How A Parasite Is Causing Yukon River Chinook To Die Before They Can Even Spawn

With salmon struggling up and down the Pacific coast, from California through the Pacific Northwest, British Columbia, and into Alaska, a deadly parasite is taking down Yukon River king salmon even before the fish can spawn. Coho salmon in Washington waters have also been affected by prespawn mortality syndrome, an issue our sister publication Northwest Sportsman has reported multiple times. Yet in the case of the Washington fish, it’s been particles finding their way into streams. The Alaska issue in the Yukon, which has seen stocks crash in recent years, is a specific parasite wreaking havoc on the watershed.

Here’s more from Science magazine:

These juvenile fish at the U.S. Geological Survey’s (USGS’s) fisheries laboratory here don’t realize this is a deadly treat, containing a single-celled fish parasite called Ichthyophonus. The meat came from parasite-ridden Chinook salmon pulled from Alaska’s Yukon River, where salmon numbers have plummeted in recent years—and Ichthyophonus infections, together with rising temperatures, are a prime suspect.

In the coming weeks, the parasite will spread throughout the fish’s bodies. White nodules resembling tiny flakes of salt will form on their hearts, disrupting their ability to beat properly. Muscle tissue will wither. Eventually, some will die from the infection.

Barcelona hopes this gruesome fate will help answer crucial questions about what’s led to dwindling runs of Yukon Chinook salmon, once a mainstay for communities along North America’s fifth largest river system, and how to manage them going forward. Salmon runs have fallen across much of western Alaska, but the Yukon Chinook are hardest hit. The fish are so depleted that Alaskan and Canadian officials last year agreed to a first-ever 7-year ban on nearly all fishing for Chinook in the river and its tributaries, a Texas-size watershed spanning both countries.

The piece, which is a very compelling read, suggests that warming water temperatures on the Yukon have given the parasite more opportunity to overpower the salmon, a variable that has been a major talking point for Pacific salmon struggles.