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Endangered southern resident killer whales (SRKW) have returned to the Salish Sea after a prolonged absence, but researchers say drastic action is needed to replenish the whales’ food source and keep them returning to their core habitat.

Until recently, the fish-eating SRKW clan had not been seen in the waters of southern B.C. and northern Washington State since early May, because the depletion of their food source has forced them to look elsewhere.

But last week, researchers with Fisheries and Oceans Canada (DFO) encountered whales on the west coast of Vancouver Island from all three groups – referred to as the J, K and L pods – that make up the SRKW population. The researchers also saw a new calf swimming with its mother, known as J31.

On Friday, U.S. researchers also spotted every member of the J and K pods – and possibly some from the L pod – off the west side of San Juan Island.

“There’s lots of tail flapping and breaching and kelping, where they kind of swim through the kelp with the seaweed draped over their fins,” said Monika Wieland Shields, president of the Orca Behavior Institute on San Juan Island, Wash.

“They’re now doing what we call the west-side shuffle, going north and south on the west side of San Juan Island,” she said. “They’ve probably gone back and forth four or five times today already.“

The SRKW population has fluctuated between 70 and 99 members since 1976, according to the DFO. There are currently 76 members, including the calf born this spring.

The known range of the SRKW clan extends from southeastern Alaska to central California, but the whales typically concentrate in the area around southern B.C. and northern Washington State during the summer months.

Ms. Wieland Shields said that 10 or 15 years ago, it was common to see the whales on a near-daily basis in local waters during the warmer months.

“When they’re in the Salish Sea in the spring and summer, they’re relying heavily on the salmon near the Fraser River – and the spring salmon runs have just crashed since 2005,” Ms. Wieland Shields said.

“The fact that they’re not here is definitely telling us that there has been a major ecosystem shift.”

Other factors compound the threat to southern residents. Researchers are concerned, for example, about toxic contaminants in the water, which the whales acquire through their food and store in their blubber.

“When they’re not getting enough to eat, they metabolize those toxins and it affects their immune system and fertility, so they’re more susceptible to disease and less likely to have successful pregnancies,” Ms. Wieland Shields said.

Underwater ocean noise, such as that coming from shipping and tanker traffic, can also impede the whales’ echolocation, making it harder to locate food sources that are present.

In contrast, transient killer whales that prey on mammals such as harbour seals have enough food and are less affected by the same toxins and noise.

Chinook salmon populations have been in decline for years as a result of factors including habitat destruction, harvest and the effects of climate change, according to the DFO. Of 13 wild Fraser River Chinook salmon populations assessed by the department, only one is not at risk.

In April, Ottawa announced new measures aimed at addressing the Fraser River Chinook decline. This included closing commercial troll fisheries for Chinook until Aug. 20, after migrating populations have passed through, and imposing stricter limits and windows for recreational fishing.

Ms. Wieland Shields described the Salish Sea as an area of not only biological importance for the southern resident population but also cultural importance, as it is where all the pods traditionally come together for greeting ceremonies and to form superpods.

“If we want them to come back to the Salish Sea, then we need to focus on restoring salmon on the Fraser River, which will involve addressing fish farms, contamination and run-off and the faulty floodgates at the mouth of the river,” she said.

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