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 22

(see the preceding demographic analysis). With adult population size
greater than 1000 (cf. Tyus 1991) and only 10 or so generations since
western man began significantly to disturb the system, the expected loss of
heterozygosity through drift is miniscule. Based on these numbers it is

Ht=lO =

(l-(1/(2 * 1000))) 10

=

.999510

= .995,

or a 0.5% loss. Accepting the 5% H value of Ammerman and Morizot
(1989), the year 1800 value would have been 5.025%.

2.7 Selection on the Colorado Squawfish

Selection is a different matter. There is perhaps no other endangered
species living is such an altered environment. The Colorado squawfish
now experiences different water flow regimes, a different prey base,
different competitors and predators on the its juvenile stage, different
limits to its migration. Assuming some genetically based variation in traits
involved with these various interfaces to its environment, the Colorado
squawfish is almost certainly evolving "better" adaptations to its new
environment. If this selection were solely on the juveniles and acted in a
"soft" manner, i.e., not affecting A, then this evolution could be quite
rapid. However, this is not likely to be the case, and the Colorado
squawfish will probably remain maladapted to its current environment for
centuries.

It would have been extremely valuable if Powell and the early explorers of
the Colorado basin had done a thorough genetic sample of the Colorado
squawfish. Sadly, their government funding had a different focus.
Without a 'before' baseline, it is impossible to quantify genetic change.
Possibly, museum samples could be assayed, but this would only go back a
few generations.

2.8 Are There Genetic Subunits?

The Colorado squawfish has already gone extinct in v~ous upper reaches
(above dams) and the lowest reaches of its range (below Lake Powell). It
is extremely unlikely that the current distribution, centered on the Green
River (see Figure 2.2), will show genetic differentiation. This figure is
based on CRFP data from 1978-1989 (supplied by Chuck McAda) and also
on independent data for the same time period for the Colorado river from
Moab to just beyond Grand Junction (also supplied in tabular form by
Chuck McAda). These numbers represent all subadult and adult Colorado