8121

• UCREFRP Catalog Number: 8121
• Author: Williamson, J. H. and R. S. Wydoski.
• Title: Genetics Management Guidelines.
• USFW Year: 1994.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

Exact estimates of the effective population size are complicated. For
example, the formula given above for the effect of sex ratios assumes
random mating, constant population size through time, and variance in
fertility that approaches the Poisson distribution. Effective population
' size can be maximized by non-random matings of paired individuals and
equalizing the sizes of family lots (Allendorf 1993).

The effective population size should be maximized in every hatchery
generation to reduce the risk of loss of within-population genetic
variation (Kapuscinski et al. 1993). Strategies for conserving genetic
diversity in captive-reared endangered fish are summarized in Box 9.
Box 9. Strategies for conserving genetic diversity of endangered fish
in the Upper Colorado River Basin.
1. The genetic diversity of wild endangered fish stocks should be
characterized by genetic markers.
2. Captive propagation and stocking should be considered temporary
management tools to facilitate development of self-sustaining
wild endangered fish stocks.
3. Broodstocks should be developed from an appropriate donor source
in an artificial genetic refuge that offers maximum control.
4. Appropriate breeding strategies should be used to maintain genetic
diversity similar to the wild donor stock or population.
5. The genetic diversity of captive broodstocks and their progeny
will be monitored and compared to the genetic diversity of wild
stocks.
6. The number of captive-reared fish that are to be stocked should be
limited to prevent potential risks to severely depleted wild stocks
from genetic swamping.
The rate of inbreeding ( O F) can be calculated if the Ne is known using
the formula:
?F=
2 1 Ne
By applying this formula, the estimated rate of inbreeding for an
effective population size of 50 (equal sexes) is 1 %. For an effective
population size of 10 (equal sexes), the estimated rate of inbreeding
is 5%. Therefore, it is advantageous to use as many adult fish as
possible in developing broodstocks.
' It has been suggested that a minimum effective population size of 50 is
required to prevent inbreeding depression (Soule 1980) and a minimum
effective population size of 500 is required to reduce long-term genetic
' drift (Franklin 1980). The acceptability of the "50" value is empirical
from broad experience of animal breeders. Animal breeders have not
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