CORVALLIS, Ore. - A 15-year analysis of spawning steelhead in one Oregon fishery has proven what many experts suspected for some time - that after fish from traditional hatcheries migrate to the ocean and return to spawn in natural habitat, they leave far fewer offspring than their wild relatives.
The study used DNA tracking technology of fish breeding in Hood River, and showed that traditional hatchery steelhead produced 60-90 percent fewer surviving adult offspring than wild steelhead.
However, the research also confirmed that fish from modern "supplementation" hatcheries, which begin with eggs from native, wild fish, are about as successful as wild steelhead. These fish can be used to boost the size of native populations without causing obvious genetic harm, at least for one generation.
The findings, by researchers from Oregon State University and the Oregon Department of Fish and Wildlife, were just published online in Conservation Biology, a professional journal.
"This provides very compelling data to confirm what we've suspected for quite a while, that fish from traditional hatchery operations have a much-reduced ability to reproduce and sustain a wild population," said Michael Blouin, an OSU associate professor of zoology.
"We've essentially created a fish version of white lab mice," Blouin said. "They are well-adapted to life in the hatchery, but do not perpetuate themselves in a wild environment as successfully as native-born fish. The good news, however, is that reducing the number of generations a stock is passed through the hatchery can greatly increase the fitness of that stock in its natural habitat."
The historic role of hatcheries was to produce fish for harvest, but a new mission for many hatcheries is to produce breeders to add to dwindling wild populations.
"Our work suggests that first-generation hatchery fish can be used to provide a significant one-time boost to a wild population without apparent damage to the genetics of the wild stock," Blouin said. "Whether you can continue that on a long-term basis is still unclear. But it seems that at least the first generation of fish produced this way function pretty well."
Traditional steelhead and salmon hatcheries in Oregon, Blouin said, usually worked with non-native fish that were repeatedly - and purposefully - bred for generations in hatcheries. The offspring of hatchery fish actually made better "domesticated" fish in the hatchery environment, he said, where inadvertent selection for traits like a less aggressive temperament produced stocks that had high egg-to-smolt survival in the hatchery.
However, the genetic characteristics that make good hatchery specimens work against the offspring of those fish when the offspring are born into a competitive and predatory wild environment.
The techniques used in supplementation hatcheries - use of local, wild-born fish for eggs - have been designed specifically to minimize those genetic effects of the hatchery. And it appears that at least on a short-term basis, Blouin said, they can achieve that goal.
To study the issue, researchers used "genetic fingerprinting" techniques to track the pedigrees of fish in Oregon's Hood River, doing DNA analysis with scales taken from about 15,000 fish since 1991. The relative reproductive success of wild fish and supplementation hatchery fish was compared to fish from traditional hatchery programs, by matching returning adult offspring to their parents that had spawned in the river in years past.
The study found that steelhead from traditional hatcheries had about 10-40 percent the reproductive success of wild fish. By contrast, fish from a supplementation hatchery had reproductive success indistinguishable from wild fish, and crosses between wild fish and supplementation hatchery fish also appeared healthy.
"By tracing the lineage of those fish, we've shown pretty clearly that fish from traditional hatcheries do not reproduce as successfully as wild fish, and thus could potentially drag down the health of wild populations by interbreeding with them," Blouin said. "But in places where we need a short-term boost to a wild population, it also appears that supplementation hatcheries may work well and not cause significant problems."
Although first-generation supplementation fish were as successful as wild fish, the researchers were hesitant to recommend supplementation as a long-term solution for dwindling wild runs.
"With many generations of supplementation you inevitably start using fish for broodstock that have hatchery ancestors," Blouin said. "Whether this results in enough domestication to cause problems down the road is still an open question. All we can say for now is that supplementation does not appear to be harmful in the short term."
The research considered only the genetic background and lineage of the fish, Blouin said, and did not take into account any other environmental or fishery management issues. If a stream or fishery environment is severely altered or degraded, he said, adding supplementation hatchery fish to the system will do little to achieve a self-sustaining wild population.
This research was supported by the Bonneville Power Administration and the Oregon Department of Fish and Wildlife.
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