flows, which increase food availability. (See Appendix
B, Section VII.)

Flow conditions for fishing and white-water boating
would be improved by elimination of fluctuations.
Boating safety would also improve because of the
elimination of flood releases and very low flows.

Operations modified for chub probably would be damaging
to beaches in the long term. Although floods would be
each year would result in greater sand transport than