ink salmon are booming. That’s great for humpies, but perhaps not so great for every other species of salmon in Alaska. Indirect evidence suggests competition among species may have been compounded by the changing ocean climate, but the case is far from closed.

“There’s a lot of evidence that abundant pink salmon in the North Pacific are having ecosystem-scale impacts that include changes in the growth rates of different salmon populations of different species from different places,” says NOAA scientist Nate Mantua, based on a review of the scientific literature, including the work of Gregory Ruggerone.

Ruggerone, former president of Natural Resources Consultants, has been researching the relationship between pink salmon and other species for about twenty years thanks to pinks’ biennial life cycle.

“In most regions, they’re highly abundant in odd-numbered years and less abundant in even-numbered years,” Ruggerone explains. “That biennial pattern, it’s an incredible tool for testing the hypothesis that salmon compete with each other in the marine environment because climate and physical oceanography typically do not vary biennially, and most marine species do not have a two-year life cycle like pink salmon.”

The complicated life history and diversity of Pacific salmon species, which typically spend one or two winters in fresh water and two or three years in the ocean, can mask what Ruggerone calls the pink salmon effect.

All species of salmon in the Pacific are generalist predators, leading to an overlap of diets. Pink salmon diets overlap the most with sockeye, also known as red salmon, though both also catch small fish and squid eaten by coho and chinook.

Ruggerone’s work points toward competition for ocean food resources being a factor in limited salmon returns of sockeye in some regions and smaller sizes of adult sockeye returning overall. Year after year, he has documented how the biennial pattern of pink salmon has, in general, an inverse relationship with returns of other species. In even-numbered years, when pink salmon returns are lower, other salmon species tend to grow faster and survive better.

“The adverse effect of numerous pink salmon on vital rates of other salmon species has the potential to be far-reaching because salmon migrate long distances,” he writes in a 2022 publication titled “Are There Too Many Salmon in the North Pacific Ocean?” The paper explores his tipping point hypothesis, which states that “an overabundance of salmon, combined with effects of recent marine heatwaves, may have been responsible for unexpectedly low returns of all five species of Pacific salmon across the North Pacific in 2020.”

Mantua, who is the leader of the salmon ecology team at NOAA’s Southwest Fisheries Science Center and specializes in climate science, says that there is a lot of merit in the theory that the North Pacific’s carrying capacity for salmon—and other species that depend on the same food webs—has crested, based on the evidence presented by Ruggerone and the impacts of climate extremes in the North Pacific and the Bering Sea.

“We’ve had record-high ocean temperatures in a number of recent years that have come with widespread negative impacts on many different marine animals,” Mantua says.

Warmer water increases the metabolic rates of cold-water fish, such as salmon, which means they need to eat more food during warm years than they would in cold years to grow the same amount. Compounding this issue in the Gulf of Alaska are marine heatwaves that reduce food production at a time in salmon’s lifecycle when they need to rapidly grow.

“There’s evidence that those bad ocean conditions just from the climate and food web productivity side have been made worse in periods where you have really abundant pink salmon,” Mantua says.

The varying life cycles of salmon species mean that marine heatwaves affect them differently. Pink salmon have the most limited freshwater life, opting to quickly enter the marine environment, Mantua says.

“Their way of doing business is to overwhelm things with numbers and then grow really rapidly,” Mantua says. “The ocean is a great place for very rapid growth, if you can find food, and also a really dangerous place for extreme loss to predation.”

Pink salmon populations in the last thirty to forty years have been incredibly abundant compared to most of the 20th century, while other salmon populations have been struggling. The star exception to these trends is Bristol Bay sockeye salmon, which have seen record returns year after year.

“Bristol Bay sockeye are now in the sweet spot in terms of the warming of the North Pacific Ocean and the Bering Sea,” Ruggerone says.

However, recent historic returns in Bristol Bay don’t refute indirect observations about the interactions of pink salmon on sockeye, Ruggerone says. He explains that the strong growth and survival rates of Bristol Bay salmon in their first year in the marine environment in Bristol Bay and Western Alaska, where there are relatively few pink salmon, allows them to compete with pink salmon during the second and third years in the ocean. During these times, Alaska sockeye and Asian pink salmon habitats overlap in the subarctic North Pacific and the open waters of the central Bering Sea.

“Ruggerone’s work has shown how abundant pinks, largely Asian pink salmon from Russia, tend to come with much-reduced growth rates and size of adult ages for Bristol Bay sockeye salmon,” Mantua says. “Other work has shown that the abundance of pinks in the Gulf of Alaska looks to be impacting the productivity of sockeye salmon in the Fraser River [in British Columbia].”

Careful scale growth analysis done by Ruggerone and colleagues shows reduced growth rates during those periods of shared habitat use, Mantua says. In years of increased pink salmon abundance, sockeye salmon are growing less than in years of low pink salmon abundance.

“I have no doubt that they impact Bristol Bay sockeye salmon, as we have described in a number of peer-reviewed journal articles,” Ruggerone says.

Ruggerone’s method of using the biennial trends of pink salmon offers a glimpse into the ocean environment that is often referred to as a “black box” when it comes to understanding what happens to salmon during that period of their life cycle. While he is confident in the evidence teased out from the pattern, other salmon experts have yet to bite.

Katie Howard, the head of the recently established Salmon Ocean Ecology Program in the Alaska Department of Fish and Game, is less sure about the correlation between even- and odd-numbered years of pink salmon. Nonetheless, she says that Ruggerone’s and his colleagues’ work is incredibly important.

“He’s looked at so many salmon stocks all over North America, which is really important for setting the stage for further research,” Howard says, noting that her program’s goal is to build on that foundation and provide more clarity through direct observations. “For most salmon species, most of their life is occurring in the ocean and we just don’t have that much information about what happens in the ocean with the salmon,” she says.

