Chinook salmon returns to the Yukon River are so low, even subsistence fishing is on hold. Managers are closely watching average swim speeds and when Chinook salmon are expected to arrive in each district.

Even with 60 years of Yukon data, it’s a tough run to track because the timing is so unpredictable.

“They brought me up there in the first place because the timing jumps around so much. The midpoint of the run can be June 10th or July 1st. So that makes it a very nervous business when you’re trying to manage the fishery. Plus, most of the run goes through in just over two weeks.”

Phil Mundy is a former longtime director of NOAA Fisheries’ Auke Bay lab in Juneau. He’s studied Alaska salmon since the 1970s. But it was Yukon elders who taught him how to fine tune the run timing.

“So I asked them and they told me the wind blows the fish in the river- everyone knows that, young man. And I wondered how that works. “

Cook Inlet fishermen told Mundy the same thing about sockeye salmon.

“They said you know, it’s when the wind blows and you get the biggest time closest to July 17. Everyone knows that. So I started looking into it.  We couldn’t figure out exactly how the wind was doing what it did. I didn’t think the fish put up their dorsal fin like a sail to blow into the river, but there had to be something there because they seemed to be right.”  

It took until 2006 to figure out the mystery.

Mundy saw a scientific article that talked about how salmon make the change from going from fresh to salt water and vice versa.

“There’s this thing called a calcium ion switch, and it is triggered by alternating exposure to different salinities.”   

Young salmon can’t swim straight into salt water because it will kill them; it’s the same for adults  in the ocean returning to their home streams. They have to have alternating exposure to different salinities.

“I used to count fish from airplanes,  and I’ve seen this at Bristol Bay and at Cook Inlet where you get the river water piling up against the marine water on the river plume, and then you’ll see the salmon weaving in and out along the edge of the front between the fresh water and the salt water. And I never knew why they were doing that.  They will pile up if there is no wind to mix that fresh and salt water to make it brackish. If there is no wind to blow, they will pile up on that front until some other trigger, which we probably don’t understand, sends them all in.”

At the Yukon, Mundy says the wind mixing the water even trumps early ice melts as the best indicator of the salmon arrivals  –

“We know now that it really depends on whether or not they are getting a good strong forcing wind across the delta that hits the marine water and mixes that fresh water in with the salt water.

Today, he says satellite data on salinity and more from the Alaska Ocean Observing System make predictions easier and more reliable.