Researcher's Model says Hatcheries Select
by Bill Bakke
Using hatcheries to recover wild salmon by supplementing their numbers with artificially propagated fish has become the new solution for saving salmon on the West Coast, but a NMFS researcher has developed a model that shows there may be fundamental problems with this approach. Michael Ford's paper in Conservation Biology (Vol. 16, No. 3, 815-825) says the strategy may not work even if wild fish are constantly introduced into the hatchery environment.
"I explicitly explored this two-population scenario," says Ford, "and found that substantial phenotypic changes (changes in behavior characteristics such as run timing, distribution and courtship) and fitness (survival) reductions can occur even if a large fraction of the captive broodstock is brought in from the wild every generation. This suggests that regularly bringing wild-origin broodstock into captive breeding populations cannot be relied upon to eliminate the effects of inadvertent domestication selection."
However, Ford pointed out that the rate and level of domestication will be reduced compared with hatcheries that operate as completely closed systems, relying only upon a returning hatchery stock for breeders.
He said there are two interesting implications to this finding. "First, it means that wild-origin breeders are important to a population's viability in the wild even in cases where the wild population is not able to sustain itself without the aid of supportive breeding." And he found that "the dependence on the potential reproductive rate in the wild environment means that conserving or restoring a population's habitat (or addressing other factors that limit the population's reproductive rate) may be the most effective method of preventing phenotypic change during supportive breeding."
Ford's model explored scenarios of fish populations that had reproductive rates below replacement, which means the wild salmon would go extinct without supportive breeding supplied by a hatchery. He said that it is important to control the rate of exchange between hatchery and wild populations in order to limit domestication of wild populations. He noted that in situations where hatchery fish are used to support a wild population, it may be impossible to actually keep the hatchery fish numbers low. Given enough time, hatchery fish could then transform a wild population by changing the phenotypic characteristics important to its survival in nature. Ford said one could expect "phenotypic changes and fitness loss in wild populations even at low rates of introgression.
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