Without the rich data that scientists have on the freshwater lives of salmon, Howard says fundamental questions become hard to answer: What has the greatest effect on salmon mortality in the oceans? Should that change how salmon stocks are managed? What about changes in climate?

“Those kinds of questions are really hard when there’s so little information and observations of salmon in the ocean,” Howard says. “It’s really hard to tease apart what’s happening with pink salmon from what’s happening more broadly with the marine heatwaves… because all the things are happening at the same time.”

Howard says she’s worried that by remaining salmon-centric in their approach to understanding what’s happening to salmon in the high sea, scientists could be missing the big picture.

In a presentation to the Alaska Board of Fisheries Hatchery Committee, Howard stated that barriers to accessing scientific work in non-English journals is one blind spot. She also suggested that other two-year patterns could, in part, explain the correlations currently blamed on pink salmon.

“That’s part of the reason why we’re trying to approach this question in some different ways,” Howard says.

Howard is one of sixty international scientists taking part in the International Year of the Salmon. The program was developed to further the scientific understanding of the ocean phase of the salmon lifecycle to improve efforts to assess, forecast, and manage salmon.

Central to this is addressing if marine heatwaves affect the carrying capacity of the North Pacific ocean, explains Ed Farley, who manages the Ecosystem Monitoring and Assessment Program with NOAA Fisheries in Juneau.

“I think we can at least address the central goal on that question,” says Farley, who spent the winter on the NOAA research vessel Bell M. Shimada as part of the 2022 Pan-Pacific Winter High Seas Expedition.

Collecting data during winter months was critical to the multi-year project. It has rarely been done due to harsh weather, yet winter is one of several opportunities for salmon species and stocks to intermingle. A leading hypothesis is that fish that didn’t forage efficiently and grow during spring and summer may be more susceptible to mortality during winter. That is yet another question in need of direct evidence rather than observed correlations.

Data collection for the International Year of the Salmon occurred in 2019, 2020, and 2022. During that span, a marine heatwave peaked and waned, “So we’re going to be able to see how fish are responding in terms of their shifting distributions,” Farley says.

Farley explains that further analysis of the data collected should help scientists make direct observations of the fitness level of fish between warm years and colder years. Unfortunately for researchers, and to their surprise, the 2022 survey caught far fewer pink salmon than they expected.

“We’re not finding pink salmon where there are other salmon,” Howard says. “So what does that mean, in terms of competition? We’re still trying to figure that out.”

Farley points out that research vessels weren’t able to go as far southwest of the Aleutian chain as they would have liked.

“There’s a large area there that is salmon habitat that wasn’t sampled, and that’s unfortunate,” he says.

The lack of pink salmon samples means that the project might shed light on many aspects of the lives of salmon when stocks and species are mixing in the high sea, but the role of the vast volumes of pinks might remain veiled.

“Whether or not that means pink salmon were competing or out-competing is hard for us to say because we just didn’t catch that many of them,” Farley says.

Nonetheless, the pan-Pacific data collected should provide a baseline for many of the other questions scientists are attempting to answer.

Farley also remains optimistic about Alaska’s salmon fisheries, despite some of them shifting.

“Sometimes we get discussing these things and people think this is the end, you know. In my opinion, it’s not the end,” Farley says.

If pink salmon are outcompeting other species and adapting better to changing ocean conditions, there are economic implications for the fishing industry.

The first wholesale value of all species of salmon in Alaska was valued at about $1.7 billion in 2019. For the last four or five years, sockeye salmon have comprised 50 to 65 percent of the total value of Alaska salmon harvests, while pinks have made up only about 10 to 25 percent

In 2019, 48 percent of salmon purchased were Alaska pink salmon, but on a value percentage, it was only 19 percent. The opposite was true of sockeye, which comprised 33 percent of the total volume but 65 percent of the total value, explains Dan Lesh, a seafood industry specialist at McKinley Research Group.

A significant part of the difference in value versus volume between the two species comes from a large portion of sockeye being sold as fillets or whole fish. In contrast, nearly 50 percent of pink salmon is canned, and nearly none of it is sold in the form of higher-market value whole fish or fillets. This has a lot to do with the marketability of the more classic “salmon” colored flesh of sockeye, which is known to be better for fillets and portioning.

International Year of the Salmon

“On the statewide level, especially when you look at the booming sockeye harvest in Bristol Bay, you can imagine we’re going to be okay,” Lesh says, before pointing out that those booming returns are only beneficial to fishermen and processors in that area.

When the data is broken down into smaller regions and individual gear types, it’s possible to see where people in the seafood industry are getting hit the hardest.

“The gill net fleets [in Southeast and Southcentral] are struggling, whereas the seine fleets are doing better because they can focus on those pinks,” Lesh says.

While a future in which pink salmon dominate Alaska waters is far from certain, Lesh sees the benefits in fishermen and processors starting to plan how they might adjust to such a change.

“My mind goes to some of the adaptive levers we could pull,” Lesh says. “We could focus on quality; we could develop markets.”

Traditionally, pink salmon has been a volume market, while the sockeye fishery has seen significant efforts over the last decade toward quality improvements. Some sockeye specialists have developed direct marketing models and subscription boxes—markets that demand premium quality.

“If you’re relying on pink salmon, you could see improvements in quality boosting the market price,” Lesh says. “I think there’s some reason to think that would be successful in the market.”

While some scientists are more swayed than others about the possibility that pink salmon are compounding the effect of marine heatwaves, all of them agree that more research is necessary.

“We’ll see what happens,” Ruggerone says. “The ocean conditions are always dynamic.”