New Hood River Study: Spawning Hatchery Steelhead Have Little Influence on Wild Fish Productivity

July 28, 2022
New Hood River Study: Spawning Hatchery Steelhead Have Little Influence on Wild Fish Productivity

Though federal and state biologists have agreed to stop releasing hatchery winter and summer steelhead into the Hood River basin, a new study says that hatchery fish spawning in the river have little influence on wild winter steelhead productivity. Other variables, such as stream flow, abundance of sea lions in the Columbia River and ocean conditions have more influence than hatchery fish on the river’s spawning grounds. By 2025, except for a few hatchery strays, steelhead returns to the Hood River and its tributaries will be wild steelhead only and there are two major reasons for the change. Up to 2010 when PacifiCorp’s Powerdale Dam was removed, returning hatchery fish were sorted and prevented from traveling upstream to spawning grounds. Without the dam, capturing the fish with a weir proved to be too difficult.

But the second major reason is that the Bonneville Power Administration had expressed concerns about long-term studies it had funded indicating that allowing too many hatchery fish on the spawning grounds reduces the genetic fitness of the wild fish, which are listed as threatened under the Endangered Species Act. The new study seems to say the closure of the Hood River to hatchery fish due to influences on wild steelhead genetic fitness is misguided.“The broad assertion that hatchery fish negatively impact wild fish is a crude oversimplification,” said Ian Courter of Mount, Hood Environmental, Boring, OR, one of the new study’s authors. “The hatchery fish science debate has been overwhelmed by mechanistic theories about hatchery fish impacts on wild fish.

Those studies are useful for crafting hypotheses, but those hypotheses should not be used to infer population-scale impacts. Theoretical effects mechanisms need to be tested against population-scale metrics like abundance and productivity if our intent is to make population-scale inferences.” “Given our findings, the theory that hatchery-origin steelhead were a significant threat to Hood River winter steelhead viability appears to be inadequately supported,” Courter continued. The team of scientists “estimated the effect of the proportion of hatchery-origin spawners (pHOS), proportionate natural influence (PNI), and hatchery fish releases on natural adult winter steelhead recruitment in the Hood River in north Oregon over a 27-year period of record,” the study says.

It found that “Adult winter steelhead productivity was not associated with pHOS and PNI.”(PNI: Estimate of the relative selection pressure of the natural environment in an integrated natural / hatchery population.)The study said that pHOS and PNI are the primary metrics for inferring genetic risks of hatchery programs in the Pacific Northwest.“ Some researchers theorize that hatchery-origin steelhead can reduce the fitness of natural-origin populations through the transfer of maladaptive genes,” Courter said. “However, we did not find evidence that productivity of the Hood River steelhead population was affected by the presence of hatchery-origin spawners.”Summer steelhead hatchery releases started in 1956, but ended when the Powerdale Dam was removed.

Winter steelhead hatchery releases began in 1962. The last release of winter steelhead smolts into the river was in 2021.About 100-500 wild summer steelhead return to the river and about 250-1,200 wild winter steelhead return.A 2009 study led by Oregon State University zoology professor Michael Blouin found 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 study concluded. The effect of hatcheries on reproductive fitness in succeeding generations had been predicted in theory, experts said at the time, but until the Blouin study 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 Blouin said in 2009. “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.” Courter agrees that the Blouin et al. genetics studies demonstrated that hatchery and natural-origin steelhead in the Hood River have different relative reproductive success rates in the wild. However, the Blouin study did not demonstrate that hatchery fish negatively impacted the wild fish, he said. “In other words, Blouin et al. provided evidence for a possible mechanism of impact, and our study demonstrated that those impacts, if they occur, appear to be small relative to other variables that influence winter steelhead production in the Hood River,” Courter said.At the time of Blouin’s study (2009), the Columbia River Inter-Tribal Fish Commission and its four member tribes (Umatilla, Warm Springs, Yakama, and Nez Perce) had concerns over his study and some tribal biologists are a part of this current open access study, titled “Hatchery propagation did not reduce natural steelhead productivity relative to habitat conditions and predation in a mid-Columbia River subbasin,” published June 21, 2022 in the Canadian Journal of Fisheries and Aquatic Sciences.

Courter’s co-authors are Tom Chance with the Lummi Nation in Bellingham, WA; Ryan Gerstenberger, Confederated Tribes of the Warm Springs; Mark Roes and Sean Gibbs, Mount Hood Environmental; and Adrian P. Spidle, Northwest Indian Fisheries Association, Olympia, WA. The Courter et al study cited recent findings from a long-term study of Chinook salmon in Johnson Creek in Idaho, saying that that study demonstrated that hatchery fish spawning with natural-origin fish had similar reproductive success relative to natural-origin pairs and that hatchery supplementation provided a demographic boost to the population (Janowitz‐Koch et al. 2019).

“While studies of relative reproductive success provide insight about the influence of captive rearing on individual fitness, the effect of fitness loss on population productivity in the naturally spawning population is not directly quantified,” the Courter et al study says. “Surprisingly,” the study says, “the number of juvenile hatchery steelhead released annually into the Hood River was positively related to natural-origin steelhead recruitment.” One explanation for this finding could be “predator swamping” where hatchery releases of juvenile winter steelhead may have been insulating natural origin fish from avian predators. “It is also possible that hatchery supplementation increased density of natural-origin spawners (Scheuerlerell et al, 2015) and diversified the population’s demography as was observed by Janowitz-Koch et al (2019),” the study says.

On average, California and Stellar sea lions consume 6.8 percent of adult steelhead and 2.7 percent of spring Chinook salmon arriving at Bonneville Dam. Bite marks were seen on about 22 percent of salmon and steelhead returns to the Hood River basin (Simpson et al. 2016). “Consequently, we observed a negative association between abundance of California and Stellar sea lions and Hood River steelhead productivity,” the study says. And, they found that ocean conditions impacted Hood River steelhead production and that low or minimum stream flows impacted juvenile steelhead rearing in the river during their first year. “Our analysis highlights the importance of directly testing theories about the influence of hatchery fish on steelhead populations using abundance monitoring data.

Hatchery steelhead effects should also be examined in the context of other factors that influence natural-origin fish recruitment to avoid overstating the expected conservation benefits of reducing or eliminating hatchery programs,” the Courter et al study concludes. “In the case of Hood River winter-run steelhead, interactions between hatchery and natural-origin fish did not have a quantifiable negative impact on population productivity, suggesting that an integrated broodstock program implemented to augment harvest opportunity should not be expected to impair ecosystem-based efforts to enhance natural-origin fish abundance.” -Mike O'Bryant

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