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Though A Concern, Researchers Say ‘Whirling Disease' Unlikely To Take Hold In Upper Deschutes
Posted on Friday, September 24, 2010 (PST)

One of the considerations in planning for the reintroduction of salmon and steelhead above the three-dam Pelton Round Butte Hydroelectric Project on the Deschutes River in central Oregon was to determine the risk of introducing fish disease above dams.

 

Of particular concern has been the westward spreading "whirling disease," which has demonstrated the ability to cause high mortality rates in juvenile salmonids. The disease is known to be carried into the lower Deschutes River by adult salmon that stray on their return to regions of the upper Columbia-Snake river basin where whirling disease is well established.

 

A newly published paper says that researchers have confirmed that M. cerebralis -- a microscopic parasite that causes the disease -- has been identified in fish in the Deschutes River basin below the dams, which are located about 100 miles upriver from the river's confluence with the Columbia.

 

"Continued introduction of the parasite into the river system below the PRB via stray hatchery summer steelhead was also documented. These findings have implications for managing movement of M. cerebralis within the watershed," according to "Detection of Myxobolus cerebralis in the Lower Deschutes River Basin, Oregon," Christopher M. Zielinski, Harriet. V. Lorz, and Jerri L. Bartholomew of Oregon State University. The research paper was published in the August 2010 edition of the American Fisheries Society's "North American Journal of Fisheries Management."

 

But given the fact that the upper Deschutes would seem to be a relatively inhospitable environment for M. cerebralis, researchers believe that the disease is not likely to become broadly established, according to a separate paper developed by Zielinski for the Pelton Round Butte Fish Committee. "Risk of the Introduction and Establishment of Salmonid Whirling Disease in the Deschutes River Basin, Oregon, USA" was completed in October 2009.

 

The paper was lead author Zielinski's master's thesis. Bartholomew and Lorz were Zielinski's advisers on the master's project. The paper can be found at: http://ir.library.oregonstate.edu/jspui/handle/1957/10149

 

"The highest risk for introducing M. cerebralis into the upper Deschutes River Basin is by indiscriminate movement of adult salmonids for reintroduction purposes. Lower risks are associated with moving Deschutes River hatchery fish, eyed eggs, and fry raised in pathogen free water and the movement of marked returning adults," the report says.

 

The later course is the path chosen by Portland General Electric, the Warm Springs tribes and the Oregon Department of Fish and Wildlife, all of which are involved in the reintroduction effort.

 

Part of the process for evaluating the passage plan was the development of a fish health management program. The program is designed, in part, to minimize and communicate the magnitude of risk associated with passing serious fish pathogens upstream of the dams until evaluation of the fish passage effort confirms that the re-establishment of anadromous fish species can be successful.

 

The dam complex has long served as a barrier to upstream migrating native fish populations of summer steelhead trout and spring chinook and sockeye salmon. The dam complex also has isolated bull trout populations upstream from those in tributaries to the Deschutes River downstream of the complex.

 

Both upstream and downstream fish-passage facilities were included in the dam construction but completion of Round Butte Dam in 1964 resulted in confusing surface currents in Lake Billy Chinook, the reservoir upstream. The original fish-passage system was discontinued due to the inability to effectively capture downstream-migrants. The last anadromous fish migrated through the complex in 1968.

 

The scheme for building a juvenile collection facility as part of a one-of-a-kind "selective water control tower" was developed as part of the recent federal relicensing of the hydro project. The tower, in operation for the first time this year, seems to have effectively solved the water current issue. More than 120,000 young fish were collected during the spring-summer season and transported aboard trucks for release in the Deschutes River just downstream of the dams.

 

A majority of the transported fish were kokanee-turned-sockeye, but 42,000 were young spring chinook and 7,800 were steelhead that had been planted as fry upstream in the Deschutes and its tributaries the previous two years. The reintroduction project achieved an important milestone with the initial year's collection effort by attracting more than 50 percent of the Crooked River chinook outmigrants.

 

In order to advance to the project's next step, the reintroduction effort must prove that downstream passage problems have been solved by showing that at least 50 percent of the juvenile fish are finding their way to the collection facility. That next step is the capture of returning adults so that they can be transported upstream and released above the dam to continue on their spawning journey.

 

Each of the young fish captured at the collection facility are marked with a clip of their right maxillary bone, an external bone that extends backwards on the top side of the fishes' mouths. That will allow biologists to identify the fish upon their return.

 

"Initially we're not going to pass any fish that we didn't mark," said Don Ratliff, senior PGE biologist.

 

The fish disease research conducted as part of the effort indicates that whirling disease could become established in the upper Deschutes River, which has as tributaries the Crooked and Metolius rivers. But it is unlikely to thrive.

 

"It will become established, but it will probably not become an issue," said the ODFW's Rick Stocking.

 

The parasite requires two hosts -- salmonid and the aquatic oligochaete worm Tubifex tubifex. The myxospore stage develops within the salmonid host and the triactinomyxon stage -- which when ingested causes the disease in fish -- develops within T. tubifex.

 

"Populations of T. tubifex were found in waters above and below the PRB and had an intermittent or 'patchy' distribution. Of the 63 oligochaete collection locations, only 20 had the confirmed presence of T. tubifex," according toZielinski's risk assessment. And concentrations of the worms were low in the sites where the worms were located.

 

Addtionally, most of the worms found in the Deschutes were of a lineage that is resistant to M. cerebralis and thus cannot transform the parasite into the triactinomyxon stage to which the fish are susceptible.

 

And, "The majority of young salmonids in the Deschutes River Basin emerge and rear during their most susceptible life stages when water temperatures are not conducive for parasite proliferation in either host with the exception of redband trout," according to an executive summary prepared for Zielinski's risk assessment.

 

Stocking said that parasite lives by chewing away at the cartilage of young fish. But in Deschutes fish that cartilage is turned to bone before the temperatures become conducive to parasites.

 

He made the point that the whirling disease parasite has been identified in the Deschutes and in northeast Oregon's Imnaha River. But in neither site has the actual disease gotten a foothold.

 

"We have not seen the disease in Oregon," Stocking said.

 

Elsewhere, in Rocky Mountain states such as Idaho and Montana trout and whitefish populations in a number of streams "have been decimated by this parasite," Stocking said.

 

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