Are whales killing porpoises on purpose?

Natural-born killers or misunderstood mamas?

Scientists are grasping for answers to explain why southern resident killer whales--a group of fish eaters that prefers 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 that killer whales might see the porpoises as an opportunity for a playful "cat and mouse" game--with deadly consequences.

"The thing we forget about wildlife is that they don't really have a consciousness like we have, that this is OK and this is not OK," he said from his office in Washington's San Juan Islands.

"Cats don't think, 'Oh, it's not OK 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, B. C., that because female killer whales 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 stillborn calf pushed along or carried along by the mother."

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.