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 27

1.0

0.1
0.07

p(1)

0.01
.001 .01 .1

1

1 0

Nm

Figure A.I Relationship between proportion of private alleles and number of
immigrants per generation, assuming an island model of migration. From Slatkin
(1985).

In order to obtain an accurate estimate of Nm one needs to have at least 3 to 5
separate populations containing approximately equal, known numbers (=N) of
reproducing adults. For the Colorado squawflsh we could perhaps assume 5
populations of 500 reproducing adults each, bearing in mind that the uncertainty
regarding population size will be one source of error.
Twenty or more private alleles are required for the estimate, the number of
individuals from each population and the number of loci from each individual
necessary to achieve this will depend upon the mutation rate. With higher mutation
rates fewer individuals and loci will be needed (also, to sample more loci fewer
individuals would be required and vice~versa)

One problem is that the pattern of gene flow within the Colorado squawfish is
uncertain. If downstream larval dispersal is followed by movement up a random
reach, then the application of an island model of migration may be justified. If,
however, individuals generally return to their natal area and gene flow only comes
about by the occasional stray adult, most likely to end up in an adjacent population,
the migration pattern will be more one dimensional (see Figure A.2).