Study of Hood River Steelhead Finds Natural Selection in
by Scott Learn
Genetic adaptation of hatchery steelhead starts hurting spawning success within just one generation, according to a study of Hood River fish that could lead to pinning down the causes of hatchery domestication.
Classic Darwinian evolution is clearly at work -and it's working fast, the researchers concluded in their study, published today by the Proceedings of the National Academy of Sciences.
The findings confirm earlier suspicions and raise concerns about programs to supplement wild populations of salmon and steelhead by releasing young hatchery fish near spawning grounds. Unlike conventional hatcheries, supplementation programs try to integrate the hatchery populations into wild populations, many listed under the Endangered Species Act.
Earlier studies on the Hood River had already identified declining productivity in Hood River hatchery steelhead. The latest research shows it comes from domestication of young fish in hatcheries that can be passed on when hatchery fish breed with wild fish, not from a temporary environmental effect, said Mark Christie, an Oregon State University genetic researcher and the study's lead author.
"Now we know definitely that it's adaptation to captivity and it happens in a single generation, which is amazing from an evolutionary standpoint," Christie said.
Hood River steelhead that thrived in hatcheries had traits that were "beneficial in captivity but severely maladaptive in the wild," the study says.
Supporters of hatchery supplementation programs, including many Northwest tribes, caution against concluding that supplementation is bad. Tribes use it to help fulfill government promises made to sustain tribal fisheries when Columbia Basin dams were built and in treaties signed in the mid-1800s.
The productivity declines in Hood River steelhead are among the sharpest of many salmon and steelhead runs studied. And damage from dams and habitat destruction likely have bigger effects on productivity and returns, they say.
"It's important to remember that hatchery supplementation is a response to declining or depressed salmon populations, not the cause," said Peter Galbreath, a fishery scientist with the Columbia River Inter-Tribal Fish Commission. Supplementation is necessary "to rebuild populations at desired levels while we await, probably naively, rectification of the source problems," Galbreath added.
The tribes say they can manage hatcheries to reduce domestication problems, and have advocated doing so for two decades. Recent successes with Snake River fall chinook indicate carefully run programs can boost numbers of wild fish, they say.
The OSU researchers found that the hatchery fish that did best -- those who returned five or more siblings to wild spawning grounds -- showed a 71 percent decline in productivity after spawning in the wild compared to hatchery fish that returned fewer siblings.
Using hatchery fish as broodstock also resulted in far higher returns in the first generation than using wild fish eggs and sperm to stock the hatchery, the study found, another indication of rapid adaptation to captivity.
The findings clearly show that natural selection is fostering domestication of hatchery fish, said OSU Professor Michael Blouin, who also participated in the study.
It moves science a step closer to figuring out how to isolate what's going wrong in hatcheries and fix the problems, Blouin said. Blouin and other OSU researchers are studying that question now.
If crowded tanks prove to be a key problem, for example, hatcheries could reduce hatchery populations or build more tanks.
"In my opinion, the question of whether genetic change occurs in hatcheries has been answered," Blouin said. "If we could quit arguing about that and find out why, then we're all on the same team again."
The research is the latest in a series of genetic studies of Hood River steelhead, helped by a remarkable collection of tissue samples from every steelhead returning to the river from 1991 to 2010.
The study, "Genetic adaptation to captivity can occur in a single generation," was authored by Christie, Blouin, Melanie Marine of OSU and Rod French of the Oregon Department of Fish and Wildlife.
Hatcheries Change Salmon Genetics After a Single Generation by Staff, Science Daily, 12/20/11
Agencies Scoping Plan For 'Hatchery Effects Evaluation Team' by Staff, Columbia Basin Bulletin, 1/13/12
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