9314

• UCREFRP Catalog Number: 9314
• Author: Wick, E. J. and J. A. Hawkins.
• Title: Colorado Squawfish Winter Habitat Study.
• USFW Year: 1989.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

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 encountered problems when the rate of
inbreeding was 1% or lower per generation. A maximum of 1% inbreeding rate is
recommended for wild populations (Simberloff 1988). The acceptability of the
"500" value was proposed for genetic drift based on a single trait in a fruit fly.
Both values of this "50/500" rule have been disputed and no magic numbers or
specific rules appear to be valid for propagation of animals (Simberloff 1988).
Inbreeding is of particular importance because it has been demonstrated that
inbreeding depression in brother-sister matings for some species will result in
offspring that are sterile or inviable after several generations (Lande 1988).
The l% maximum inbreeding rate (N =50) recommended by Simberloff (1988) for wild
populations should be used as a target for an effective population size in
developing broodstocks.
Allendorf (1993) recommended stocking equal numbers of offspring of family lots
from pedigreed matings. This practice will reduce the potential for loss of
genetic diversity. Philipp et al. (1993) recommended that genetic
characterization of captive-reared fish be compared with wild stocks to ensure
that the genetic diversity is similar.
I. Ideal Number of Founders for Broodstock Development. The designation of
"endangered" to any organism under the Endangered Species Act implies that the
numbers of wild organisms are limited. The basic goal in a captive propagation
program is to maintain the genetic diversity of captive broodstocks that is
similar to the parent wild stock. Simberloff (1988) emphasized that general
agreement does not exist about the absolute numbers of animals needed to maintain
genetic diversity in captive propagation programs.
To achieve Simberloff's recommendation of keeping the maximum rate of inbreeding
at 1% or lower, an effective population size of fifty parents (25 males and 25
females) is needed for development of a broodstock. Mating of one male with one
female is desirable to maximize the genetic contribution from all fish used as
parents (Allendorf 1993). This strategy of 25 paired matings is recommended as a
target for an effective population size in all captive propagation efforts. This.
strategy was designated as "Priority 1" in Box 10. The fertilized eggs from
mating one male and one female (i.e., 1 family lot) should be divided equally and
reared in separate facilities when ever possible to avoid the total loss of
genetic contribution through an accident or catastrophe.
If sufficient numbers of fish are in the wild, the goal would be to increase wild
recruitment until self-sustaining populations are realized to meet the carrying
capacity of available habitat. However, in declining fish stocks with little or
no recruitment, captive propagation may be necessary to augment wild stocks since
a critical level of abundance of adults or threshold density (Allee Effect) may be
needed for successful natural spawning Mande 1988). In river reaches where the
fish have been extirpated, restoration stocking will be necessary, provided that
suitable habitat is available for all life stages. In many cases, it will not be
possible to obtain an effective population size of 50 adults in one year. In
these instances, broodstock development can be accomplished over a number of years
by using paired matings and crossing year classes (Item 2 in Box 10).
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