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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no evidence or suggestion that the Colorado squawflsh does
not have a density-regulated carrying capacity. This K value is
doubtless shifted below the level that prevailed before human
disturbance.

Positive density dependence and partially correlated spatial
connectance are the key findings that support the conclusion
of high viability. The final computer model of the Upper Basin
showed no extinction over substantial spans of parameter
values.

Vulnerability is a more difficult issue than viability. I
speculated that an Allee Effect, based upon the spawning size
of adults, could upset positive density dependence. And I
argued that any major externally imposed fragmentation, i.e.,
along the first 150 miles of the Green River, would destroy
both density regulation (recruitment) and the buffering
source/Sink rescue effects. This, I argued, could cause the
extinction of the entire system. Through lack of data, I was
unable to speculate on vulnerabilities associated with the
juvenile stages. And, through both lack of data and lack of
understanding, I was unable to speculate on, vulnerability
associated with major flow modifications.