Steelhead Losing Reproductive Ability in Hatcheries

Steelhead Losing Reproductive Ability in Hatcheries



October 2007

 The rearing of steelhead trout 
in hatcheries causes a rapid drop in their ability to reproduce in the 
wild, a new Oregon State University study shows. Researchers say their 
findings raise serious questions about the wisdom of historic hatchery 
practices. 
The research, published Friday in the journal "Science," demonstrates for 
the first time that the reproductive success of steelhead trout, an 
important salmonid species, can drop by close to 40 percent per 
captive-reared generation. The study reflects data from experiments in 
Oregon's Hood River. 
"For fish to so quickly lose their ability to reproduce is stunning, it's 
just remarkable," said Michael Blouin, an OSU associate professor of 
zoology. "We were not surprised at the type of effect but at the speed. We 
thought it would be more gradual. If it weren't our own data I would have 
difficulty believing the results." 
The research was conducted through use of 15 years of DNA tracking 
technology of fish breeding in Hood River, a mountain stream that flows 
northward off Mount Hood into the Columbia River. DNA analysis with scales 
was done with about 15,000 fish since 1991. 
The was financially supported by the Bonneville Power Administration and 
the Oregon Department of Fish and Wildlife. 
Researchers found that fish reared in a hatchery for two generations had 
around half the reproductive fitness of fish reared for a single 
generation. 
The effects appear to be genetic, scientists said, and probably result 
from evolutionary pressures that quickly select for characteristics that 
are favored in the safe, placid world of the hatchery, but not in the 
comparatively hostile natural environment. 
"Among other things, this study proves with no doubt that wild fish and 
hatchery fish are not the same, despite their appearances," said Blouin. 
"Some have suggested that hatchery and wild fish are equivalent, but these 
data really put the final nail in the coffin of that argument." 
Even a few generations of domestication may have significant negative 
effects, and repeated use of captive-reared parents to supplement wild 
populations "should be carefully reconsidered," the scientists said in 
their report. 
Traditionally, salmon and steelhead hatcheries obtained their brood stock 
and eggs from fish that were repeatedly bred in hatcheries - they tended 
to be more docile, adapted well to surface feeding, and they thrived and 
survived at an 85-95 percent level in the safe hatchery environment. 
More recently, some "supplementation" hatchery operations have moved to 
the use of wild fish for their brood stock, on the theory that their 
offspring would retain more ability to survive and reproduce in the wild, 
and perhaps help rebuild threatened populations. 
"What happens to wild populations when they interbreed with hatchery fish 
still remains an open question," Blouin said. "But there is good reason to 
be worried." 
Earlier work by researchers from OSU and the Oregon Department of Fish and 
Wildlife had suggested that first-generation hatchery fish from wild brood 
stock probably were not a concern, and indeed could provide a short-term 
boost to a wild population. But the newest findings call even that 
conclusion into question, Blouin said. 
"The problem is in the second and subsequent generations," Blouin said. 
"There is now no question that using fish of hatchery ancestry to produce 
more hatchery fish quickly results in stocks that perform poorly in 
nature." 
Evolution can rapidly select for fish of certain types, experts say, 
because of the huge numbers of eggs and smolts produced and the relatively 
few fish that survive to adulthood. About 10,000 eggs can eventually turn 
into fewer than 100 adults, Blouin said, and these are genetically 
selected for whatever characteristics favored their survival. 
Offspring that inherit traits favored in hatchery fish can be at a serious 
disadvantage in the wild where they face risks such as an uncertain food 
supply and many predators. 
Because of the intense pressures of natural selection, Blouin said, salmon 
and steelhead populations would probably quickly revert to their natural 
state once hatchery fish were removed. 
But just removing hatchery fish may not ensure the survival of wild 
populations. Studies such as this consider only the genetic background of 
fish and the effects of hatchery selection on those genetics, and not 
other issues that may also affect salmon or steelhead fisheries, such as 
pollution, stream degradation or climate change. 
Blouin cautioned that these data should not be used to condemn all 
hatchery programs. 
"Hatcheries can have a place in fisheries management," he said. "The key 
issue is how to minimize their impacts on wild populations." 

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