Back in the 1970s, Peggy Kormendy recalls pulling an 84-pound chinook salmon from the Yukon River. It was a massive haul, a once in-a-lifetime event that’s probably going to become even less likely from here on out. Salmon were just bigger and healthier then, the Tr’ondëk Hwëch’in First Nation Elder told The Narwhal. Now salmon tend to be about 10 to 15 pounds.

"When we were fishing, they were in good shape," Kormendy said. "Then, the fish were getting smaller … I don’t know why."

Recent research comes closer to an explanation. Four species of salmon are indeed getting smaller, largely a result of them spawning at a much younger age, according to a joint study conducted by researchers at McGill University and U.S. schools and government departments.

Researchers say there are two main reasons behind this shift: climate change and competition in the ocean.

Peter Westley, co-author and researcher at the University of Alaska Fairbanks, said this work bolsters what Indigenous people have observed. "There’s agreement, there’s no question: the fish are much, much smaller," he said.

Chinook salmon in particular, Westley continued, have taken the biggest hit in Yukon, declining in size by nearly 20 per cent in some areas over just a few decades.

He said fish that have spent upward of six years in the ocean are increasingly missing from Yukon rivers. Instead, salmon are returning to spawn at a younger age, such as chinook that historically mature in the ocean for about seven years but are now returning to spawn after just four. And the fast-maturing fish aren’t growing to the same size of their forebears.

"How big a fish is shapes the way it interacts with the world around it," Westley said "It influences things like, for females, how many eggs and how large an egg a female can carry around and produce, which, in turn, influences the population viability of future generations."

Warmer ocean waters see smaller, younger fish entering river systems

Researchers focused on four species of Pacific salmon — chinook, chum, coho and sockeye — and found that each were smaller in size after 2010 than those observed before 1990.

There were patterns for species across several regions, the study says, noting that chinook salmon decreased in length by an average of eight per cent, the greatest rate of decline compared to other species. That decrease jumped to 10 per cent in the Yukon River system in particular. (Female chinook salmon now produce 16 per cent less eggs on average — a troubling result for the dwindling chinook population.)

As well, coho decreased in length by 3.3. per cent, chum were 2.4 per cent smaller and sockeye saw a 2.1 per cent decrease in length.

In order to calculate the change in salmon sizes, researchers parsed through six decades’ worth of size and age data for 12.5 million salmon, collected by the Alaska Department of Fish and Game.

Westley said the drivers of these changes could point, in part, to climate change, specifically warmer sea surface temperatures and shifts in currents and atmospheric pressure, which could affect productivity, survival and the abundance of salmon.

"Changing ocean conditions that accelerate growth during the earlier years in the ocean will trigger earlier maturation for many individuals," he said. "As a general rule, fast growth results in earlier maturation."

There’s a paradox at play here, he added, with the largest fish being the oldest and slowest growing members of the population. And it’s those members that are increasingly lacking in Alaska’s rivers.

"We don’t know what aspect of climate is driving these changes, but it is highly associated with these changes," Westley said. "It’s the subject of future work."

Abundant hatchery and wild salmon species may be out-hunting others

All salmon go after similar food in the ocean, pitting them against each other in a race for sustenance. Researchers found a particularly troubling link between the size of sockeye salmon and the abundance of hatchery fish such as pink salmon, which the North Pacific has in droves.

"Our results provide further evidence that wild and hatchery-enhanced pink salmon abundance in the North Pacific has reached such high levels that they appear to be exerting an influence on ecosystem structure and function," the study says, noting that five billion hatchery salmon are released into the North Pacific every year adding to "already high abundances of wild pink, chum and sockeye."

A lack of quality food sources, due to this competition, could be contributing to the declining size of some salmon species.

The study says hatchery managers lack tools to assess the potential impacts of hatchery fish on wild populations that could inform their decisions around releases.

"I think the next step is bringing in information like ours and work meaningfully and honestly with managers and industry to think about the scenarios of different release levels," Westley said. "We net less benefit than we think with the release of hatchery fish and so we need to understand the real pros and cons of these activities in a way where everybody is around the table."

Salmon are of vital importance to Alaska’s economy. According to the study, fishermen in the small town of Bristol Bay, located in southwest Alaska, collectively made $214 million in 2017.

Westley said that a catch of smaller fish are worth less than a catch of bigger ones, even if they weigh the same overall.

"You have to work harder to make as much money as you did in the past," he said, "Size is profoundly important."

But there are other issues that go beyond keeping the fisheries in good health and state coffers buoyed, involving food security and cultural connections.

"Socioeconomic impacts of declining salmon size have long been of concern for Alaskans, especially those whose well-being, food security, and economic livelihoods depend on salmon," the study says.

How to support healthy salmon populations

The research shows that habitat protection alone isn’t enough; more work needs to be done to understand what salmon are facing across multiple regions, Westley said.

"We need to be expanding our thinking beyond simple numbers," he said. "We’re really good at counting the fish and we’re pretty good at measuring fish, but we’re not as good at managing for diversity of different fish sizes and ages."

And that diversity is important both for the health of the ecosystem and for people who rely on the salmon, he said.

"It seems like we’re losing diversity, despite the fact of working really hard to protect habitat that we know gives us that diversity," Westley said. "It’s daunting, but it’s an eye-opener."

As for Kormendy, she wants people to leave the salmon that swim up the Yukon River, to spawn, alone. Catching them, she said, prevents future generations of fish from making their way to the ocean, and deprives First Nations culture of their right to those fish in years to come.

"I’m 83 now, and I think about my grandkids," Kormendy said. "We have to think about our future down the road. Salmon’s really important to Native people. We have to put our concerns forward."