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October 24, 2013

Vancouver, B.C. – After spending the summer in his research vessel trying to track resident killer whales with a hydrophone off B.C.’s Central Coast, Vancouver Aquarium cetacean researcher Dr. Lance Barrett-Lennard was struck by the silence. 

“Resident killer whales are typically very vocal in the summer but, for the second year in a row, they have been remarkably quiet,” says Barrett-Lennard, senior marine mammal scientist at the Vancouver Aquarium. “So quiet that we often had difficulty finding them.”

The lack of vocalizations was just one of three “puzzling” changes observed by the Vancouver Aquarium’s cetacean research team. The large, fish-eating mammals were also seen travelling in small groups and travelling further offshore to forage—behaviour that is typically seen in the winter rather than in the summer.

According to Barrett-Lennard, a number of changes within the resident killer whale pods, as well as in their wider environment, may be affecting their behaviour. Over the past two years, the resident killer whales off B.C.’s coast have lost seven matriarchs, the family leaders, which is an unusually high death rate. Normally, the pods only lose one or two matriarchs every couple of years. 

At the same time resident killer whales are exhibiting peculiar behaviour, sightings of Bigg’s (also known as transient) killer whales are on the rise. Over the past 25 years, Barrett-Lennard and colleagues at Fisheries and Oceans Canada noted a substantial increase in sightings of Bigg’s killer whales, which are the mammal eaters. In 1990, resident killer whales were sighted much more frequently than Bigg’s killer whales off the coast of B.C. Today, the numbers are close to equal. 

“It’s unclear at this point if the loss of so many matriarchs or the increase in Bigg’s killer whales is having an impact on resident killer whale behaviour, but the changes we’ve seen over the last two years are striking and beg an explanation, ” adds Barrett-Lennard.


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