8117

• UCREFRP Catalog Number: 8117
• Author: Modde, T. and G. Smith.
• Title: Flow Recommendations for Endangered Fishes in the Yampa River.
• USFW Year: 1995.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

The Yampa River drains approximately 7,600 square miles and provides an
average annual flow of 1.2 million acre feet of water per year, of which about 28% is
contributed by the Little Snake River (Tyus and Karp 1989). Due to the lack of large
storage capacity, the Yampa River has a relatively natural hydrograph (Figure 2).
Flows in the Yampa River generally begin increasing in March from melting snow pack
and remain high through July (Figure 2). Mean flow during spring runoff in the Yampa
River is about 5,403 cfs (U.S.G.S. flow records). River discharge may widely fluctuate
during spring runoff due to local warming trends and rain events. A maximum
discharge of 33,200 cfs was recorded 18 May 1984 at Deerlodge Park (Ugland et at.
1987). The 50% exceedance for daily peak spring flows in the Yampa River at
Deerlodge Park is about 13,738 cfs (U.S.G.S flow records). Following spring high
flows the discharge of the Yampa River declines to approximately 359 cfs (50%
exceedance of historic flows, U.S.G.S flow records) between the months of August
and February. Despite having a natural hydrograph, the average annual water
depletion of the Yampa River was estimated to be 110,000 ac ft in 1989 (~ydrosphere
" 1995a), with a disproportionate quantity depleted during the baseflow months. In
addition to water flow, the Yampa River also transports on average 1.5 to 2.0 million
tons of sediment per year, much of which is delivered by the Little Snake River which
drains both northwest Colorado and southwest Wyoming (O'Brien 1984).

Biological Background

Colorado squawfish, humpback chub, bonytail, and razorback sucker were
once common throughout the Upper Colorado River Basin (Quartarone 1993). All four
species are currently listed as endangered species by the U.s. Fish and Wildlife
Service. Previous to systematic studies initiated after the Green River rotenone effort
(Holden 1991) in 1963, abundance and distribution of endangered fishes was based
largely on anecdotal information (Tyus 1991). Studies following the closure of Flaming
Gorge Dam reported an absence of native fishes in the Green River above the
confluence of the Yampa River which was thought to be due to changes in water
temperature resulting from hypolimnetic releases from Flaming Gorge Dam (Vanicek
1967, Vanicek et at. 1970). These studies reported that native fish habitat was
maintained below the confluence of the Yampa River, a presumed consequence of the
Yampa Rivers' ameliorating effect on water temperature.

All fishes indigenous to the potamon section (Le. warm water region) of the
Yampa River, with the possible exception of bonytail, persist today despite the
introduction of at least 18 nonnative fish species (Tyus and Karp 1989). lri this
decade, Colorado squawfish, humpback chub and razorback sucker have been
collected in the Yampa River (unpUblished data, USFWS). All three species spawn in
the Yampa River and reproduction is closely associated with changes in the
hydrograph (Tyus and Karp 1989). One of the two largest known concentrations of
spawning Colorado squawfish occurs between RM 15 and RM 30 (Tyus and Karp
1989). In addition, one of two documented spawning aggregations of razorback
sucker in the Upper Colorado River Basin occurs at the mouth of the Yampa River,
just above its confluence with the Green River, the other is located approximately 34

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