Wednesday, June 10,
2009
Steelhead trout that are originally bred in hatcheries are so
genetically impaired that, even if they survive and reproduce in
the wild, their offspring will also be significantly less
successful at reproducing, according to a new study published today
by researchers from Oregon State University.
The poor reproductive fitness – the ability to survive and
reproduce – of the wild-born offspring of hatchery fish means that
adding hatchery fish to wild populations may ultimately be hurting
efforts to sustain those wild runs, scientists said.
The study found that a fish born in the wild as the offspring of
two hatchery-reared steelhead averaged only 37 percent the
reproductive fitness of a fish with two wild parents, and 87
percent the fitness if one parent was wild and one was from a
hatchery. Most importantly, these differences were still detectable
after a full generation of natural selection in the wild.
The effect of hatcheries on reproductive fitness in succeeding
generations had been predicted in theory, experts say, but until
now had never been demonstrated in actual field experiments.
"If anyone ever had any doubts about the genetic differences
between hatchery and wild fish, the data are now pretty clear,"
said Michael Blouin, an OSU professor of zoology. "The effect is so
strong that it carries over into the first wild-born generation.
Even if fish are born in the wild and survive to reproduce, those
adults that had hatchery parents still produce substantially fewer
surviving offspring than those with wild parents. That's pretty
remarkable."
An earlier report, published in 2007 in the journal Science, had
already shown that hatchery fish that migrate to the ocean and
return to spawn leave far fewer offspring than their wild
relatives. The newest findings suggest the problem does not end
there, but carries over into their wild-born descendants.
The implication, Blouin said, is that hatchery salmonids – many of
which do survive to reproduce in the wild– could be gradually
reducing the fitness of the wild populations with which they
interbreed. Those hatchery fish provide one more hurdle to overcome
in the goal of sustaining wild runs, along with problems caused by
dams, loss or degradation of habitat, pollution, overfishing and
other causes.
Aside from weakening the wild gene pool, the release of
captive-bred fish also raises the risk of introducing diseases and
increasing competition for limited resources, the report
noted.
This research, which was just published in Biology Letters, was
supported by grants from the Bonneville Power Administration and
the Oregon Department of Fish and Wildlife. It was based on years
of genetic analysis of thousands of steelhead trout in Oregon's
Hood River, in field work dating back to 1991. Scientists have been
able to genetically "fingerprint" three generations of returning
fish to determine who their parents were, and whether or not they
were wild or hatchery fish.
The underlying problem, experts say, is Darwinian natural
selection.
Fish that do well in the safe, quiet world of the hatcheries are
selected to be different than those that do well in a much more
hostile and predatory real-world environment. Using wild fish as
brood stock each year should lessen the problem, but it was just
that type of hatchery fish that were used in the Hood River study.
This demonstrates that even a single generation of hatchery culture
can still have strong effects.
Although this study was done with steelhead trout, it would be
reasonable to extrapolate its results to other salmonids,
researchers said. It's less clear what the findings mean to the
many other species that are now being bred in captivity in efforts
to help wild populations recover, Blouin said, but it's possible
that similar effects could be found.
Captive breeding is now a cornerstone of recovery efforts by
conservation programs for many threatened or endangered species,
the researchers noted in their report. Thousands of species may
require captive breeding to prevent their extinction in the next
200 years – which makes it particularly important to find out if
such programs will ultimately work. This study raises doubts.
"The message should be clear," the researchers wrote in their
report's conclusion. "Captive breeding for reintroduction or
supplementation can have a serious, long-term downside in some
taxa, and so should not be considered as a panacea for the recovery
of all endangered populations."
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Oregon State University
Thanks to Oregon State University
for this article.