Yukon Salmon Infected by Warm Water Parasite

Yukon salmon have become infected by a parasite never before seen in wild salmon. Warming Arctic temperatures, producing 65 degree F water at the mouth of the Yukon River provide conditions favorable for growth of "white spot" parasite Ichthyophonus hoferi.
The parasite weakens the salmon and makes the flesh unsuitable for human consumption by fouling its flavor. This parasite was never found before in salmon because salmon is a cold water fish. The warming arctic has provided new habitat for this parasite.

By Environment Canada

Salmon provide a livelihood for traditional Alaskan and Canadian fisherman while concurrently supporting the ecosystem by providing food to large predators. However, in the 1980s a warm water parasite first appeared in the Yukon. Since then the parasite has become much more widespread in the salmon populations now affecting about 25%  - 30% of the fish at the river mouth and mid river. Global warming appears to be the culprit.

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 over the last three decades. The warming began earlier each spring, following 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.

Unhealthy salmon aren't making it to the spawning grounds 2200 miles upstream. Unhealthy fish apparently aren't strong enough to make the swim.

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

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

Tracking what happens to these fish is difficult. The Yukon turns mocha-brown in the summer, when its swift waters carry a load of rock flour released by rock-pulverizing glaciers and other sediment. Salmon that perish sink out of sight.

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. "He's not going to do very well."

The strongest fish are reproducing,but in diminished numbers.

This parasite creates even more problems for Fisheries and Oceans Canada, as biologists there are already trying to cope with lower than normal salmon runs in the Yukon River. In 2000 only about 12,000 chinooks made it back to their spawning grounds, a number far below the department's goal of 28,600 fish.

The loss of fish is threatening the way of life of the indigenous people, but their dogs are well fed.

By LATimes

There are so many tainted fish that the dogs can't eat them all.