Some spring Chinook salmon adults returning to the Willamette and Deschutes river basins have been found to be infected by Ceratomyxa shasta (c. shasta), a parasite-driven disease that is contracted by the fish while in the river and that can kill adults before they spawn.
While it’s not unusual for the parasite to reside in rivers of the Columbia River basin-- such as the Lewis, Cowlitz, Willamette and Deschutes rivers and up through the Snake River basin --this year with warmer water and lower flows, the damage to spring Chinook is more severe.
Since 2002, c. shasta has devastated salmon in the Klamath River in southern Oregon and Northern California, where this year, due to extremely low flows and warm water, the parasite has invaded more than three quarters of juvenile out-migrants.
While the severity does not match that of the Klamath River, researchers are still finding infected adult fish in at least two Columbia River basin streams, according to Craig Banner, senior fish health specialist, Fish Health Services, Department of Microbiology, Oregon Department of Fish and Wildlife.
Banner said that fewer spring Chinook salmon than expected have returned this year to Warm Springs and Round Butte fish hatcheries on the Deschutes River in Central Oregon and that some that did return had signs that c. shasta was taking its toll. He was hesitant to point to the parasite as the cause of the overall poor return of fish on the Deschutes River. Many of the fish, he said, had rough gills as a result of another pathogen. “The bottom line is that not as many fish came back this year,” he said.
However, Willamette River spring Chinook salmon are showing signs of harsher physical damage.
“c. shasta is always present and we always find it in a portion of the adult fish,” Banner said. “However, this year, in a portion of our adult fish, the parasite seems to be causing more dramatic pathogenic damage.”
The parasite usually settles in the intestines of fish, both juvenile and adult fish that have been exposed. This year, he said, biologists studying adult spring chinook salmon in the Willamette River are also seeing more of the parasite in livers, spleens and kidneys of the fish, even though chinook salmon are “somewhat resistant” to the effects of the parasite.
“Resistance, however, is related to how much the fish is exposed to the parasite,” he said. “Unusually high exposure leaves them less resistant to the disease.”
He is not sure why there would be a higher exposure of the parasite to salmon this year, but pointed to stream conditions, warmer water and lower flows, as having the potential to increase the presence of c. shasta.
“These are bad conditions for fish, but good conditions for the parasite,” he said.
For adult salmon, there is little visual indication to the lay person that c. shasta parasites reside within the fish, nor is there any particular damage to the flesh of the fish, and eating the fish is not harmful to humans, Banner said.
Once the salmon picks up c. shasta from the water, incubation to full-fledged parasite takes 14 to 40 days before a salmon could die. The fish could have picked up the parasite anywhere along their journey to spawning after they arrive in the fresh water of the Columbia River. Or, they may have been exposed in the Willamette River or the Deschutes River, where warmer water and lower flows are more conducive to the parasite’s presence.
ODFW has not completed field studies to determine the full impact this year of the parasite on adult or juvenile salmon populations in the Willamette River. However, it is collecting pathology samples from the intestines, liver, spleen and kidneys of fish in the river.
In addition, one of the leading authorities on c. Shasta is collecting water samples in the Willamette River, looking at the presence of c. shasta in the water. Professor Jerri Bartholomew, director of the John L. Fryer Salmon Disease Laboratory at Oregon State University, did graduate work on the parasite in the late 1980s. For more than a decade she has been especially busy leading research of c. shasta in the Klamath River Basin, where the parasite is far more prevalent and damaging to fish runs.
Bartholomew confirmed that temperature and flow has a lot to do with the severity of the infection, pointing to conditions in the Klamath River, where extreme low flows and high water temperatures caused by an exceptionally poor snow pack this winter, are devastating salmon.
Nick Hetrick, supervisory fish biologist (Fisheries Program Lead), at the U.S. Fish & Wildlife Service’s Arcata, Calif. office, said the snow pack in the upper Klamath River was as low as 15 percent of normal this year, but the Trinity River’s snowpack, which flows into the Klamath River further downstream, was near zero.
A survey this summer of juvenile fall chinook out-migrants in the Klamath River found that c. shasta was present in 76.5 percent of chinook salmon juveniles and that another parasite, Parvicapsula minibicornis, was detected in 86 percent of juveniles (http://www.fws.gov/Arcata/fisheries/projectUpdates/FishHealthMonitoring/Klamath%20Juvenile%20Salmonid%20Health%20Update%20July%2028%202014.pdf). Last year, c. shasta was present in just 5 percent of fish. The impact of the parasite on juveniles is more visually apparent than in adult fish, as they develop soft flesh and distended stomachs since the parasite inhabits the intestines of fish.
Neither Hetrick nor Bartholomew would predict the impact of the infection in juvenile fish on actual adult returns, but both said it could be significant.
Bartholomew also has conducted water surveys in the Klamath River, similar to the surveys she is conducting in the Willamette River. In 2013, her crew of researchers found c. shasta in the water six out of the 12 weeks of the survey. This year they found the parasite in each of the 12 weeks. On the Klamath River, when parasite abundance is greater than 10 parasites for every liter of river water, it triggers a pulse of water from upstream dams to cool the river and reduce what are ideal conditions for the parasite. That occurred this year in May, but it was a small pulse of water and the basin has very little water to continue these pulses, she said.
c. shasta has long been a presence in the Columbia River watershed (see “Geographic distribution of Ceratomyxa shasta in the Columbia River basin and susceptibility of salmonid stocks” by Bartholomew at https://ir.library.oregonstate.edu/xmlui/handle/1957/21962
However, this is the first time that researchers have collected water samples in the Willamette River and there isn’t any river in the Columbia River basin in which c. shasta abundance would automatically trigger a pulse of water to cool the river as in the Klamath River.
Columbia Basin Bulletin
The Columbia Basin Bulletin e-mail newsletter is produced by Intermountain Communications of Bend, Oregon and supported with Bonneville Power Administration fish and wildlife funds through the Northwest Power and Conservation Council's Columbia Basin Fish and Wildlife Program.
Articles republished by The Dalles Chronicle with permission.