Quick Productivity Decline
by Bill Rudolph
"Genetic adaptation to captivity can occur in a single generation,"
Oregon State University researchers say it only takes one generation in the wild for the most productive hatchery steelhead from Oregon's Hood River to exhibit much lower productivity than hatchery steelhead which produce less than five siblings, according to a paper published in Proceedings of the National Academy of Sciences, a few weeks ago. Their article, "Genetic adaptation to captivity can occur in a single generation," reported that amounted to a whopping 71 percent less productivity.
Earlier results from Hood River studies found that hatchery-born fish with two wild parents averaged 85 percent of the reproductive success of wild counterparts.
"We expected to see some of these changes after multiple generations," said Mark Christie, lead author and an OSU post-doc, in an OSU press release. "To see these changes happen in a single generation was amazing. Evolutionary change doesn't always take thousands of years."
It's the latest finding by OSU researchers, who have been studying Hood River steelhead for many years, and it's sure to give more ammunition for foes of supplementation--the practice of using hatchery-bred fish to help boost ESA-listed and other weak fish populations in the Columbia Basin. Whole hatchery programs, like the spring chinook produced at the Cle Elum facility, are being funded as a grand experiment.
But the researchers were cautious about drawing any large conclusions from the study. "It remains to be seen whether results from this one study on steelhead generalize to other hatcheries or salmon species," said Michael Blouin, OSU professor of zoology.
They also noted that in 4 out of 5 run-years, hatchery broodstock had nearly twice the reproductive success of wild broodstock, "which is a pattern consistent with adaptation to captivity."
The authors speculated that a combination of traits may be responsible for the large decline in productivity, including faster growth rates for hatchery steelhead--one year in the hatchery before release, compared to wild fish which usually take two years to smolt. Other traits that may contribute to the decline in productivity include, egg size, fecundity, physiological processes associated with smoltification, along with individual behaviors like predator avoidance. Crowding in hatcheries may be another selection pressure, since in one run-year, smolts were raised in considerably low-density conditions and their release size was much larger.
"Understanding that unintentional selection in captivity can cause rapid fitness declines has important conservation and management implications. Determining which traits are under selection and whether captive breeding programs can be modified to mitigate those selection pressures will be the next big challenge for improving the science of captive breeding," said the authors.
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