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Scientists link salmon die-off to tissue-eating bacteria, parasite
Thousands of adult salmon dying in the lower Klamath River probably are being killed by bacteria that eat gill tissue and by a parasite that destroys the digestive tract, federal scientists said Friday.
By Jonathan Brinckman
The Oregonian
September 28, 2002
Thousands of adult salmon dying in the lower Klamath River probably are
being killed by bacteria that eat gill tissue and by a parasite that destroys the digestive tract, federal scientists said Friday.
Although they're still uncertain exactly what triggered the outbreaks of
disease, scientists think they were linked to low river flows. Lower than
normal flows in the Klamath River appear to have brought the fish closer
together during their migration to spawning grounds upstream, concentrating the disease-causing organisms.
The low flows also raised water temperatures higher than normal, scientists said. Salmon are more susceptible to disease in water that is warmer than 68 degrees Fahrenheit. Temperatures in the river this week have been as high as 72 degrees.
By Thursday, officials had counted at least 12,000 dead fish in a 40-mile
stretch of the lower Klamath, but estimates of the toll ranged as high as
30,000.
David Hillemeier, fisheries program manage for the Yurok Tribe, said the
dead fish probably will be left to decompose naturally in the Klamath River.
But Patricia Foulk, a spokeswoman for the U.S. Fish and Wildlife Service,
said the agency was considering removing the dead salmon from the river,
and either barging the fish to sea or burying them.
"This is a catastrophe which in my mind is unprecedented," said Dan Free, a
biologist with the National Marine Fisheries Service. "It is safe to say
that fish can't experience this level of mortality and survive in the long
run."
About 30 percent of the water in the lower Klamath River flows from Upper
Klamath Lake. The U.S. Bureau of Reclamation, which operates a dam at the
lake for irrigation, said Friday it would increase the outflow from the
lake at midnight to 1,300 cubic feet per second from 760 cubic feet per
second. The fisheries service requested the increase.
The U.S. Fish and Wildlife Service collected dead fish from the river this
week and last week and sent them to a pathology laboratory in Anderson,
Calif. Final results from the necropsies will not be available until next
week.
Foulk said scientists had tentatively identified columnaris, a bacteria
that eat gill tissue, and Ceratomyxa shasta, a parasite that destroys the
surface layer of the digestive tract. "It looks like these fish were hit
with a double whammy," she said.
Both diseases are present normally in the Klamath River. Usually, however,
the few fish that succumb to the diseases each year are eaten by birds and
other scavengers. The difference this year appears to be the low river
levels and warmer water, scientists said.
On Friday, the flow rate at the mouth of the Klamath River was 38.6 percent
below normal for the date, at 2,170 cubic feet per second compared with the normal 3,533 cubic feet per second. The water temperature on Friday was 68 degrees, the upper end of the range that scientists say salmon need for survival.
"Everything seems to have come together at the wrong time for these fish,"
said Tony Amandi, a fish pathologist with the Oregon Department of Fish and Wildlife. "There was low flow, warm water, and the disease-causing
organisms were present."
Columnaris is one of several kinds of gill disease that kills fish. Some
are caused by fungi, some by parasites. Fish infected by columnaris lose
parts of their gills and have gills stained yellow by bacteria colonies.
Fish with columnaris die of suffocation.
Ceratomyxa shasta is a parasite that spends part of its life infesting
marine worms and part of its life in fish. Infected fish die because they
can no longer control their digestion or because of bacterial infections in
the parts of their intestines that have been perforated.
Warm water exacerbates both diseases, and low river flows can spread the
disease by increasing the concentration of disease-causing organisms,
Amandi said.
Large numbers of fish carcasses in the river could harm other fish, he
said. For one thing, decaying fish bodies can lower oxygen content of the
water because bacteria and other organisms that consume dead fish use up oxygen.
Also, he said, the disease-causing parasites that leave fish bodies as they
decompose can infect other fish. Neither columnaris nor Ceratomyxa shasta
harms birds or mammals, Amandi said
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