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

Squawfish Population Viability Analysis --July 1993

Page 34

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Population Size at Time t

Figure 3.3. A population model that shows an Allee Effect (see text).

This kind of Allee Effect could explain the relatively rapid extinction of
the squawfish in the lower and higher stretches of the Colorado River
system, though I argue below that spatial extension and changes of the adult
size distribution are confounding and contributing factors.

3.5 Adult Size Distributions and Population Fecundity

The distribution of adult fish sizes, based on the CRFP data (1400 records;
see the demography section, above) is shown in Figure 3.4. Anecdotal
evidence suggests that much larger adults existed during the early
exploitation of this fishery. The reason for this is simple. With lower
adult death rates, fish lived longer and achieved larger sizes.