There’s something unusual going on with the sockeye salmon runs returning to Alaska this year. In some places — like Bristol Bay — the runs are strong. In others, like the Copper River or the Kenai River they’re unexpectedly weak. In some places, there are sockeye that are unusually small. In others, sockeye of a certain age appear to be missing entirely.
It’s a mystery.
In Southeast Alaska, one of the first Alaska Department of Fish and Game staffers to notice an unusual trend was Iris Frank, a regional data coordinator and fisheries technician.
Frank’s lab is on the first floor of fish and game’s Douglas Island office that looks like it hasn’t changed much in the 32 years since she got there.
Frank has been looking at blown-up images of sockeye salmon scales for decades. She pops one onto the machine and dials it into focus to show that salmon scales have ridges, called circuli. They look a lot like fingerprints.
Circuli carry a lot of information about what a salmon has been doing since it hatched.
“So if you think about a fish being out say, in a lake in the summertime, it’s warmer there. There’s more feed around. So these circuli are probably going to be bigger and more widely spaced apart,” she said.
Then, during the winter months, the ridges compress together. Group those two sets of ridges together, Franks says she can usually get a pretty good idea of how old a salmon is from reading the scales.
She gets about 40,000 of these salmon scales in a year and she’s an expert at reading them. In the last few years — she’s noticed that on some fish — those lines are getting closer and closer together. Frank is quick to point out that she is not a fisheries scientist, but that could mean the fish aren’t growing as fast, or as big as they normally do.
She said she hasn’t seen anything like it before, in the decades that she’s been reading scales.
“This is just, you know, the hairs on the back of your neck standing up going ‘well that’s really odd,'” she said.
Frank doesn’t know why it’s happening, or what it means. But it’s a clue.
And, it’s part of a pretty big mystery. Elsewhere in the state, fish and game scientists are scratching their heads over smaller sockeye, sockeye trickling into rivers and lakes where they normally come back strong or whole age groups of sockeye that appear to be missing. Several said they’re wondering what is happening to the sockeye once they leave Alaska’s freshwater and head out into the ocean.
Out at the Alaska Fisheries Science Center in Auke Bay, there’s a team of National Oceanic and Atmospheric Administration scientists who specialize in researching fish at sea.
Among them is Ed Farley. He’s a program manager for the Ecosystem Monitoring and Assessment Program. There, researchers focus on Alaska’s large marine ecosystems like the Gulf of Alaska and the Bering and Chukchi Seas.
Farley said he was not surprised to see inconsistent returns of sockeye salmon to Alaska this year, and he has a pretty good idea of what could be happening — though he’s reluctant to call it a smoking gun.
One big clue is the blob. That’s the warmer-than-normal water that moved into the North Pacific about four years ago. It stayed unusually hot through 2016 in the Gulf of Alaska shelf — some 4 to 6 degrees higher than normal. Farley said that shelf is where young sockeye salmon from Alaska go to eat once they venture out from their home rivers. Generally they move onto the shelf and move counter-clockwise foraging for food before they wind up in the North Pacific Ocean.
That heat has a big impact on salmon and other cold-water species.
“That’s going to increase their metabolic rate, so they’re going to have to find more food,” Farley said.
But something else happened in the Gulf of Alaska during that time period too.
Farley said a team of researchers did surveys on the food web during those hot years and found that some of the key food for young sockeye salmon was missing.
Some things like copepods — that’s a high-fat bug that sockeye eat, basically eggs with legs — just weren’t around in the same volume as they had been.
“So you kind of a get a double whammy,” Farley said. “You know they’re having to eat more because their metabolic processes are speeding up. But there’s less prey. And so this is impacting their growth rate at this time, this period of summer, when they’re supposed to grow and get this fat store.”
Farley said that could have caused a lot of young sockeye salmon to die during their first summer at sea.
Another factor, Farley said, is pink salmon. There’s some evidence that they compete with sockeye for food in the North Pacific. But Farley is quick to point out that the role pink salmon play in sockeye salmon deaths is still in question.
Farley also works with the North Pacific Anadromous Fish Commission which has scientists from several countries including Russia, Japan and the United States. Farley said some researchers on that commission have looked at sockeye salmon scales and calculated growth rates of the salmon during different life history stages. They’ve found a pattern of growth that shows sockeye salmon aren’t growing as fast in years when there are a lot of pink salmon in the same place.
But when it comes to the sockeye salmon returns this year, Farley is less focused on what’s happening in the North Pacific and more on the Gulf of Alaska. He suspects that some of the sockeye salmon returning to Alaska this year went out into the ocean at a time when they needed more food to survive and it just wasn’t there.
And those banner Bristol Bay sockeye salmon returns this year? Farley said those same warm ocean conditions might be the culprits there as well.
Warm water may have decimated the food web in the Gulf of Alaska — but there’s evidence that it made the Bering Sea more fertile. Farley says that’s where Bristol Bay sockeye rear, so they were much better off than their Gulf of Alaska relatives.