Severed Fin Reveals Rare Killer Whale Cannibalism and Questions the Differences in Orca Species

Some killer whales do not get along with others and, in extreme cases, can cannibalize members of their own species. The notion of cannibalistic killer whales, however, is more complicated than it seems at first glance. The stark differences between different groups of killer whales have led researchers to question whether there really is a single species of killer whale or multiple subspecies.

A new study published in Marine Mammal Science was confronted with the question of killer whale cannibalism at a maritime crime scene on Bering Island, off Russia’s Pacific coast, where severed killer whale flippers marked with the teeth of another whale were discovered twice in 2022 and 2024.

This evidence provides insight into two groups of killer whales that differ in many ways, from their diets to their social structures.

“They certainly do not perceive themselves as belonging to the same species. For transient groups, resident killer whales are simply prey,” study author Olga Filatova, a whale researcher and associate professor at the University of Southern Denmark, said in a statement.

Questioning killer whale cannibalism

Although there is technically only one species of killer whale… Orca Orcinus — several groups of whales display their own specialized behaviors. These groups are recognized as ecotypes, populations of a species that exhibit distinct characteristics in response to ecological conditions; these characteristics are generally considered too subtle to justify classification of an ecotype into a new subspecies.

In the North Pacific, there are three recognized ecotypes of killer whales: resident, transient, and offshore. Each ecotype leads a different life, as evidenced by the contrast between residents and travelers. While residents feed primarily on fish and live in large, close-knit families, transients (also called Bigg’s killer whales) hunt marine mammals and travel in smaller, looser social units, often leaving their families at a young age.

When the whales’ torn fins were found on Bering Island, researchers suspected that one killer whale had probably eaten another. Genetic analysis of the remains confirmed that they belonged to resident whales. All signs pointed to predation of resident whales by transient mammal-eating whales.

But researchers see it less as cannibalism than interspecific predation. Because although they live in the same waters, the two groups do not socialize or cross paths.

Learn more: These orcas wear salmon hats? It might not be as cute as you think

Incompatible in the North Pacific

Both resident and transient whales are long-time residents of the North Pacific and may have connections dating back hundreds of thousands of years. Transient whales first appeared once the waters became ice-free, coming in from the Atlantic. Residents arrived later in the area, needing to develop a close-knit family structure to protect against potential predation from passing whales.

“We are witnessing an evolutionary process: these two groups, which never mix, are becoming more and more distinct. At some point, they will be so different that they will become separate species,” Filatova said in the release.

Residents and travelers who call the North Pacific home are not the only groups to have such distinct traits. There are all sorts of other groups of whales around the world that feed on different prey and prefer different habitats.

A fateful gathering

As for the resident whales near Bering Island, some family members leave their immediate pod for an hour or two to search for other resident families. Many families even organize large gatherings to give young women and men the chance to find partners outside of their own family.

However, residents are widely dispersed during these gatherings, exposing themselves to predation from passing whales (although researchers note that reports of cannibalism by travelers are exceptionally rare). Just days before one of the severed fins was discovered, it emerged that several residents had organized a gathering that would end in the death of a family member.

Learn more: Whales are capable of establishing complex communications: could humans one day speak with them?

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