Alaska's sick salmon

TANANA, Alaska —

With a sickening thud, another hefty and handsome salmon lands in the waste barrel, headed for the dogs.

"See, it's all of the biggest, best-looking fish," said Pat Moore, waving a stogie at the pile of discards. "It breaks my heart. My dogs cannot eat all that. The maggots will get them first."

More Alaskan salmon caught in Tanana end up in the dog pot these days, their orange-pink flesh fouled by disease that scientists have correlated with warmer water in the Yukon River.

The sorting of winners and losers at Moore's riverbank fish camp illustrates what scientists have been predicting will accompany global warming: Cold-temperature barriers are giving way, allowing parasites, bacteria and other disease-spreading organisms to move toward higher latitudes.

"Climate change isn't going to increase infectious diseases but change the disease landscape," said marine ecologist Kevin Lafferty, who studies parasites for the U.S. Geological Survey. "And some of these surprises are not going to be pretty."

The emergence of disease in Alaska's most prized salmon has shocked fishermen and fisheries managers. Alaska's wild salmon has been an uncommon success story among over-exploited fisheries, with healthy runs and robust catches.

Fishermen and regulators who have cooperated to save species from overfishing and local environmental hazards are unprepared to deal with forces beyond their control: How to manage a fishery for climate change.

The return of the king — or chinook — salmon is eagerly anticipated along the Yukon.

Savvy buyers from Japan converge on the docks near the river's mouth to purchase these fish that have bulked up with extra fat to swim more than 2,000 miles, across Alaska, to spawn in the stream of their birth.

As a defender of the fish's reputation, Gene Sandone, a regional supervisor for Alaska's Fish and Game Department, was less than receptive to complaints from Tanana fishermen, including Moore, that something was wrong.

The chinook they pulled from the Yukon River about 700 miles inland didn't smell right. The flesh turned mealy. The salmon didn't dry right in smokehouses, either. Instead of turning into rich red strips of salmon jerky, the fish turned black and oily. "If you don't weed out the bad ones, it'll stink up the whole smokehouse," Moore said.

Salmon jerky strips are a staple among the American Indians and subsistence fishermen in rural outposts such as Tanana, a village of 270 people. "It'll keep you warm in the winter," said Lorene Moore, Pat's wife and a native of the village. In Alaska's bigger cities, the jerky fetches $20 or more a pound.

UW expert consulted

In the late 1980s, a lab at the Center for Fish Disease Research at Oregon State University identified the problem as "white spot disease," caused by a microscopic parasite, Ichthyophonus hoferi. "Ich" (pronounced "ick") is a well-known disease, harmless to humans, that was blamed for devastating losses in the herring fishery in Scandinavia.

The portion of Yukon salmon with ich grew each year. Fishermen were throwing away up to 30 percent of their catch, forcing them to catch more fish.

"The Alaskan Department of Fish and Game wasn't interested," said Bill Fliris, another Tanana fisherman. "They said, 'There's no money to study this. It's a natural disease. There's nothing we can do about it.' "

So Fliris contacted Richard Kocan, a fish-disease expert at the University of Washington. Kocan began to test the fish in 2000, the same year the king salmon run suffered an unexpected temporary collapse that forced the closure of the river's commercial fishery.

At the mouth of the Yukon, where the commercial gill-netters operate, nearly a third of the chinook salmon were infected, Kocan found. But the fish usually did not show signs of the disease.

The same proportion was infected at midriver near Tanana, about halfway to the Canadian border.

Kocan went upstream to the spawning grounds near Whitehorse, Canada, and found the proportion of infected fish plummeted. It didn't seem logical that the fish were recovering during the last part of their 2,200-mile swim, accomplished over many weeks without eating.

"The working hypothesis, is that they died before they made it to the spawning grounds," Kocan said.

To test his theory, Kocan set up a laboratory experiment that compared the swimming stamina of infected rainbow trout with that of healthy trout. He used a chamber with water swift enough to exhaust a healthy fish in about 10 minutes. The infected fish lasted about two minutes. "It's like asking someone with heart disease to run a 10K race," Kocan said.

A key question

That left a question: Why did the previously undetected disease show up in the late 1980s and resurface every year since?

Kocan and his students scrutinized all the potential variables and found only one significant change: Average river-water temperatures had been rising in the past 30 years. The warming began earlier each spring, after an earlier breakup of the river's ice. The June temperatures showed the greatest increase, about 6 to 8 degrees warmer, and June is when king salmon return from the ocean and begin their long upriver migration to spawn.

Unlike warm-blooded animals, the body temperature of salmon fluctuates with the temperature of surrounding waters. Laboratory studies of ich infections in trout, a close cousin, have revealed that the incidence of disease and death rises as water warms, especially above 59 degrees.

Kocan spent five summers on the Yukon River studying the parasite, creating an uproar among fishermen by sharing his findings directly with them, rather than allowing state Fish and Game officials to review the data first.

Kocan thinks up to 20 percent of king salmon are dying en route to the spawning grounds. If so, fisheries managers would have to cut the commercial catch by at least that amount to keep the run healthy.

Sandone, the regional Fish and Game supervisor, thinks the sick fish, weakened by the parasite, swim along the slower-moving edge of the river, where a disproportionate number get caught by fishing nets and fish wheels that line the banks.

In other words, subsistence fishermen like Pat Moore are simply catching most of the sick fish. The healthy ones swim just out of reach, deeper in the river, headed straight for Canada.

"That's my theory: that they are not dying on the way," Sandone said. "Even if they are dying on the way, so what?" His department limits the catch based on how many fish make it to the spawning grounds to reproduce. That's been going well, he said, except for last year, when the number of fish that made it to Canada fell 50 percent below the minimum spelled out in a U.S.-Canadian agreement.