Arctic Science Journeys
Radio Script

salmon racks
King salmon, like these drying on a fish rack along the Yukon River in Interior Alaska, are an important food source for many rural Alaskans. Scientists have found that some king salmon returning home to spawn show signs of a debilitating disease caused by the parasite Ichthyophonus. Photo courtesy Dr. Richard Kocan, University of Washington.
Sick Salmon

INTRO: For years, scientists and fishermen have puzzled over the mysterious declines of salmon along the Yukon River—the vast waterway that stretches 1,500 miles from the Bering Sea through Alaska to headwaters in Canada. Now, thanks to a perceptive fisherman, scientists are one step closer to understanding the river’s salmon crash. Doug Schneider has more in this week’s Arctic Science Journeys Radio.

STORY: Bill Fliris has lived in the remote village of Tanana, on the banks of Alaska's Yukon River, for the past 25 years. Each summer, he catches king salmon weighing 30 pounds or more. The fish feed himself and his family. But over the years, he's watched firsthand as fewer and fewer salmon returned from the sea to spawn. Scientists can't explain the declines, and clues are hard to come by. Now, it turns out that a salmon Fliris caught one day in 1986 may hold at least some of the answers.

FLIRIS: "My wife and I both noticed it. We had this particular fish that was different than the rest. This fish had a funny smell to it. Next year, though, we found a few more of those fish. The year following that, we were actually catching quite a few, and they all had the peculiar smell. It wasn't a rotten smell, but a vegetable smell."

At first, Fliris didn't make too much out of the odd-smelling fish. But within a few years, a quarter of the king salmon he caught each summer smelled funny. The fish had other problems as well.

infected salmon fillet
  Infected king salmon flesh. Photo courtesy Dr. Richad Kocan, University of Washington.
FLIRIS: "What we found were small white or grayish specks in the flesh. Sometimes there'd only be two or three in the whole filleted-out side of a king salmon. Sometimes you'd see it on the heart muscle. It looked like salt sprinkled on the heart muscle. Sometimes there's evidence of it in the liver and spleen."

infected salmon heart
White spots indicate infected king salmon heart. Photo courtesy Dr. Richad Kocan, University of Washington.
In 1998, Fliris sent samples of the fish to federal laboratories, which identified a parasite called Ichthyophonus (pronounced Ick-theo-fonus). With funding from the Bering Sea Fisherman's Association, Dr. Richard Kocan, a fish pathologist at the University of Washington, examined more samples and confirmed the finding.

KOCAN: "Indeed, these fish had Ichthyophonus."

Kocan says Ichthyophonus is common in fish all over the world. But it had only rarely shown up in Yukon River salmon. The parasite can be deadly to salmon, but isn't harmful to people. Last summer, using funds from the U.S./Canada Salmon Treaty, Kocan traveled to Alaska and examined king salmon caught from the river's mouth at the Bering Sea to its headwaters 1,500 miles upstream near Whitehorse, Yukon Territory, Canada.

KOCAN: "And what we found was that as they enter the river as they return to spawn, about 30 percent of the fish were infected. But they didn't show any signs of disease. As they moved up the river, by the time they got to Tanana, about 20 percent of the fish showed clinical signs of disease. And this is where Bill Fliris was seeing these sick fish. By the time they reached Circle and Dawson, all of the infected fish, for all practical purposes, showed clinical signs of disease. They had spots on their liver and in their meat and all over the place."

Kocan sampling salmon
Fish pathologist Dr. Richard Kocan, left, takes organ samples from migrating king salmon on the Yukon River. Kocan says infected salmon have white spots on their liver, heart or flesh. Photo courtesy Bill Fliris.  
Kocan says it's likely the parasite has been lurking in king salmon since the late 1980s, and that it took several generations of salmon runs for the parasite to become well established. Scientists are concerned that these sick fish may die before they reach their spawning grounds. If true, it would help explain why king salmon stocks have crashed on the river.

KOCAN: "It's probably not the major cause, but I think it could be a contributing cause. This is a hypothesis, but if we're correct that these fish are dying before they reach the spawning grounds, and they are not spawning—then this could mean that for at least the last ten years they may have had 30 percent fewer fish on the spawning grounds than they predicted."

This summer, Kocan and researchers from the United States Fish and Wildlife Service plan to examine salmon on the spawning grounds along the upper Yukon. Meanwhile, other questions remain, such as how the salmon became infected in the first place.

KOCAN: "We don't know. They could be infected either in freshwater before they leave, or they could be infected when they're at sea."

Not everyone believes disease is to blame for the crash. Gene Sandone, regional supervisor with the Alaska Department of Fish and Game, says chum salmon runs on the river—which have much lower rates of infection—also have plummeted, and that salmon stocks throughout western Alaska are in trouble.

SANDONE: "We know for sure that the parent years of these salmon returning—both king and chum—were good. Now we're seeing extremely poor production from these parent years, and the one thing we can point to is poor ocean survival. We don't think it's a problem within freshwater. We think the problem is out in the ocean."

Sandone says because of the river's salmon declines, his agency may restrict king salmon harvests for subsistence food, and that there likely won't be any commercial fishing on the Yukon River this summer.

OUTRO: This is Arctic Science Journeys Radio, a production of the Alaska Sea Grant Program and the University of Alaska Fairbanks. I'm Doug Schneider.

Audio version and related Web sites
Thanks to the following individuals for help preparing this script:

Bill Fliris, Yukon River fisherman
Tanana, Alaska
Phone: 907-366-7245

Dr. Richard Kocan, Professor
Aquatic and Fishery Sciences
250 Fisheries Teaching/Research Bldg.
University of Washington
Seattle, WA 98105
Phone: 206-685-2984

Gene Sandone, Regional Supervisor
Arctic-Yukon-Kuskokwim Region
Alaska Department of Fish and Game
Anchorage, Alaska
Phone: 907-267-2115

Dan Albrecht, Executive Director
Yukon River Drainage Fisheries Association
725 Christianson, Suite 3B
Anchorage, Alaska 99501
Phpme: 907-272-3141
Fax: 907-272-3142

Jude Henzler, Executive Director
Bering Sea Fisherman’s Association
725 Christianson, Suite 3B
Anchorage, Alaska 99501
Phone: 907-272-3141
Fax: 907-272-3142

Dave Daum, Fisheries Biologist
U.S. Fish and Wildlife Service
Fairbanks, Alaska
Phone: 907-456-0219

Arctic Science Journeys is a radio service highlighting science, culture, and the environment of the circumpolar north. Produced by the Alaska Sea Grant College Program and the University of Alaska Fairbanks.

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Related Web sites

Marine parasite infects Yukon River king salmon (Anchorage Daily News 1/28/04)

2004 Ichthyophonus Final Report to U.S. Fish and Wildlife Service Office of Subsistence Management

Alaska Wildlife Notebook Series

Drawings of Alaska fish species