Chewed-up orca fins on Russian beach point to cannibalism, and scientists say it may explain why some pods are so tight-knit
The flippers of orcas stranded in the North Pacific are streaked with distinctive tooth marks that suggest the killer whales are sometimes cannibals. Scientists say this could explain why some orcas live in large family groups.
Orcs (Orca Orcinus) come in several distinct types, sometimes considered different subspecies. In the North Pacific Ocean, two of these types inhabit roughly the same areas: resident orcas (Orcinus orca ater) live in large family groups and eat fish, as do Bigg’s orcas (Orcinus orca rectipinnus), which are more common and transient, live in small groups and hunt other mammals, such as whales, dolphins and seals.
In August 2022, co-author of the study Sergei Fominresearcher at the Institute of Pacific Geography in Russia, found an orca fin on a beach on Bering Island, eastern Russia. The fin was bloody and covered in tooth marks.
It is not uncommon to find fins with such tooth marks. But previously, these fins belonged to Baird’s beaked whales (Berardius bairdii) and minke whales (Balaenoptera acutorostrata) who had been attacked and eaten by Bigg’s orcs.
“He immediately thought, ‘Oh, that looks familiar,’ and he thought mammalian killer whales had killed that,” Filatova told Live Science. But that it was an orca flipper was a surprise.
Two years later, in July 2024, he discovered a second dorsal fin from an orca. This one was a little larger, from a young male, but it had the same killer whale teeth marks.
“At that point I started to think it was a trend,” Filatova said. The fins are hard and unfit for eating and prevent a predator from eating the muscle and fat underneath. So the killer whales throw them away, she added.
Genetic testing revealed that the flippers came from southern resident orcas, which reside in waters near Washington state and British Columbia and are known for their carry salmon on your head And give yourself kelp massages.
So it seems that this defense strategy really works
Olga Filatova, whale researcher at the University of Southern Denmark
Filatova and her colleagues believe the southern resident orcas were likely attacked and eaten by Bigg’s orcas.
“At least we know now that cannibalism exists, but I think it’s not very common,” Filatova said.
Researchers suggest that such casual predation by Bigg’s orcas, which prey on mammals, is one reason why resident orcas form large, close-knit family groups. Animals that gather in large groups or herds often do so to protect themselves from predators.
Orcas are generally thought to have no natural predators, but they are known to be aggressive towards each other. In 2016, for example, Bigg orcas were seen hunting and kill a newbornpotentially to force the mother to become sexually receptive. But they didn’t eat the calf.
Teaming up to defend could also help explain sightings of large groups of resident killer whales chasing smaller groups of Bigg orcas, Filatova said. She noted that, in her own work, she has seen Bigg’s orcas avoid groups of resident orcas and return to an area only after the residents have left the area. “So it looks like this defense strategy is really working,” she said.
But not everyone is convinced. “I think the observations of tooth marks on the carcasses of fish-eating whales are interesting and the idea merits further investigation, but there is not yet enough evidence to construct a solid account of the social evolution of fish-eating orcas.” Luke Rendella biologist at the University of St Andrews in Scotland who was not involved in the study, told Live Science by email.
Rendell said the potential benefits of foraging together and passing on specific knowledge about habitat and prey could also be important drivers for creating large groups linked to certain locations.
Other animals have also been suspected of forming close-knit groups to defend themselves against orcas. For example, groups of long-finned pilot whales (Globicephala melas) are also known to confront and hunt killer whales – a behavior that is largely attributed to their highly social nature. And orcas sometimes flee when they hear the calls of pilot whales.
“The similarities between the social structure of short-finned pilot whales and the social structure of resident killer whales, as well as the similarities in how they apparently respond to Bigg’s killer whales, suggest that they may both be responding to potential predation pressure.” Michael Weissresearch director at the Center for Whale Research in Washington, who was not involved in the research, told Live Science by email.
“I certainly think it’s possible that Bigg’s killer whales attacked these two whales,” he said. But he added that scavengers from Bigg’s killer whales or aggression of other resident killer whales while they were still alive, this could also have caused rake marks on the stranded dorsal fins. Therefore, it does not definitively show cannibalism or predation, Weiss said.
Filatova acknowledged that cleaning cannot be ruled out, because Orcas are known to have fed on whale carcasses from whaling.. But she added that fresh killer whale carcasses usually sink quickly, making them inaccessible, and they don’t start floating until a few days later when they begin to decompose. “You have to be really hungry to eat this,” she says.
Filatova also doesn’t think the fin marks are related to fights with other residents, because those marks tend to be on the animals’ sides, she said.
She thinks predator pressure led to the formation of close-knit social groups among resident orcas perhaps 100,000 years ago, after killer whales that evolved separately in the Pacific and the Atlantic began to cross paths; because the social structure proved effective, it remained.
However, she stressed that eating another orca does not appear to be cannibalism for these marine mammals. calls to name them as distinct species. “They never socialize; they never spend time together. To them, it’s just another whale. So why not eat it?” » said Filatova.
Filatova, OA, Fedutin, ID and Fomin, SV (2026). Predation by mammal-feeding Bigg’s killer whales (Orcinus orca rectipinnus) may shape the unique social structure of “resident” piscivorous killer whales (O. o. ater) in the North Pacific. Marine Mammal Science, 42(2). https://doi.org/10.1111/mms.70142
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