8249

• UCREFRP Catalog Number: 8249
• Author: Modde, T., W. J. Miller and R. Anderson.
• Title: Determination of Habitat Availability, Habitat Use, and Flow Needs of Endangered Fished in the Yampa River Between August and October.
• USFW Year: 1999.
• USFW - Doc Type: Project #CAP-9,
• Copyright Material: NO

agricultural land. Only a small percentage of the riverbank is stabilized by shrubby vegetation and bank
erosion is common. The Maybell gage is located near the upper edge of this stratum at RM 85.8.

Stratum 8 extends from RM 91.6 to RM 135 at the town of Craig, Colorado. In this stratum the valley
tends to be more confined than in Stratum 6. Between RM 91.6 and RM 105.0 the valley is wide enough
for hay fields and pastures adjacent to the river. The river reach between RM 105 and RM 126 is the
Bureau of Land Management (BLM) Little Yampa Canyon Management Unit. Most of the river bottom
in this reach is owned by the BLM. The canyon walls are not as confined as Yampa Canyon and a flood
plain is typically associated with at least one side of the river.

Description ofYampa River Biotic System
The influence of seasonal changes in hydrology on movement and reproduction of large river fishes in the
Upper Colorado River Basin is well documented (e.g. Tyus and Karp 1989, Stanford 1994). Hydrology is
important in initiating movement to spawning areas (Nesler et al. 1988, Tyus 1990, Karp and Tyus 1990,
Modde and Irving 1998) and determining both the formation (Ligon et at 1995, Rakowski 1997) and
availability (Orchard and Schmidt 1998) of habitat for fishes in large rivers. Much of our knowledge of
hydrological effects on fish in the Colorado River Basin are linked to responses from high and receding
flows on fish and habitat (Stanford 1994). Relatively little is known about the importance oflow flows to
the maintenance of native fishes in southwestern rivers.

Several studies have shown that native fishes tolerate higher flow events than nonnative fishes in arid
streams and rivers in the southwest (Meffe and Minckley 1987, Minckley and Meffe 1987, Deacon 1988,
Hoffnagle et al. In review, Muth and Nesler 1993). Hawkins and Nesler (1991) reported that nonnative
fishes declined following years with high spring discharge in the Upper Colorado River Basin. In
general, fishes native to the southwest have shown a greater tolerance to environmental variabil~ty. Given
that native fish tolerate a more highly variable flow regime, seasonal as well as annual variability was an
important element in the modified flow recommendation for the Yampa River by Modde and Smith
(1995). Poff et al. (1997) suggested that the natural flow regime of all rivers is inherently variable and
that this variability is critical to ecosystem function and native biodiversity. Studies in Midwestern (Poff
and Allan 1995), Californian (Baltz and Moyle 1993), and Australian streams (Closs and Lake 1996) have
suggested that maintaining natural flows regimes, including baseflow variation, is important in
maintaining native fish assemblages. This rationale suggests that if environmental variation is reduced,
dominant nonnative species could displace or eliminate tolerant, less competitive native species. Because
abiotic factors are more influential on ecological processes in highly variable systems such as the Yampa

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