Killer whales carrying dead salmon leave scientists baffled

Killer whales off the coast of Washington state have been carrying salmon carcasses on their heads for decades, but researchers still don't know why they do it.

Killer whales in the Pacific Northwest have begun wearing salmon hats again, reviving a bizarre habit first described in the 1980s. Last month, scientists and whale watchers saw killer whales ( Orcinus orca ) in the South Puget Sound and off Point No Point in Washington state swimming with salmon carcasses on their heads, Live Science reported on November 27.

Killer whales have resumed the trend of carrying salmon carcasses on their heads. (Photo: Tory Kallman).

It was the first time they had donned the unusual accessory since the summer of 1987, when a female killer whale off the West Coast began the behavior for unknown reasons. Within two weeks, the rest of the pod followed suit, turning salmon carcasses into matching fashion accessories, according to the marine conservation charity ORCA, but researchers are unclear whether the same thing will happen this time.

Researchers believe that killer whales wearing salmon hats may have joined the trend when it first emerged nearly 40 years ago. 'It's possible that some individuals who did it the first time have done it again,' said Andrew Foote, an evolutionary ecologist at the University of Oslo in Norway.

The motivation behind the salmon hat trend remains a mystery , according to Deborah Giles, a killer whale researcher at the University of Washington. Salmon hats are a perfect example of a 'fad,' a behavior that starts in one or two individuals and is adopted temporarily by other members of the group before fading away. In the 1980s, the trend lasted only a year. By the summer of 1988, salmon hats had disappeared from the West Coast killer whale population.

Researchers speculate that salmon hat-wearing behavior may be related to food availability. The South Puget Sound is currently teeming with pike salmon (Oncorhynchus keta) . With so much food to eat at one time, killer whales may be saving fish to eat later by balancing them on their heads.

Killer whales have also been observed storing food elsewhere. Giles and his colleagues have seen killer whales carrying large pieces of food under their pectoral fins, held tightly to the sides of their bodies. Salmon may be too small to hold under their pectoral fins, so they choose to carry them on their heads instead.

Drones equipped with cameras could help researchers track killer whales wearing salmon helmets in a way that was more feasible than 37 years ago. Over time, Giles's team could collect enough information to reveal how long an individual carried a fish carcass before eating it. But the food availability hypothesis could be wrong if the footage revealed that the killer whales skipped out on eating salmon.