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Study shows hatchery and wild chinook closely related

Salmon netFocus on man’s reintroduction of fish

Hatchery populations of spring chinook salmon in the subbasins of the upper Willamette River are genetically similar to the wild populations in these basins and should continue to be used for recovery of spring chinook salmon.

That’s the conclusion of a study published in July by Oregon Department of Fish and Wildlife researchers. The research had been identified as high priority by the 2008 Willamette Project biological opinion. Spring chinook salmon of the upper Willamette River basin were first listed in 1999 as threatened under the U.S. Endangered Species Act, a label that had been reaffirmed in 2005 and again in 2010.

Prior to this study the genetic relationships between hatchery and wild chinook salmon in the basin were unknown. Researchers now say the study’s results lend confidence to the current approach for recovery of spring chinook salmon in the upper Willamette River.

“Within sub-basins of the upper Willamette River, hatchery spring chinook appear to be closely related to the local wild populations, with similar or higher levels of genetic diversity,” said Marc Johnson, technical analyst for the Oregon Department of Fish and Wildlife, ODFW Corvallis Research. “Populations among most Willamette subbasins are slightly, but significantly, different from one another.”

The authors are Johnson and Tom Friesen, program manager for ODFW Upper Willamette Salmonid Research, Monitoring and Evaluation, ODFW Corvallis Research Lab.

Their study further concludes that spring chinook salmon that originate in Upper Willamette River hatcheries “represent appropriate founder populations for ongoing reintroduction programs and recommend that the conservation and recovery of this stock proceed through management actions developed specifically for each sub-basin.”

At the same time, the authors recommend that restrictions on hatchery stock transfers within the subbasins of the upper Willamette River continue in order to preserve the genetic structure of the current populations, which is currently a part of the recovery plan for the salmon. According to Johnson, the “Conservation and Recovery Plan authored by ODFW and NOAA recommended treating each subbasin as a unique population, each with its own criteria for recovery.”

Dams in the Upper Willamette River have impeded the move-ment of juvenile and adult salmon in the basin and five state-operated hatcheries are releasing significant numbers of juveniles into the streams of the basin to mitigate for this lost habitat. That could pose a threat to the wild populations if hatchery populations are less diverse.

Although the genetic relationships between hatchery and wild spring chinook salmon stocks had not been shown in previous research, the authors weren’t surprised by this study’s findings since the hatchery brood-stocks were founded by local stocks and hatcheries had historically included some wild fish into the brood. In fact, they found that the hatchery populations are most genetically similar to the local wild populations from the same subbasin.

“We observed that most of the genetic diversity in upper Willamette chinook salmon could be found in every population, represented by multiple alleles within and among individuals of each population,” Johnson said.

Still, factors other than genetic makeup can affect the productivity of salmon populations.

“While the Willamette hatchery programs appear to be effective at maintaining demographically robust and genetically diverse salmon populations, we cannot assume that they produce fish that are well-suited to survive and reproduce in the wild,” Johnson said. “The reproductive success of Willamette hatchery chinook in the wild is the subject of ongoing research by Oregon State University, and information from that work will undoubtedly help managers to chart the best course to recovery for this stock.”

Extensive releases of hatchery juveniles have failed to result in “wild adult returns despite apparently substantial natural production of juveniles,” the report says.

“These results underscore both the potential of hatchery-origin fish for local reintroduction programs and the fundamental role that improved dam passage must play to secure the long-term viability of spring chinook salmon in the upper Willamette River,” the report concludes.

Image above: Ongoing studies in the Pacific Northwest will continue to monitor the interactions between natural fish stocks and those raised as hatchery brood-stocks.


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