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Hungry killer whales focus on feeding

Aug 21 2012

Food, rather than sex and parties, appears to be topof-mind for threatened northern resident killer whales this summer.

Lance Barrett-Lennard, senior marine mammal scientist for the Vancouver Aquarium, said northern residents are displaying behaviour more often seen in winter, including travelling in small groups rather than the superpods they typically form at this time of year.

"We are finding small groups that tend to be pretty focused on feeding and, acoustically, they are fairly quiet, which is a bit puzzling for us," said Barrett-Lennard, who has led three cetacean research trips over the summer.

It's a poor year for chinook salmon - resident killer whales' preferred food - and the whales seem to be putting all their energy into hunting, he said.

"I think what is going on is the whales are working hard at making a living," said Barrett-Lennard, who suspects the whales remain quieter when they are feeding intently because they don't want to attract a lot of other whales. "Or maybe they're not feeling social," he said.

Superpods, when most of the approximately 250 members of the northern resident community come together, are times of intense socialization when most of the mating occurs.

However, Barrett-Lennard expects the whales will eventually find time to mate. Previous research has shown that, in poor food years, mortality has increased, but the birth rate has remained steady.

"It's not good news, but I wouldn't describe it as a crisis yet," he said.

"We will certainly keep our eyes on the population to see what happens over the next few months."

The situation could improve if there are strong chum salmon runs, as the whales will eat chum when there are no chinook, he said.

During research cruises, which took the Vancouver Aquarium crew into the Central Coast, Rivers Inlet and Queen Charlotte Sound areas, there was also a rare encounter with a group of offshore killer whales.

Little is known about the estimated 250 to 300 offshore whales, which travel from the south Bering Sea to Mexico.

It was unusual to see a group of 50 to 60 in relatively shallow water, Barrett-Lennard said.

Their diet consists largely of sharks, but that day, they were more interested in social activity and playing in the kelp, he said.

"And they were talking their heads off. We heard them through the hull of the boat before we dropped the hydrophones."

Unusual behaviour was also seen among Pacific white-sided dolphins, which were hanging around the outer coast instead of their usual territory in deep, mainland fjords, Barrett-Lennard said.

"They were swimming with resident killer whales and humpback in the same way they ride alongside boats," he said.

"They are thrill seekers. That's what white-sided dolphins are all about. They were having a lot of fun riding along with the whales, but it seems to be risky behaviour. If they made a mistake and swam alongside a transient, it would be really bad."

Transient killer whales eat marine mammals, not fish.