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Parasite spreading concern on Klamath River


Published June 10, 2004


A parasite that is causing infection and death among young salmon in the lower Klamath River is raising concerns for federal and state officials and other water interests.

The high level of infection in fish comes as a surprise because water conditions in the river are relatively good, sources say.

"It has us real worried," said Dave Sabo, manager of the Klamath Reclamation Project.

U.S. Bureau of Reclamation officials are worried that the Klamath Project will be blamed if something happens to salmon fingerlings being sent down the river from the Iron Gate fish hatchery near Yreka.

The parasite Ceratomyxa shasta, called C shasta for short, is common in the main stem of the Klamath River system, from the Pacific Ocean to the Williamson River.

The microscopic parasite spends part of its life floating in the river as a tiny, 3-millimeter-long worm, said Jerri Bartholomew, an assistant professor of microbiology at Oregon State University.

The worms find their way into the digestive tracts of salmonid fish, which include salmon, steelhead and trout.

Some fish are resistant to the parasite. Most are not.

Inside the fish's intestine, the parasite feeds on tissue and reproduces, often killing the fish by causing an infection.

Depending on the water temperature and other factors, the fish will die within 20 to 30 days after the parasite has entered it. The warmer the temperature, the faster the spread of the parasite and possible spread of infection.

"We are seeing a high incidence of disease in our out-migrant fish," said Toz Soto, fisheries biologist for the Karuk Tribe, one of the downstream tribes.

"It's always around, but we are really concerned because the infection rate seems to be really high this year," Soto said.

In early May, scientists on the Klamath River started finding dead salmon fingerlings in traps between I-5 and the Scott River, said Al Donner, spokesman for the U.S. Fish and Wildlife Service. The parasite has killed 50 to 80 percent of the young salmon in some places.

At the Happy Camp trapping site on the river, tribal scientists found 75 to 80 percent of the young salmon headed downstream appear to be suffering from infection.

Officials and scientists couldn't immediately estimate how many total fish the parasite might kill. It's presumed that some dead fish can't be seen in the murky water, and that birds consume many dead fish before they are seen by scientists.

Adding to the mystery of the infection outbreak is the lack of stressful conditions often blamed when fish start dying.

"The temperatures are good and the oxygen levels are good for fish," said John Engbring, director of the Fish and Wildlife Service's California and Nevada Operations office in Sacramento.

He said scientists will continue to collect samples to try to figure out what is causing the parasite to spread.

"At this point, we don't know if this is more natural, or if there are some human causes that are making it more significant," Engbring said.

Sabo said the Bureau is doing what it can to help the situation, but higher flows might not be the answer.

"We want to make sure that the fishery is as healthy as it can be," Sabo said.

Observers hope the infection doesn't affect as many fish as it did in 2000, when an estimated 300,000 young salmon and steelhead died from the same parasite and a fungus that attacks the gills.

The California Department of Fish and Game released more than 5 million fish from the Iron Gate Fish hatchery over the past month.

The fingerlings were released a million at a time, about four or five days apart, with the first release on May 13 and the last on June 3, said Kim Rushton, hatchery manager. The hatchery also held back 900,000 young salmon to be released in the fall.

The C shasta parasite is just one of the many dangers salmon face in their life cycle. Larger fish, birds, seals and fishermen all take a toll on fish populations.

"You raise millions to get a few thousand back," Rushton said.

He said the average return for each run of adult chinook salmon is 10,000 to 15,000. The hatchery needs 8,000 adults to collect eggs.

The last three or four years have had record runs in the tens of thousands, he added.


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