Besides supporting fishermen, salmon are a keystone species in Alaska and the Pacific Northwest, supporting wildlife from birds to bears and orcas.
Mary Ruckelshaus, a federal biologist with the Northwest Fisheries Science Center in Seattle, has been running climate models to peer into the future for Pacific Northwest salmon. Those models predict that salmon will become extinct without aggressive efforts to preserve the clear, cool streams needed for spawning, such as planting trees to shade streams and curtailing the amount of water siphoned off by farmers.
"It's sort of a time bomb," Ruckelshaus said.
"If people don't have a plan for it, it can be disastrous when it hits."
Her models didn't factor in the potential for emerging diseases, such as the one that Kocan, her former professor, has been studying.
Kocan views Ichthyophonus as a classic emerging disease. He pointed out that salmon, a lucrative catch, had been scrutinized by scientists and fishermen for decades, and the disease had never before been reported. In the last decade, it has shown up in salmon on the Yukon, Kuskokwim and Taku rivers in Alaska and on various rivers in British Columbia and Russia.
It has also been detected in recent years in rockfish and smaller noncommercial fish in Puget Sound and elsewhere off the coasts of Oregon and Washington, and in freshwater trout on Idaho farms.
It's the kind of redistribution of disease that can be expected with climate change, Kocan said: "Everything is getting warmer, and that's how climate change is going to redistribute all kinds of disease. Parasites have their optimum conditions -- upper and lower limits. We'll notice where they show up but not necessarily where they disappear."
Ichthyophonus is among a class of ancient parasitic microbes that can move fast, taking advantage of new niches using age-old tricks that have kept them around for billions of years.
None of this comforts Pat Moore, a musher with dozens of dogs, and others who rely on the bounty of the Yukon River to make their living. It's a culture that lives on the edge and cannot stomach waste.
"I don't want to kill fish for the sake of killing them," said Moore, as he expertly sliced a king into narrow strips.
"I want to use the damned things."