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Are Orcas Cannibalizing Each Other? Chewed Up Fins Are Washing Ashore.

Scientists say the grisly finds could point to scavenging, infighting, or something even darker in the ocean food chain.

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Orcas have a reputation for being the ocean’s smartest, meanest overachievers. They hunt in teams, teach their young, and sometimes wear salmon as hats. Then a researcher walks a beach in Russia and finds something that drags the whole mythology into a darker place.

In August 2022, Sergey Fomin, a researcher at Russia’s Pacific Institute of Geography, found a severed orca dorsal fin on Bering Island. It had fresh blood and the familiar rake marks of killer whale teeth. Olga Filatova, a whale researcher at the University of Southern Denmark, told Live Science the bite marks looked like what you see when Bigg’s killer whales attack and eat other marine mammals. The surprise was simple. The fin belonged to an orca.

Two years later, in July 2024, Fomin found another orca fin about two kilometers from the first. Same story. Same tooth marks. Filatova said, “At that moment, I started thinking that this is a pattern.” The fins themselves don’t offer much payoff to a predator. They’re tough, not exactly a snack, and they get in the way of reaching the muscle and blubber underneath. So the attacker must tear them off and leave them.

Orca Fins With Tooth Marks Wash Up in Russia, Raising Cannibalism Questions

Genetic testing linked both fins to southern resident killer whales, the fish-eating orcas of the Pacific Northwest that live in large, long-running family groups. Filatova and her co-authors published their analysis in Marine Mammal Science on Feb. 24. Their best guess points to Bigg’s killer whales, the mammal-hunting type that travels in smaller groups, as the likely attackers.

Filatova didn’t oversell it: “At least now we know that cannibalism happens, but I think it is not super common.”

Here’s where it gets interesting, and a little grim. Resident orcas stick together in unusually large family groups. That social structure looks sweet when we talk about it in human terms. It also works as protection. Bigg’s orcas may think twice about rushing a crowd. Filatova has seen Bigg’s orcas avoid resident groups and come back after the residents leave. “So, it looks like this defense strategy is really working,” she said.

Not everyone wants to build a grand evolutionary story off two fins. Luke Rendell, a biologist at the University of St Andrews who was not involved in the research, told Live Science there isn’t enough evidence yet to explain the entire social evolution of fish-eating orcas. Michael Weiss at the Center for Whale Research also raised other possibilities, including scavenging.

Filatova doesn’t love the scavenging theory because fresh killer whale carcasses sink quickly and only float later, once decomposition starts. “You need to be really hungry to eat this,” she said.

Then she raised the question that hangs over the whole thing. If these groups never mix, is “cannibalism” even the right word?  “They never socialize; they never spend time together. For them, it’s just another whale. So why not eat it?”

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