7989

• UCREFRP Catalog Number: 7989
• Author: Crowl, T. A. and N. W. Bouwes.
• Title: Modeling Population Dynamics of Colorado Squawfish, Razorback Sucker, and Humpback Chub
• USFW Year: 1997.
• USFW - Doc Type: for Management Objective Development.
• Copyright Material: NO

The U~oer Basin Colorado River Context
We modeled the population dynamics of the four endangered fish species in the Upper
Basin of the Colorado River to determine current patterns of population dynamics, both
temporally and spatially, as well as predictions for numbers of fish required or changes
in demographic parameters necessary to fulfill management targets specified by Upper
Basin Researchers (see UDWR report regarding Management Objectives). Target
species included the Colorado squawfish (Ptychocheilus lucius), the Razorback sucker
(Xvrauchen to anus), the Humpback chub ( ' a c ha) and the Bonytail chub ( ila
I ans). We began by construction a Lotka-Volterra population model (see model
development section below) based on our general knowledge of the Upper Basin. The
model was constructed so as to be as specific as data would allow including spatial
delineation at the geomorphic reach and subpopulation scales. The original, generic
model included simple demographic parameters such as fecundity, sex ratio, and
survivorship values for YOY, 1-, 2-, and 3-yr old fish and adults.
Following the initial model development, a workshop was held at Utah State University
to discuss model structure, especially the spatial components of the river itself and the
subpopulations of Colorado squawfish. Figure 1 and Table 1 represent the overall
model structure agreed to and the geomorphic basis for the finest spatial structure that
was ultimately used for the model.
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