7023

• UCREFRP Catalog Number: 7023
• Author: Meffe, G. K.
• Title: Conservation Genetics and the Management of Endangered Fishes
• USFW Year: 1986
• USFW - Doc Type: Fisheries
• Copyright Material: YES

actions. For example, if an endangered fish retains viable
populations in both constant springs and fluctuating streams
(e.g., Vrijenhoek et al. 1985), the manager has a choice of
which gene pool to use for propagation, whether to combine
fish from both, or which gene pool to use for stocking a new
field site. Natural populations can be kept genetically iso-
lated, mixed and isolated captive stocks can be developed,
and gene pools used for introduction can be better matched
to the environment. It is therefore critical that variance among
naturally isolated populations, however subtle, be pre-
served and exploited through continued isolation wherever
possible.
Another problem in mixing naturally isolated demes is
potential loss of coadapted gene complexes (Dobzhansky
1970). This occurs when genes from one deme, which are
closely linked and "coadapted" to work well with one an-
other, are broken up by hybridization into gene complexes
that do not functior. together as well. It is quite common,
for example, for first generation hybrids to be robust, but
then to lose fitness over subsequent generations, presum-
ably as coadapted gene complexes are broken up (Rough-
garden 1979). Evidence for such "outbreeding depression"
is provided by Dobzhansky and Pavlovsky (1958) in fruit-
flies, Alstad and Edmunds (1983) in pineleaf scale insects,
and Stahl (1981) in Atlantic salmon (salmo salar). Rasmuson
(1981) pointed out the need for further understanding of the
importance of outcrossing to locally adapted gene complexes
in fishes. At present, it appears that the potential exists for
fitness reductions in fishes due to loss of coadapted gene
complexes.
In addition to mixing of naturally isolated groups, be-
tween-population variation can be lost through "convergent
selection," that is, common artificial selective forces in
hatcheries or modified natural habitats. If fishes from phys-
ically, chemically, or biotically different field sites are raised
in common hatchery environments, the same artificial se-
lective regimes will be applied to all. If this continues for
several generations, or if the forces are strong, the practice
has the potential of selecting for a common hatchery stock
and thus eliminating between-stock variation. Such con-
vergence in Atlantic salmon was documented by Stahl (1983).
Similar results may be obtained if differing natural habitats
are altered in the same ways, introducing new and common
selective forces.
Alternatively, formerly widespread, contiguous popula-
tions that have been separated by man into isolated demes
suddenly face the genetic problems of small populations
outlined above. In this case, supplemental gene flow by man
among these artificially isolated groups may be necessary to
maintain a larger Ne in each deme and thus "genetically
mimic" the natural situation. In this case, continued isola-
tion is not desirable, since the demes were large gene pools
until man's intervention.
Options For Managing
Endangered Fishes
Synthesis of the above information allows development
of management plans that minimize genetic damage and
maximize chances of long-term genetic health of small pop-
ulations (Table 1). Perhaps the most important step toward
sound genetic management is collection of data on popu-
Table 1: Recommended actions to maximize long-term genetic health
of endangered fishes
1. Monitor genetics of field and captive populations.
2. Maintain largest feasible genetically effective popula
tion size of captive stocks.
Effects:
Reduces erosion of quantitative variation.
Reduces loss of rare alleles.
Reduces inbreeding potential.
3. In small captive populations, avoid inbreeding through
selective mating.
4. Keep stocks in hatchery environments for as short a time
as possible.
Effects:
Reduces the several types of artificial selection.
Reduces "domestication."
Minimizes chances of bottlenecks, drift, inbreeding,
and catastrophic loss of the stock.
5. Maintain separate stocks of distinct populations to pre-
serve among-population variance.
lation structure and genetic and morphological variation (AI-
lendorf and Phelps 1981; Ryman 1981; Hamrick 1983). With-
out these data, we can only make blind decisions regarding
preservation of genetic variation. This was recognized in the
FAO/UNEP report of 1981 (p. 11), which stated "A good
knowledge of the population structure in the management
of fisheries cannot be exaggerated ... Only when stocks
are properly defined can the fishery be managed optimally."
They also emphasized (p. 11) that "When re-introduction
of a locally extinct population is contemplated, earlier base-
line information might allow a closer matching of the intro- duced fish to the original population. Proper genetic match- 4W,
ing would increase the likelihood of successful reintroduc-
tion ... Other things being equal, populations of maximum electrophoretic variation should be selected for introduction P?V!Ykl
-
because this probably increases the likelihood of evolution-
ary adaptation to a novel environment." Useful information t 2?
for such attempts would derive from electrophoretic and rrt??iN
chromosomal analyses, and morphometric and meristic
studies designed to obtain estimates of available intra- and
inter-population variation. Present examples include work
on western trouts (Behnke 1970, 1979), pupfishes (Turner
1973a, 1973b, 1974, 1984), and the Sonoran topminnow (Vri-
jenhoek et al., 1985).
Detailed genetic analyses should be conducted on any
endangered fish to determine how variation is distributed
within the species and how best to preserve that variation
(as per Chambers and Bayless 1983; Loveless and Hamrick
1984). In the case of aquatic organisms, it is convenient to
partition genetic variance into that contained within locali-
ties, between localities within drainage systems, and be-
tween drainage systems (Chambers 1980). Vrijenhoek et al.
(1985) conducted such an analysis on the endangered So-
noran topminnow (Poeciliopsis occidentalis) and found total
genetic variation in the species to be composed of diversity
within localities (21%), between localities within drainages
(26%) and between three major genetic groups, equivalent
to subspecies (53%). This analysis indicates it is vital to pre-
serve representatives of all three groups, and of somewhat
lesser importance (although not unimportant) to maintain