Christopher Dunagan

Puget Sound Institute

After five weeks at sea, a team of 21 scientists from five countries returned Monday with some surprising findings about the mysterious lives of salmon in the Pacific Ocean, according to Laurie Weitkamp, a salmon biologist with NOAA’s Northwest Fisheries Science Center in Newport, Oregon.

“It was quite an experience,” said Weitkamp, one of three chief scientists aboard the Russian research vessel Professor Kaganovsky.

The expedition was part of activities associated with the International Year of the Salmon and was meant to look at how salmon fare in the open ocean. Among the surprises that emerged from the cruise was the relatively small number of pink salmon. Pinks, the most abundant salmon in the Pacific Ocean, normally make up about half of all the salmon in the region. Yet during the expedition — which covered some 345,000 square miles — pink salmon made up only about 10 percent of the salmon caught in the researchers’ nets.

“We kept asking, ‘Where are the pinks? Why aren’t you here?’” Weitkamp recalled.

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Russian members of the crew spent about two weeks collecting fish in the Western Pacific Ocean before crossing over to North America and picking up the remainder of the research team in Vancouver, British Columbia.

“They weren’t finding many pink salmon there either,” she said.

Some speculated that the pinks had moved from the deep ocean into coastal waters during the February-March time period. Another possibility is that some pinks had moved south. It appeared that more pink salmon were caught by the researchers in the southern portion of the study area, which stretched south to a line extending west from Seattle.

The most abundant salmon caught in the research nets was chum, Weitkamp said. They were distributed throughout the study area, perhaps with slightly more toward the south.

“Chum were really interesting,” she said. “Previous research has shown that most of them are probably Asian,” arriving from across the ocean.

Many of the chum were skinny, as if they hadn’t gotten enough food, and their stomachs were empty. Younger chum seemed to be in somewhat better condition.

On the other hand, coho salmon were in far better shape. They were the second-most-abundant fish caught in the study, which was another big surprise. Other studies, conducted mostly in the summer, had led researchers to believe that coho stayed in the coastal regions. That seemed reasonable, since coho spend only a year-and-a-half in the ocean. And yet here they were far out at sea.

“The coho looked great,” Weitkamp said. “They had full stomachs. But it’s really puzzling, because we thought that they were a coastal fish.”

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Why coho were foraging well and chum were practically starving has not yet been explained, Weitkamp said. Was it a preference for a particular food, or did one of the species arrive within the study area after spending time where prey availability was different?

Sockeye salmon provided another interesting finding, Weitkamp said. Water temperatures seemed to be satisfactory for sockeye throughout the study area, yet sockeye seemed to congregate more in the northern portion, including areas as far north as Kodiak, Alaska.

Only three Chinook salmon were caught during the entire trip, according to Weitkamp, probably because they were staying in water too deep to be caught using nets that stretched down to 160 feet.

Genetic testing of salmon tissues at sea showed a mixture of species coming from streams as far north as Alaska and as far south as the Columbia River. Further testing following the expedition could determine the origins of all the fish caught, providing evidence of where salmon may go during the winter months at sea.

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“One thing we don’t know is whether what we saw was typical,” Weitkamp said, noting that this is just one year and the researchers are fully aware that conditions can change and fish can move around.

To clarify, she said, imagine Times Square in New York City on New Year’s Eve. One can’t assume that the huge crowds one sees at that time will be there all year round. Further studies are needed to establish the most typical patterns for salmon, as the search for explanations goes on.

What the fish were eating, as found by examining their stomach contents, was fairly consistent with what was being caught in the various nets designed to catch plankton and smaller fish, Weitkamp said. Krill, especially in the northern areas, was a common prey for the salmon, while 3- to 4-inch lanternfish — which rise to the surface only at night — were common throughout the area.

The nets caught a lot of squid, she said, but the species of squid eaten by Chinook as well as some of the coho and sockeye are a species that lives in water too deep for the nets to reach. Why the salmon chose the deep-water squid and not the shallow-water variety that seemed abundant in the area remains another unanswered question.

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Many of the scientists returned home with samples of marine life to be examined and shared with many more colleagues unable to be accommodated on the vessel. Some will be examining salmon tissues genetically to determine where the fish came from.

Others will take a close look at the ear bones, or otoliths, to measure growth rates and compare them with fish leaving and returning to the streams. It has long been suspected that faster-growing salmon are better suited to avoid predators and survive through winters of low prey abundance.

Still others will measure the ratio of various chemicals found in the fish tissues to determine where in the ocean the fish had likely gained the most weight.

Measuring the density of prey found during the expedition and combining that with other information about the Eastern Pacific could help determine the region’s carrying capacity — a measure of how many fish and other creatures can survive within the prescribed area.

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Organizers and researchers would like to conduct a follow-up expedition to determine if this year’s findings will hold up to further scrutiny and to investigate the possible reasons for all the unexpected findings.

The expedition was conceived by longtime Canadian salmon researcher Dick Beamish, who helped raise $1 million for the five-week voyage involving the Russian crew, which was experienced in winter fishing and taking scientific measurements under grueling high-seas conditions.

This article was written for the Puget Sound Institute. PSI, which is affiliated with the University of Washington, publishes the Encyclopedia of Puget Sound. To read more, click here.