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

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very important demographic variable. It modulates the stochastic variation
of gene frequencies (genetic drift). Demography also controls the
"memory" of a population. Only with a long-lived species can the
population "remember" past environmental events. That is, a good year
might produce a very numerous age class that will be recognizable in the
age/size structure of the population for years to follow. This is related to
the Storage Effect, considered later.

1.5 Different Historical Demographic Regimes

The Colorado squawfish has evolved as a top carnivore in a wild river
system. It's natural demography (pre-fishing by Homo sapiens) should
reflect these conditions, since this would be major part of its evolutionary
history. This natural regime was interrupted a few hundred years ago with
the entry of white man into the river basin. Until the last twenty-five
years, the Colorado squawfish was subject to an ever increasing harvest
pressure. Beginning in the 1930' s, the underlying stream ecology for the
Colorado squawfish was seriously altered with the construction of a series
of great dams. Almost simultaneously, the food web of the system was
widened and complicated by the introduction of exotic fishes that acted as
competitors and predators on juveniles, and possibly as prey. Most
recently, in 1974, the Colorado squawfish was declared endangered under
federal law, which certainly reduced the harvest pressure on the Colorado
squawfish.