Marine heatwaves will cripple salmon, cod and pollock at twice the rate previously predicted, study says

Scientists suspect heat stress killed a large number of summer chum salmon migrating through the Koyukuk River, a tributary of the Yukon. The carcasses held underdeveloped eggs and sperm, indicating that the salmon were far from their spawning grounds, where salmon usually die. (Photo by Stephanie Quinn-Davidson/Yukon River Inter-Tribal Fish Commission)

Over the last decade, two massive marine heatwaves, better known as “blobs” swept the North Pacific Ocean, raising surface temperatures more than 5 degrees Fahrenheit causing blooms of toxic algae and major die-offs in the ecosystem. A new study from the University of British Columbia reports that as these heatwaves continue, they may have far more devastating implications to fisheries than previously predicted.

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Climate scientists have known for years that global warming would have devastating long-term impacts on marine species. Already, fast-melting Bering Sea ice is threatening spotted seals and other marine mammals. Warming Gulf of Alaska waters wiped out cod eggs in 2019, causing a crash in cod stocks. Record warm waters in the Yukon River last summer killed thousands of migrating salmon with heat stress.

While climate change is steadily warming oceans all over the world, marine heatwaves, like the two North Pacific “blobs,” are causing more dramatic swings in surface temperatures. In 2014 and again in 2019, ocean temperatures in Alaska rose as much as 5 degrees Fahrenheit.

A NOAA map illustrates the similarities between the 2014 “Blob” and the 2019 heat wave event in ocean temperatures (Map courtesy NOAA).

William Cheung, a professor at the University of British Columbia’s Institute for the Oceans and Fisheries said marine heatwaves will be frequent and that will double the damage to northeast Pacific fisheries.

“The normal now is cooler than the normal in the future, 50 or even 100 years later,” said Cheung. “Then on top of that, we add an additional few degrees Celsius. And so that would create additional challenges to fish stocks and fisheries.”

Cheung co-authored a report analyzing the impacts of marine heatwaves on Northeast Pacific fisheries. The study teased out the impacts of high-intensity heatwaves from the average effects of a warming climate over time.

The findings show that by 2050, marine heatwaves will double the impact to important fishery species like pollock, cod and salmon over previous predictions that only took into account the effects of climate change.

It’s an alarming forecast for Alaska, where seafood is a $5.6 billion industry and the state’s largest export, after oil and natural gas. Fisheries are the primary economic driver for coastal Alaskan communities, and carry a globally recognized reputation for healthy management, even as climate change threatens the futures of many essential stocks. According to Alaska Sea Grant, more than 100,000 Alaska Natives and non-natives in rural communities rely on healthy fish stocks for subsistence living.

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“It will lead to a variety of impacts on fish stocks, like a decrease in biomass, decrease in potential catches, changes in the distribution from where they are living now,” said Cheung.

The study says previous research “greatly underestimated” the risk to fish stocks in a warming ocean. For instance, prior studies suggested sockeye salmon stocks in the Gulf of Alaska would fall 10 to 20 percent in the next 50 years due to climate change. Cheung’s team estimates the drop is more like 20 to 40 percent when you take heatwaves into account.

A dead common murre found in Kodiak during a seven-month beach survey (Photo by Robin Corcoran/USFWS)

Cheung said the compounded impact of heatwaves will affect the entire ecosystem, including marine mammals and seabirds that rely on fish for food. The effects may already be present, he said, in the sweeping seabird die-offs that left almost a million birds starved to death along the West Coast in 2015 during the first “Blob”.

Cheung said there is still a lot of research to be done on the impacts to humans who rely on those fish too.

“We [will] also look at the implications for the dependent human communities, particularly on fisheries that are dependent on these species,” he said. “We are trying to quantify the economics as well as the social impacts associated with … marine heatwave[s].”

The new study models ocean changes on a macro scale. Anne Hollowed, who studies fish stocks for the Alaska Fisheries Science Center said predictions about precisely how and when commercial fish stocks will be impacted is an ongoing field of work.

“How fish move and their availability to coastal communities to harvest them is quite an important issue. To model the very near shore ocean practices requires a finer scale resolution model than the models that William [Cheung] was using,” she said. “You actually need to downscale the global ocean conditions to look at the processes that really govern coastal fish distribution and abundance in areas where coastal communities might be trying to access those fish.”

Hollowed said it’s still too soon to tell how marine heatwaves will impact the future of commercial fisheries, and regulatory agencies are already adopting protocols to use research from Cheung and other scientists to adapt management plans.