Deadly parasite killing Yukon River king salmon

Posted: Sunday, May 06, 2001

ANCHORAGE (AP) -- A common parasite is killing king salmon in the upper Yukon River.

Nearly a quarter of the fish entering the river last year were infected with ichthyophonus, which first appeared in the drainage in 1987, according to Richard Kocan, a fish pathologist at the University of Washington.

Salmon spawning in lower river tributaries appear able to live with the infection. But those headed upriver, particularly the fish bound for Canadian tributaries of the Yukon, are suffering.

Kocan reported that more than 20 percent of the kings found near the village of Tanana showed signs of the disease. Ichthyophonus not only weakens the fish but renders the flesh almost inedible.

''They stink,'' Kocan told the Anchorage Daily News. ''They smell bad. They don't dry.''

Kocan has theorized that the Yukon kings might have picked up ichthyophonus from eating infected Bering Sea herring.

Subsistence and commercial fishermen first spotted the problem years ago but said it was pretty rare.

Tanana fisherman Bill Fliris said his curiosity about what was wrong with the salmon led him first to the Alaska Department of Fish and Game and then to a U.S. Fish and Wildlife Service laboratory that in 1997 identified ichthyophonus.

''The first thing we noticed was the odor of the fish,'' Fliris said. ''You hang it in the sun, and you start the drying process, . . . and it doesn't smell bad, it just smells kind of fruity.''

Over the years, Fliris said, as the number of bad salmon increased, he began to notice gray specks in the flesh of the salmon and white bumps that looked like grains of salt on their hearts.

Fliris contacted Kocan, an ichthyophonus expert, after reading the lab reports.

It became hard to ignore the problem when the disease started appearing in about one out of every five fish.

By the time the kings get to Circle near the U.S.-Canada border on the Yukon almost a third of the kings show signs of the disease, Kocan said.

Then a strange thing happens.

The percentage of infected fish at Whitehorse, Yukon, drops from more than 30 percent of female spawners to just 10.5 percent.

Kocan suspects the disease is probably killing tens of thousands of salmon before they get close to their spawning beds. Studies beginning this summer will try to determine whether that is the case.

''It's really disconcerting,'' said Gene Sandone, regional commercial fisheries supervisor for the Alaska Department of Fish and Game.

''They let a lot of fish go up the river, and they assume they get to the spawning beds,'' Fliris said. But if a third of those fish aren't making it, management plans need to change.

Canadian king salmon are already in trouble without ichthyophonus. Returns to the upper Yukon are down to one fish per spawner from a 1980s ratio of six fish per spawner, Sandone said. Such returns make it difficult to have any sort of fishery and maintain the run.

Sandone worries now that the parasite could also show up in Alaska's Kuskokwim River drainage, where king runs are also weak. Ocean survival has been ''absolutely horrible,'' he said.

Poor ocean survival could act with the ichthyophonus outbreak to make things worse. Fish already struggling to survive because of poor ocean food supply, for instance, would be vulnerable to parasites.

''Diseases are usual in low numbers'' in salmon, Sandone said. ''In a stressful situation, the ones that have disease are going to manifest it.''

Compounding the situation is what may be a change in the Yukon itself. Water temperatures hit 17 degrees Celsius, about 63 degrees Fahrenheit, in the summers of 1998 and 1999, Kocan said.

Sandone said warm river water has added to the stress on salmon bound upstream. It's normal to see more diseased fish in such conditions, he said.

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