A new study, published in Biology Letters and supported by grants from the Bonneville Power Administration and the Oregon Department of Fish and Wildlife, explains that steelhead trout that are bred in hatcheries are significantly genetically impaired, causing poor reproductive fitness. They are so impaired that, even if they survive to reproduce in the wild, the chances that they will produce viable, fertile offspring are startlingly low. This means that adding hatchery fish to the wild populations of fish is more likely to cause problems than to help solve them.
Steelhead Trout
Previous predictions that hatcheries have a negative effect reproductive fitness have been noted but this is the first study to prove it with field experiments. After years of genetic analysis of thousands of steelhead trout, the study concluded that fish born in the wild to two hatchery-raised steelhead have only 37 percent the reproductive fitness of a fish born to two wild steelhead. A fish born to one wild and one hatchery-raised fish has only 87 percent the reproductive fitness. Even after a full generation in the wild these differences were still measurable.
“If anyone ever had any doubts about the genetic differences between hatchery and wild fish, the data are now pretty clear,” says Michael Blouin, a professor of zoology at Oregon State University.
A previous report, published in the journal Science in 2007, had shown that hatchery fish that migrate to the ocean and return to spawn leave far fewer offspring than the wild ones. This new study shows that the effects do not stop there. “The effect is so strong that it carries over into the first wild-born generation,” says Blouin. “Even if fish are born in the wild and survive to reproduce, those adults that had hatchery parents still produce substantially fewer surviving offspring that those with wild parents.”
The main problem is that hatchery salmonids are potentially reducing the fitness of the wild populations with which they interact and reproduce, when the original goal was to boost those populations. This is just one more problem to be added to the list of things that interfere with sustaining the wild runs of fish like steelhead trout and salmon, like habitat loss and degradation, pollution and overfishing.
Copyright © 2009 by Marine Science Today, a publication of OceanLines LLC
