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

(flow/habitat relationship) can be accurately predicted using hydraulic simulation models (Bovee 1982).
However, due to several concerns related to estimation of suitability curves (i.e., few observations, life
stage dependency, concerns regarding whether observations truly reflect suitable habitat [Tyus 1992], and
other criticisms of the PHABSIM approach [Stanford 1994], etc.), the primary means for determining the
impacts of low flows was based on estimates of change in river channel characteristics (curve break
analysis). In our approach, the use of weighted useable areas estimates for RHABSIM was used only as a
comparison to the stream profile approach.

The curve break analysis is a threshold approach using hydraulic simulation that was used to estimate
channel characteristics (mesohabitat availability) at various baseflow scenarios. The application of this
approach assumes that the Yampa River channel is in equilibrium. Telemetry data was used to identify
which mesohabitat types (runs, riffles, or pools) were important to Colorado pikeminnow Ptychocheilus
lucius and humpback chub Gila cypha. In addition, riffles were emphasized in the analysis because of
their importance to invertebrate production (Brown and Brussock 1991) as well as habitat use (as
discussed in Chapter 4). Guidance from the RIP expert panel (Drs. Stephen Ross, University of Southern
Mississippi; Robert White, Montana Cooperative Fish and Wildlife Research Unit, and William Trush,
McBain and Trush, Inc. and Humboldt State University) during two meetings in March 1997 and January
1998 emphasized the importance of riffles in the analysis because they are the most sensitive mesohabitat
to reductions in discharge. The curve break analysis was used to define the flow below which the greatest
loss in habitat availability occurred for each mesohabitat type (i.e. maximum degradation in stream profile
of the mesohabitat type). The rationale behind the curve break analysis is: 1) native fishes, including
listed species, in the Yampa River are adapted to local channel characteristics as they have existed
historically, and 2) that baseflows below the curve break flow represent the greatest loss of habitat and is,
therefore, detrimental to recovery of the fishes. However, because variability in low flows as well as high
flows is recognized as essential in maintaining native fish communities (Poff et al. 1997), we recognize
that endangered fishes have maintained persistent populations in the Yampa River despite periods of very
low flow. Therefore, the recommendation ofthis report is to maintain flows above levels that were
identified by habitat availability simulations integrated with an understanding of variability within the
context of the historical flow record.

The format for this report is set up by chapter to address the specific objectives ofthe study. This chapter
describes the purpose and approach taken in this study and the next chapter provides a description of the
hydrology and physical characteristics of the Yampa River study area. Chapter 3 presents analysis of the
physical characteristics of the Yampa River study area and provides simulations of channel features for

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