[4] New Study Says Hatchery Steelhead Fitness Shows Rapid Decline In Wild
An article published in last week's Science has raised more questions about the value of using hatchery fish to boost wild fish runs. By studying several generations of steelhead that returned to Oregon's Hood River, the researchers from Oregon State University found that the fitness of hatchery steelhead that spawn in the wild is significantly reduced.
Authors Hitoshi Araki, Becky Cooper and Michael Blouin used hatchery and wild steelhead data from Hood River to reconstruct a "three-generation pedigree with microsatellite markers" to estimate that reproductive fitness was reduced by about 40 percent per generation for two generations of steelhead that spawned in the wild after beginning life at the Hood River hatchery facility. However, the results seem to contradict a 2006 paper produced by the trio that found no essential difference in the reproductive success of hatchery-origin and wild steelhead after one generation in natural surroundings.
But the authors say the earlier results "neglected the fact that captive-reared and wild individuals experience different environments as juveniles, which might affect mating behaviors, fecundity, and/or fertility. Therefore it is difficult to disentangle environmental effects from genetic effects of a difference or lack of difference in reproductive success."
So they compared the reproductive success of two types of captive-reared fish, one from two wild parents, and the other from a wild parent and a first-generation captive-reared parent, born in the same year, reared in the same hatchery and released at the same time.
They said the evolutionary mechanism causing the decline in fitness was unknown, but they "suspect that unintentional domestication selection and relaxation of natural selection, due to artificially modified and well-protected rearing environments for hatchery fish, are probably occurring." And they caution that the repeated use of captive-reared fish to supplement declining populations "should be carefully reconsidered."
Their work was funded by BPA, which has put a lot of its salmon eggs into the future of supplementation hatcheries for improving ESA-listed stocks in the Columbia, judging from its latest plan to recover ESA-listed stocks.
Ernie Brannon, retired fisheries professor from the University of Idaho, and an expert on Northwest hatcheries, told NW Fishletter in an email that the OSU researchers' work "appears as a well designed study and it required a lot of time in years to accomplish. It is interesting that all of this negative effect was linked to only half of the genome that was hatchery in origin!!"
Brannon said he was waiting to see more details of the work, which he hoped would continue. However, he cautioned that there were many things to consider before eliminating all hatchery fish. "Based on the preliminary paper, I think the issues that have to be carefully reconsidered before they are justified in making their conclusions are (1) the large variability that they got between return years, (2) the small number of fish in their samples (six categories - three years of C(W x W) and C(C xW) which can have a major influence on the analysis, (3) the assumption that their DNA markers are neutral, (4) what physical marks were employed in the C and W categories, if any, (5) the problem with the C(W x W) performance between the 1st and 2nd studies, (6) the declaration that the reduction in return success was a genetic effect, (7) the thought that their study immediately applies to all hatchery fish as a general application of their conclusions, rather than just to the Hood River hatchery study returns for the 1996 brood year releases, (8) the use of smolt to adult data rather than egg to adult data to make their analysis, (9) ignoring the reproductive potential of the naturally spawned progeny in subsequent generations of naturally spawning fish, and (10) jumping to the conclusion that use of captive reared organisms (hatchery fish) for reproduction of captive-reared progeny (supplementation) should be carefully reconsidered.
"These are red flags that suggest a biased beginning, as well as their interpretation of the references they used," said Brannon. "Even if the reduction of 40 percent in reproduction performance per captive generation was real, the fact that 95 percent of your wild fish die before migrating to sea compared to < 30 percent of hatchery fish still makes supplementation a recovery tool to put natural spawners on the spawning beds.
"It is not new that hatchery fish spawning in the wild can show lower performance than wild fish," he added, "and Araki's study really isn't showing anything different. How will the now wild progeny do in subsequent generations is the real question." -B. R.
The following links were mentioned in this story:
NW Fishletter #209, January 31, 2006
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