International fleet studying North Pacific salmon populations

The largest-ever ecosystem survey of salmon across the North Pacific Ocean is bringing together 60 scientists from five nations and a flotilla of four research vessels to learn more about increasingly extreme climate variability and its effects on salmon survival.

The USD 10 million (EUR 8.8 million) research effort was organized through the International Year of the Salmon, a project support by the North Pacific Anadromous Fish Commission, a treaty organization including the U.S., Canada, Russia, Japan, and South Korea that was originally created to control high-seas driftnetting for salmon. The 2022 Pan-Pacific Winter High Seas Expedition will engage in detailed sampling, using the four research vessels to scan areas 60 nautical miles apart on the high seas. Researchers hope the sea sweep can offer some explanation for fluctuations in salmon populations in reaction to big swings in ocean temperatures, and better predict the future of key salmon spawning populations affected by climate change.

A NOAA research vessel, the Bell M. Shimada, will take the lead departing from Port Angeles, Washington, U.S.A. on Tuesday, 1 February to start its survey track between the 47th parallel south of Seattle north to Kodiak Island, followed by Canadian and Russian vessels setting out to cover other salmon survey areas – as far as 800 miles offshore.

Salmon spend most of their life – five to six years – in the ocean before swimming to freshwater rivers for spawning, according to Laurie Weitkamp, a research fisheries biologist at the NMFS Northwest Fisheries Science Center who is leading the first leg of the Shimada’s research cruise.

“It’s also the one [life phase] we know the least about,” Weitkamp said. “When they go out in the ocean, they enter a kind of black box.”

After young salmon make their way to the ocean at summer’s end, winter is the second critical period of their lives, as they are beset by predators and striving for food. Weitkamp said the most-recent survey, completed in 2019, portended a tough future for chum salmon.

“We saw a lot of really, really skinny chum salmon. It looked like they were starving to death,” she said.

Years of wide fluctuations in ocean temperature have had uneven effects on salmon stocks, according to Ed Farley, a biologist with the NMFS Alaska Fisheries Science Center in Juneau. In the 2021 season there was a collapse of chum salmon returns to the Yukon River, but Bristol Bay sockeye returns were at record highs. Those fish spend their sea years in different regions: Yukon River chum are found in the Gulf of Alaska, while Bristol Bay sockeye are found south of the Aleutians and farther west, Farley said.

“That’s why these surveys in the winter are so important,” he said.

The biggest threat to salmon populations worldwide is climate change, biologists say.

The 2015 warm-water “blob” and ocean heat waves that disrupted the North Pacific fisheries are suspected to be the triggers for fluctuations in salmon spawning returns. The four research vessels involved in the project will collect data on ocean conditions, and studying the food web by making one-hour sampling trawl tows at 155 stations about 60 nautical miles apart from the U.S. Northwest out to the end of the Aleutian Islands chain.

Scientists on board will gather genetic samples from captured fish, hoping to link those found at sea to fish that swim in the spawning rivers. An autonomous undersea glider vehicle, controlled from the University of Alaska at Fairbanks, will shadow the Shimada’s route, diving down past 600 feet to record and transmit back oceanographic data.

“This is probably the boldest, most far-reaching survey of the open ocean in the North Pacific ocean that’s ever taken place,” Mark Saunders, an expedition organizer with the International Year of the Salmon, said during a 28 January conference call with news reporters.

“[With] climate change we’re seeing now, the impacts are severe,” Saunders said. “’The timing is really now to begin to understand this.”

The research vessels will pull samples to measure environmental and ecosystem influences ranging from plankton to large predators like salmon sharks. A Canadian commercial vessel will use gillnets to assess how effective bigger trawl nets are in accurately gauging fish populations, specifically in regard to the composition of salmon and steelhead in surface waters. Genetic sampling will use to link fish found at sea to spawning populations in rivers around the North Pacific.

“If we can understand where these fish are in the open ocean, we can begin to link it to understanding management systems and actions in freshwater that will need to know what the potential fate for these animals is under a changing climate system,” said Saunders.

And analysis on genetic samples that scientists collect at sea will be key to linking salmon caught at sea to the rivers where they spawn, according to Weitkamp.

“We can take a little fin clip and know exactly where it came from,” Weitkamp said.

In all, the effort involves 10 government agencies and the British Columbia Salmon Restoration and Innovation Fund. The research vessels’ tracks and reports, as well as photos, videos, and notes from the expedition’s researchers, will be posted publicly on the International Year of the Salmon website. The last of the expedition’s cruises will end in April 2022, and final reports will be posted in May, with preliminary findings released at a symposium in Vancouver, Canada in October 2022.

Reporting by Kirk Moore

Photo courtesy of NOAA