Orca population in Puget Sound falling

Not only are Puget Sound’s resident killer whales continuing to decline in numbers, but their behavior is changing, too, according to scientists. The orcas seem to be splintering from their basic social groups and spending less time together.

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FRIDAY HARBOR — With two new deaths this year and no new calves since 2012, the population of endangered killer whales in the Puget Sound continues to decline.

The number of whales in the J, K and L pods has dropped to 78, a level not seen since 1985, according to a census by the Center for Whale Research. Adding to the concerns, the whales appear to be “splintering” from their pods, which are their basic social groups.

Since 1976, Ken Balcomb of the research center has been observing the Puget Sound orcas, or Southern Residents as they’re known among scientists. Balcomb compiles an annual census of the population for submission to the federal government.

Historically, all three pods of orcas have come together in the San Juan Islands during summer months, often feeding and socializing in large groups, Balcomb noted. But for the past few years, the pods have divided themselves into small groups, sometimes staying together but often staying apart.

“What we’re seeing with this weird association pattern is two or three members of one pod with two or three from another pod,” Balcomb said. “It’s a fragmentation of the formal social structure, and you can see that fragmentation going further. They are often staying miles and miles apart and not interacting.

“If we were trying to name the pods now, we couldn’t do it,” he added. “They aren’t associating in those patterns anymore.”

Among killer whales, offspring tend to stay with their mothers for life, sustaining identifiable “matrilines” that typically contain youngsters, their mothers and their grandmothers. So far, the matrilines have stayed together, though many of these groups are now smaller.

Balcomb suggests the primary factor for the population decline is a lack of food for the killer whales, which generally prey on chinook salmon passing through the San Juan Islands on the way back to Canada’s Fraser River. The whales have a strong preference for chinook, typically larger and fatter fish, but they will eat other species of salmon and even other fish sometimes.

Read the full article: http://seattletimes.com/html/localnews/2024429124_orcadeclinexml.html

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