This year in Bristol Bay, fishing crews have noticed that sockeye salmon were on the small side — an observation confirmed this month by the Alaska Department of Fish and Game.
Fish and Game officials say that at this point in the 2024 season, the sockeye returning to Bristol Bay are on average the smallest they’ve ever seen. This continues a decades-long trend.
So far, the average weight of Bristol Bay sockeye was 4.2 pounds this year. Fish and Game biologist Stacy Vega said that’s the smallest average weight on record.
“Fish are smaller, weigh less than, than they have in the past and against our historical averages,” Vega said.
The exact number could change a bit by the end of the season, but Vega expects it will stay low. That smaller fish size also means a smaller overall catch. By mid-July, Vega said, fishing crews had hauled in almost 130 million pounds of fish. That’s almost 70 million pounds less than this time last year.
Vega said that all kinds of factors go into fish size. The same is true with humans. Age is the most obvious: The tallest toddler is still shorter than the shortest teenager.
But other things also matter: How tall were your parents and grandparents? Did you grow up with enough to eat, or did you experience hunger? And then there are the less obvious things. Over many generations, hotter or colder climates can also impact our body size.
As with humans, so with fish.
“There is nature and nurture to all things that grow,” Vega said.
“Different water temperatures mean not just availability of different food types, they also mean how well you metabolize that food. So temperature, food, wind, currents — there’s so many things that go into how fish grow and how old they get,” she said.
This year, Vega said, the biggest factor for returning sockeye was their age.
“So what we’re seeing here as an overall decrease in weight of fish is a factor of a lot of young fish coming back this year,” she said.
Most of the fish that came back this year are fish that spent one year in the lakes and two years in the ocean. But not all of the fish that came back were the same age. Fish and Game tracks four major age classes. This year, as of July 18, each age group is the smallest they’ve seen, compared to historical data that goes back to the 1970s.
Almost three-quarters of the fish spent one year in the lakes, then two years in the ocean. That age class weighed 3.9 pounds on average. Similar fish that stayed in the ocean an extra year came back heavier, at 5.3 pounds on average.
A smaller group of fish spent an extra year in the lakes before swimming out to the ocean; those fish were just a tenth of a pound heavier than their counterparts, at 4 pounds for fish that stayed in the ocean two years and 5.4 pounds for fish that stayed for three.
For each of those four age classes, Vega said, “We saw the smallest and lightest size of fish we have ever seen in our history. Not by a huge margin — it’s not pounds and pounds — but it definitely is the smallest we’ve ever seen. 2020 was a close second.”
Since 2015, Vega says, more fish have been returning on average. One hypothesis for smaller fish sizes is that when more fish survive early on, there’s less food to go around as they grow. Each fish gets less to eat, and they grow up smaller.
“Ocean conditions, lake conditions, food availability — all that factors into the size of fish and how many return. So it’s all intertwined. But certainly with really big runs we see smaller fish,” Vega said.
And sockeye aren’t just competing with each other. They’re also competing with other species, like pink salmon. Greg Ruggerone, a scientist at the University of Washington, has been testing the hypothesis that pink salmon affect the annual growth of sockeye salmon in the ocean.
Researchers can’t remove all the pinks from the ocean to see what happens to sockeye. But they don’t have to. Because something similar happens naturally: every other year, the number of pink salmon skyrockets.
“Because they have a biennial pattern of abundance: very high abundance and odd numbered years and lower abundance and even numbered years. Sometimes, in some regions, that difference is 25 times more abundant in odd numbered years,” Ruggerone said.
Unlike sockeye, pink salmon stay in the ocean for a set number of years: Odd year and even year populations don’t usually mix. Over the years, one of those populations got big, and one stayed small, so every other year, sockeye have more competitors.
Ruggerone suspected that those competitors might have an impact on sockeye size. With Peter Rand of the Prince William Sound Science Center, Ruggerone analyzed sockeye from the Gulf of Alaska and from Egegik in Bristol Bay for a study in the ICES Journal of Marine Science.
Ruggerone says the data suggest that all of those pinks are indeed having an impact on sockeye size.
“In odd-numbered years when pinks are very abundant, the growth was low. And in even-numbered years, when there were fewer pink salmon, growth during the second and third years at sea was relatively high,” Ruggerone said.
Ruggerone said that pattern is just oneof many factors that made this year’s sockeye smaller. But he said it’s an important factor to keep an eye on, because the number of pink salmon has been growing over time.
Partly, that’s because of hatcheries. But it’s also because wild pinks have been doing really well.
“Going back to the early 1950s, there’s a very strong correlation between pink salmon abundance and the ocean heat index,” Ruggerone said. “Pink salmon are climate change winners.”
Sockeye have also been doing well in terms of the number of fish, despite their shrinking size. But for other salmon species, that abundance of pinks may be a bigger problem. Ruggerone says that complicates traditional management wisdom.
“Fisheries managers, we’re taught to promote abundance in the wild populations, so that there are more fish for fishermen to catch. But here’s a situation where the pink’s are doing extremely well with climate change, and other species are not doing so well,” Ruggerone said.
Now, he says, some people are beginning to question whether maximizing wild pinks for future abundance is still the right approach.
Ruggerone said there will be fewer pinks next year, so sockeye will have less competition for food. Plus, many sockeye that did not come back this year will see another birthday, so Vega said Alaska fishers can also expect more older fish. Both factors may mean larger sockeye next year in Bristol Bay.
