Post-mortem shows pilot whales were healthy before they swam ashore and died in N.S.

HALIFAX -

Animal autopsies on several pilot whales that washed ashore last weekend in Cape Breton indicate the whales were healthy, says a marine animal conservation group.

Tonya Wimmer, executive director of the Marine Animal Response Society, says necropsies performed on eight of the whales suggest the animals were not following a sick member who had become disoriented and led them to shore.

While the final necropsy results aren't in yet, Wimmer says the whales potentially swam to their deaths because they weren't paying attention to where they were going. Whales, she says, are often following food and don't realize the ocean water receding as they approach the shore.

"They don't seem to realize the tide is actually dropping underneath them, and they do get stuck," she said in a recent interview.

In total, 11 whales came ashore Sunday in Port Hood, N.S., but three were pushed back into the water by passersby and survived.

The whales were a mix of males and females, Wimmer said, with the largest around five metres long. "They're not as big as their cousin, the killer whale," she said, "but they can get quite big."

They were a part of a larger group of about 30 pilot whales swimming nearby, she said, which included "extremely small" calves.

The remaining whales were carefully herded by boats back out into the ocean, Wimmer said, to ensure the larger group wouldn't also swim ashore. She noted there are only a few channels to "sneak" into the shallow, enclosed bay where the eight ultimately died.

"It's very surprising that these highly intelligent, very social animals at times make these mistakes and end up running aground," she said, adding that it's not uncommon behaviour for the species globally.

Elizabeth Zwamborn, a PhD candidate at Dalhousie University's Whitehead Lab who has been studying pilot whales since 2013, says this particular breed is "notorious" for mass-stranding events, sometimes swimming ashore and dying after being spooked by loud noises such as underwater explosions.

 Pilot whales are social creatures, Zwamborn said, with sons and daughters staying with their mothers for life, living in "very tight-knit groups." Their echolocation skills can be compromised in shallow waters with twisty channels, she added.

"That seems to be a commonality in many of the strandings," she said. "Not all, but many. They simply can't find their way out and they panic, and end up on the beach."

Zwamborn said wildlife pathologists would review the information from the necropsies to better understand how the animals died. Sometimes, she added, the reason can't be determined, but "it's just as important to find out what it wasn't, as it is to find out what the cause is."

This report by The Canadian Press was first published June 14, 2023.

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