Monday, November 29, 2021
Nov. 29, 2021

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Researchers make surprising discovery while tracking Chinook salmon in Salish Sea, B.C.

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SEATTLE —Researchers made a surprising discovery while tracking Chinook salmon in both the foraging areas of endangered southern resident orcas and the growing, healthy population of the northern resident orcas in B.C.

In a study published last week in the Canadian Journal of Fisheries and Aquatic Sciences, the researchers stated they expected to find the robust population of northern residents fat with fish, and the southern residents stuck with lean pickings.

Instead, the team found four to six times the density of big Chinook in the area they tested in the Strait of Juan de Fuca, part of the southern residents’ core foraging area, compared with the area they sampled in the northern residents’ territory, in the Johnstone Strait.

“It was the opposite of what we expected,” said Andrew Trites, an author on the paper and director of the marine mammal research unit at the University of British Columbia.

The team used acoustic detectors and dropped fishing nets and lines in the water to assess Chinook density in the select areas during the summers of 2018 and 2019.

Trites said the study findings challenge the hypothesis that southern resident orcas can’t get enough Chinook to eat in the Salish Sea during the summer, and mean that researchers need to investigate whether a combination of other factors is affecting foraging success.

The new findings have drawn criticism among other scientists in the field and sparked a critique Thursday from a dozen orca researchers and nonprofits.

Those researchers and others uninvolved in the study say the data is far too thin and the sampling area too small — and not even correct — to support such a sweeping conclusion.

“They are making a lot of assumptions and my concern is that once you stitch all those assumptions together, you can end up with an answer that is incorrect,” said Brad Hanson of the National Oceanic and Atmospheric Administration’s Northwest Fisheries Science Center in Seattle.

One such assumption is concluding that just because fish are seen in one place, the whales can or do eat them in that area at that time.

He also cautioned the findings could be “weaponized” to say more than the researchers did. “It will be used by those who want to say, ‘See, we told you fish aren’t a problem,’” he said.

Trites stressed the findings do not mean the orcas are not nutritionally stressed: “We are not saying they are not food-limited because by body condition they are malnourished compared with the northern residents.”

Nor do the findings show Chinook are not in decline — most populations are, throughout the southern residents’ foraging range.

But the findings do show, Trites said, that the whales are not food-limited in the area and during the season in which they tested.

“Imagine the first scientist who said the earth wasn’t flat,” said Trites, summing up how surprising and counter to expectation the findings are.

Study’s support, critiques

The orcas were listed as endangered in 2005 and are not recovering; there are only 73 left. In addition to lack of adequate prey, particularly Chinook, noise and disturbance by vessels and boats that limits the orcas’ ability to hunt, as well as pollution, have been identified by scientists as three main threats to the survival of the J, K and L pods of orcas that frequent Puget Sound.

Eric Ward, a statistician at NOAA’s Northwest Fisheries Science Center whose work is used to model salmon populations, said the paper sheds new light on inconsistencies with the orcas-are-hungry hypothesis.

“This seems to be an important paper that may help reduce our uncertainties in factors limiting killer whale recovery,” Ward said in an email. “I think this is consistent with views that prey limitation is probably not the most important factor preventing SRKW recovery. There’s a number of other data points that point in the same direction.”

For one, Ward said, a large cohort of K-pod females went through their reproductive prime years during a time when Chinook abundance was better in the Columbia River, but they still mostly did not produce any offspring.

But others said the paper is just a start and allows only limited conclusions in part because the researchers didn’t look where most orcas are feeding.

Research published in June by Fisheries and Oceans Canada based on southern resident sightings, and other sources from 2009 to 2020, shows the southern residents forage in areas other than where the research team tested. Most notably missed was Swiftsure Bank, west of the study area.

The area of Johnstone Strait sampled also has dropped off as a core foraging area by most northern residents in recent years, said John Durban of Southall Environmental Associates. “It doesn’t seem there are enough food there in recent years to support the majority northern resident killer whale population, and it is a shame the prey surveys didn’t cover the full population’s range where most of the whales feed.”own research has documented both an improvement lately in southern residents, especially J pod, that which correlates with better fish populations in parts of the Strait of Juan de Fuca, as well as decline in body condition of northern residents that use the area that the team sampled in Johnstone Strait, said Fearnbach of SR3.

To Durban and Holly Fearnbach of SR3, who survey the orcas’ body condition using drone photography, the paper does not debunk the link between body condition and prey, but actually confirmed what is far from new.

“Our colleague John Ford more than a decade ago found that both populations experienced simultaneous periods of high mortality when Chinook salmon returns were relatively low, particularly in the 1990s,” Durban said.

Hanson, of NOAA, praised the researchers for taking on a tough problem in ways no one had tried before — but said the findings need to be replicated before they could inform any new direction for understanding what is limiting orca recovery.

The paper is “just one more idea” that needs to be tested in an attempt to replicate the results before they can be relied on, Hanson said. “The point is you can have all sorts of fish in an area but if the whales aren’t using it, what they are experiencing might be quite different from the area you are surveying.”

He was a reviewer on the paper and called out his concerns with the sampling design.

Ken Balcomb, founding director of the Center for Whale Research, dismissed the paper as “a nice little fish thing” that proved nothing as to the amount of fish available for the southern residents throughout their range and year.

Deborah Giles, research director for the nonprofit Wild Orca and biologist for the University of Washington’s Center for Conservation Biology, said the findings go against 40 years of data on the southern residents and their prey.

“To say the southern residents are getting four to six times as much salmon as the northern residents is just silly,” Giles said. “And here we are, trying to find a nice way to say that.”

Efforts to boost salmon

Orcas are not adapted to fasting and must eat every day to be in top condition and nurture their families.

Scientists have for years raised the problem that an abundance of fish in one area does not a well-fed southern resident orca make. Rather, the southern residents face the problem of serial failures, in which in one river after another throughout their seasonal foraging round, they can’t regularly get enough to eat.

In response, NOAA and other agencies have invested heavily in boosting prey to rebuild the southern resident population.

NOAA also has just approved ocean fishing cutbacks to leave more food for orcas when Chinook levels fall below trigger points.

Uncounted millions of dollars also are being spent on salmon habitat restoration in Puget Sound and beyond in part to provide more prey to help orcas recover. Canada also has implemented fishing cutbacks on Chinook to leave more fish for the southern residents, and so has the state of Washington.

Hatcheries, too, are pumping out more salmon to feed orcas in what amounts to what may be the world’s largest-ever wild animal feeding effort.

Federal, state and tribal salmon hatcheries in Washington and Oregon produced more than 11.6 million additional juvenile hatchery Chinook salmon in 2020 compared to previous years. And they released more than 18.3 million additional Chinook salmon in 2021.

All of it intended to be orca chow.

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