Animal Advocates Watchdog
Researchers debate why fish-eating killer whales are snuffing porpoises
By Larry Pynn, Vancouver Sun October 9, 2009 Be the first to post a comment
Natural born killers or misunderstood mamas?
Scientists are grasping for answers to explain why southern resident killer whales — a group of fish eaters that prefer chinook salmon — have also been observed toying with harbour porpoises before leaving them dead, including two cases in the past month in Washington state and B.C.’s Strait of Georgia.
Joe Gaydos, staff scientist with the SeaDoc Society, speculated in an interview Tuesday that killer whales might see the porpoises as an opportunity for a playful “cat and mouse” game — albeit with deadly consequences.
“The thing we forget about wildlife is that they don’t really have a consciousness like we have, that this is okay and this is not okay,” he said from his office in Washington’s San Juan Islands.
“Cats don’t think, ‘oh, it’s not okay to play with it [a mouse].’ They just do it. That’s what an animal does.”
But John Ford, a whale expert with the federal fisheries department, said from Nanaimo that because it is female killer whales that tend to engage in the behaviour, it is possible they are trying to prop up the porpoises as they might their own young. The porpoises can ultimately succumb to shock, exhaustion, injury or drowning.
“It could be a maternal-driven behaviour that is misdirected towards another species,” said Ford, noting southern residents seem more likely to exhibit the behaviour than northern resident killer whales.
“These animals [porpoises] are often sort of carried about on their backs or heads, pushed around. It’s almost like a behaviour you’d see with a distressed or dead calf of a killer whale. We’ve seen a still-born calf pushed along or carried along by the mother.”
Ford said biologists observe killer whales kill porpoises locally about twice a year, but confirms what they see must be only a portion of the total number of porpoises killed this way.
Lance Barrett-Lennard, a whale biologist with the Vancouver Aquarium, said he’s observed two northern resident females trap a harbour porpoise between them in the water, and ultimately let it swim away.
But he said the southern residents seem to be “more aggressive” with harbour porpoises, adding it’s possible that one or two whales started the “sport” and it became a “learned behaviour” in the pods.
A 2005 paper co-authored by Gaydos reported the discovery of 13 dead harbour seal pups in the San Juan Islands. It found evidence of a “novel pattern of killing without intent to eat” by “one or more transient killer whales” — a separate group that targets marine mammals and not fish — although resident killer whales could not be completely exonerated in connection with the seal deaths.
J-pod killer whale (J-31) throwing harbor porpoise in air.
Photograph by: Robin W. Baird, cascadiaresearch.org
