7890

• UCREFRP Catalog Number: 7890
• Author: U.S. Fish and Wildlife Service.
• Title: Region 6, Fish and Wildlife Service Guidelines Directing Captive Propagation Of Listed And Candidate Fish.
• USFW Year: 1996.
• USFW - Doc Type: \
• Copyright Material: NO

It has been suggested that a population size of 50 is required to prevent
inbreeding depression (Soule 1980), and a 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 1% 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.
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 genetic diversity of captive broodstocks similar to 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
minimum target for an effective population size in all captive propagation efforts
(designated as "Priority 1" in Box 10). The fertilized eggs from mating one male
and one female (i.e., one family lot) should be divided equally and reared in
separate facilities whenever possible to avoid total loss of genetic contribution
from an accident or catastrophe.
If sufficient numbers of fish exist 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 (Lande 1988). In river
reaches where 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, broodstocks can be developed over a number of years by
using paired matings and crossing year classes (Box 10).
J. Breeding Strategy for Captive Propagation when Small Numbers of Fish are
I* - Available. If the number of available adult wild fish is low, mating 5 males and
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