Biology

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

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Two marine mammal scientists from the University of British Columbia have discovered that the claim that a lack of access to salmon is the cause of the plummeting population of killer whales in the southern Pacific Ocean is false.

In a paper published on the open access site PLOS ONE, Burak Saigiri and Andrew Treitz discuss how they consulted with sport anglers and whale watching crews to learn more about access to Chinook salmon by killer whales. It explains what happened.

Previous studies have shown that killer whales in the southern Pacific Ocean are struggling. Not only are their numbers decreasing, but the number of offspring is also decreasing dramatically. And no one knows why.

The southern Pacific killer whales are a group of killer whales that live in parts of the Salish Sea off the coast of North America from California to British Columbia. According to the latest census, there are only 73 individuals left, living in three herds. Whales swim north during the warmer months and then head south again when winter arrives.

But no matter how you look at it, they are struggling to survive. What makes their struggle even more bizarre is that they are the only marine mammals in their ecosystem that are struggling. Harbor seals thrive, as do other species of whales, porpoises, and sea lions.

Some in the sector suggest the problem is the lack of access to salmon, the whales’ main food source. But sport fishermen who target salmon report having no trouble catching them, and residents in the south have been seen doing the same. Whale-watching crews also told researchers they regularly see endangered killer whales swimming among schools of salmon.

Researchers suggest this indicates that the whales are having a hard time catching them. And they further suggest that it may be due to the noise the boat makes. They note that the area they live in has far more maritime traffic than areas further north, where northern resident killer whales thrive.

They also suggest that whales may be unable to feed at different times of the year. For example, you may be able to catch enough salmon during the summer, but not in the spring. This scenario would explain why one puppy was found starved to death this spring.

Further information: Burak Saygili et al. Chinook salmon prevalence is higher in southern than northern killer whales at summer hotspot feeding grounds, PLOS ONE (2024). DOI: 10.1371/journal.pone.0311388

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Source: Scientists discover Pacific southern killer whales have access to ample food, deepening mystery of their struggle (October 20, 2024) https://phys.org/news/2024-10-scientists Retrieved October 20, 2024 from -southern- killer whale-pacific.html

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