Scientists discover southern Pacific killer whales have access to enough food, deepening mystery of their struggles

Two marine mammal scientists from the University of British Columbia have found that claims that lack of access to salmon is behind the collapse of the southern Pacific resident killer whale population are false.

In their article published on the open access site PLOS ONEBurak Saygili and Andrew Trites describe how they consulted with sport fishermen and whale watching teams to learn more about orcas’ access to Chinook salmon.

Previous research has shown that southern Pacific resident killer whales are in trouble. Not only are their numbers decreasing, but the number of their descendants is decreasing significantly. And no one knows why.

Southern Pacific Resident Killer Whales are a group of orcas that live off the coast of North America, from California to British Columbia, in parts of the Salish Sea. The latest census showed that there are only 73 left, living in three groups. Whales swim north during the warmer months, then head south again when winter arrives.

But clearly they are struggling to survive. What makes their struggles all the stranger is that they are the only struggling marine mammal in their ecosystem: Harbor seals thrive, as do other types of whales, porpoises, and sea lions.

Some in the field have suggested the problem is lack of access to salmon, the whales’ main food source. But sport fishermen looking for salmon report no problems catching them and have seen southern residents doing the same. And whale-watching teams told researchers they regularly see endangered orcas swimming among pods of salmon.

According to the researchers, this indicates that the whales are having difficulty catching them. And this, they further suggest, could be due to the noise made by the boats. They note that the area they live in sees much more maritime traffic than areas further north where the northern resident orcas thrive.

They suggest it is also possible that whales have difficulty eating at different times of the year; they may find enough salmon during the summer, for example, but have difficulty in the spring, a scenario that would explain why a calf died of starvation last spring.

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