7742

• UCREFRP Catalog Number: 7742
• Author: Gilpin, M.
• Title: A Population Viability Analysis of the Colorado Squawfish in the Upper Colorado River Basin
• USFW Year: 1993.
• USFW - Doc Type: A Report to the United States Fish and Wildlife Service, Denver, Colorado.
• Copyright Material: NO

Table of Contents

Executive Summary.......................................................... page 1
Demography... ............... ................... ............................... page 3
Genetics........................................................................... page 18
Density Regulation............................................................ page 28
Spatial Dynamics............................................................... page 39
A PV A Model................................................................... page 43
Acknowledgements............................................................ page 43
References........ .............. ......... .............. ................... ........ page 44
Appendix: Comments and Reaction to First Draft Reviews..... page 46

-- Executive Summary --

I carned out a population viability analysis of the Colorado
squawfish in the Upper Basin of the Colorado River. The
analysis involved rather comprehensive but poorly focused
and incomplete data. Because of this, the PVA cannot be
offered as a proven collection of scientific hypotheses. A
number of different kinds of models were built, some partial
and one comprehensive. The first question asked (but the last
answered) was about the spatial connectivity of the system.
The second question asked was about the expected time to
extinction of the units of the system. The system of the Green
River, the White River, the Yampa River, the Colorado River and
other smaller rivers in the Upper Basin were judged to be a
connected whole that exhibits source/sink dynamics. The
expected time to extinction, based on the somewhat crude but
comprehensive final model, of this total system was computed
to be very long. That is, based upon the understanding
embodied by this analysis and the assumption that the
patterns seen in the data over the last decade will persist, the
Colorado squawfish is viable.

I looked for fragmentation, either in the spatial background or
in the population distribution itself, and the possibility of
metapopulation dynamics, as these are features and
properties I have successfully modeled with other endangered
species. There is no externally imposed fragmentation in the
Upper Basin (other than the major upstream reservoirs
already in place on the Colorado, Gunnison, Green and Yampa
Rivers). And I found no evidence for population fragmentation