If conservation hatcheries are to operate to maximize
genetic diversity and population size while minimizing inbreeding when
introducing hatchery-bred salmon to wild stocks, some hatcheries may need to
alter their genetic management practices.
A recent review of conservation hatcheries provides a
summary of current and potential fish hatchery genetic management practices and
recommends strategies to guide management of conservation hatcheries in the
According to the study, published last month in the North
American Journal of Aquaculture, the overarching goal of a conservation
hatchery is to “prevent the extinction of threatened or endangered stocks by
enhancing natural production” and rebuilding the depleted stocks of fish, while
“minimizing the genetic impacts of releasing hatchery fish on wild
The study surveyed 36 hatchery programs. Some 28 of the
hatcheries were conservation hatcheries with stocks as far ranging as cutthroat
trout, chinook, coho, Atlantic and sockeye salmon, and steelhead.
Important goals for the conservation hatcheries, according
to survey results, are preserving the stock’s genetic diversity, managing for
effective population size, minimizing inbreeding and providing fish for
introduction into streams.
The survey found that one of the biggest differences between
non-conservation and conservation hatcheries is that non-conservation
hatcheries use random mating to both select and pair fish. Conservation
hatcheries, on the other hand, can use a variety of genetic methods.
“For small conservation hatcheries, we recommend genetic
management techniques that maintain genetic diversity, minimize inbreeding and
maintain effective population size, such as equalization of family sizes and
pedigree-based mean kinship selection,” said Kathleen Fisch, computational
biologist with the Center for Computational Biology and Bioinformatics at the
University of California, San Diego.
Not all conservation hatcheries are meeting all these
standards. Some 62 percent of conservation hatcheries use a random mating
scheme and single pair mating, but few track the pedigrees of the fish. Single
pair mating involves mating a single male with a single female.
“There have been several studies that demonstrate mate
selection in wild populations is non-random (although mating systems may differ
by species), so random mating in a hatchery likely does not mimic wild
reproduction, as you are eliminating mate choice and possibly mating related
individuals,” Fisch said.
Ideally, the report says, “full-sibling families should be
kept separate until individuals can be uniquely marked physically or genetic
marking can be implemented.”
Once that is done, a pedigree can be established, something
that even fewer of the hatcheries actually do (just five of the 36 hatcheries
reported have established pedigrees). Without the pedigrees, single pair mating
can result in the “reproductive potential of mates being linked to one
another,” the report says.
“Factorial mating” is recommended by a number of other
studies. It involves “crosses between all possible parents or matings of single
females to overlapping pairs of males,” the study says. Over half the
conservation hatcheries use this scheme. In one study cited, “partial and full
factorial mating were the most efficient mating schemes to preserve long-term
genetic variability and single-pair schemes were the least efficient.”
In fact, another study concluded that the scheme could
result in a 33 percent increase in the effective number of breeders over single
pair mating. However, full factorial mating is generally feasible only in small
populations, the survey concludes.
“Molecular relatedness” estimates can help hatchery managers
avoid mating siblings and can reduce the risk of inbreeding. Conservation
hatcheries that use molecular relatedness to develop breeding matrices, the
report says, includes Snake River Sockeye, listed as endangered under the
federal Endangered Species Act.
“In small populations, which by definition include almost all of those in conservation
hatcheries, avoiding full-sibling matings resulted in higher genetic diversity
in the hatchery only so long as the practice continued,” the study says. This
effect disappeared once the fish were introduced into the wild, however.
An important management scheme is equalization of family
size (EFS), in which each family contributes the same number of offspring to
the next generation. Methods for doing this include “culling the number of
offspring from each spawning pair, mating the same number of offspring to
produce the next generation, and releasing the same number of offspring from
each spawning pair into the wild to reduce the reproductive variance,” the
This is difficult, time-consuming and expensive, but some
conservation hatcheries are beginning to use EFS to “increase effective
population size in captivity,” the study says.
The report concludes that if a “manager aims to maximize
genetic diversity and effective population size and minimize adaptation to
captivity, this could be accomplished by starting with a large number of
founders, minimizing the number of generations in captivity, using locally
adapted stocks, employing factorial mating designs, and implementing procedures
to equalize family size.”
The study, “Fish Hatchery Genetic Management Techniques:
Integrating Theory with Implementation,” was published online June 19, 2015, in
the North American Journal of Aquaculture, http://www.tandfonline.com/doi/full/10.1080/15222055.2014.999846#.VaUl6_lViko.
In addition to Fisch, study authors include, Christine
Kozfkay, Idaho Department of Fish and Game; James Ivy, Collections Department,
San Diego Zoo Global; Oliver Ryder, Institution of Conservation Research, San
Diego Zoo Global; Robin Waples, NOAA Fisheries NW Fisheries Science Center,