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

Poff and Ward (1990) suggested that in highly variable/unpredictable flow
regimes abiotic factors dictate ecological processes, whereas, under more benign or
predictable flow regimes biotic factors such as competition or predation are more
influential. In this respect, species adaptable to variable environments will persist in
the face of environmental heterogeneity and disturbance, whereas, others (Le.
nonnative species) may colonize but will not persist. Conversely, under moderated
conditions biotic interactions become more determinate and nonnative species have a
greater opportunity to persist. In California streams, Baltz and Moyle (1993) stated
that the maintenance of native fish assemblages required maintaining natural flow
patterns which included the high winter floods and the low summer baseflows.

Several studies support the concept that flow variation is important to the
maintenance of native fishes in western rivers and streams (e.g. Hawkins and Nesler
1991, Baltz and Moyle 1993, Minckley and Meffe 1987). Much of this literature relates
to the importance of peak flows to the persistence of native species. Ind~d, peak
flows seem to be the dominant factors influencing spawning migration, spaWning,
larval transport to nursery sites and adult habitat in the Yampa River (fyus and Karp
1989). Very little information exists relative to the importance of baseflows on native
fish communities. Although some studies have indicated the importance of baseflows
to native species in intermittent streams (Deacon 1988, Paloumpis 1958), these
studies are not applicable to the permanent flowing Yampa River. Poff and Allan
(1995) evaluated fish assemblages in various flow regimes in midwestern streams and
rivers and concluded that fluctuations in baseflow can influence persistence among
ftshes.

Data clearly demonstrate the relationship of natural flow patterns to the
biology of endangered fishes in the Yampa River (Tyus and Karp 1989), however, the
quantity of flows and variation necessary to maintain rare native species within and
among years has not been experimentally defined. Although correlations of fish
declines with changes in the hydrograph have been demonstrated (e.g. Walker and
Thoms 19Q.3, Modde et al. accepted for publication) the specific causal factors
associated with native fish declines have not been clearly demonstrated. Nonetheless,
the dependence of native fish assemblages on a variable hydrograph have been
clearly demonstrated in arid landscape rivers and streams. As discussed by Stanford
(1994), no universal quantitative method of determining specific habitat needs (Le. flow
recommendations) of fishes exists and an adaptive management approach using the
best information available represents the most desirable approach. Stanford (1994)
further recommended that, due to the "critical" nature of flows and habitat in the
Yampa River, and its importance to the recovery of endangered fishes in the Upper
Colorado River Basin, the U.S. Fish and Wildlife Service interim flows should be
adopted and evaluated. However, Stanford (1994) cautioned that the environmental
baseline needed to be revised and that flow recommendations not be based on
monthly averages because of the need to incorporate instantaneous variation which
was a "very important component of river ecology".

26