The discovery of mutilated orca remains on a remote Russian beach has prompted new questions about the behavior of ocean predators. In August 2022 and July 2024, a researcher found severed killer whale fins on Bering Island, located off Russia’s Pacific coast. Both fins bore distinct tooth marks matching those of other killer whales. This finding has ignited a scientific discussion regarding killer whale cannibalism and the evolutionary history of different orca groups.
While the idea of orcas hunting their own kind is unusual, the evidence from Bering Island suggests that fatal encounters may occur between distinct populations. Marine biologists are now examining how these interactions might influence the complex social structures of killer whales in the North Pacific Ocean.
The Discovery on Bering Island
Sergey Fomin, a researcher at the Pacific Institute of Geography in Russia, discovered the first bloodied fin in 2022. Two years later, he found a second dorsal fin just two kilometers away. The second fin belonged to a young male and featured identical tooth marks. Fomin shared photographs of the remains with Olga Filatova, a whale researcher at the University of Southern Denmark.
Subsequent genetic testing revealed that the severed fins belonged to resident killer whales. In the North Pacific, resident orcas are known for eating fish and maintaining exceptionally tight-knit family groups. These families are typically led by a female and can include up to four generations that remain together for life.
Filatova and her colleagues concluded that the resident orcas were likely attacked and eaten by transient orcas, also known as Bigg’s killer whales. Unlike residents, transient killer whales travel in smaller, looser social units and specialize in hunting other marine mammals, such as seals, dolphins, and different whale species.
A Disagreement Among Scientists
The interpretation of the Bering Island findings has generated disagreement within the marine biology community. According to Filatova, the tooth marks indicate active hunting by mammal-eating transient orcas. She argues that because fresh killer whale carcasses usually sink quickly, scavenging is an unlikely explanation. Furthermore, she notes that injuries from routine aggression among resident orcas typically appear on the sides of the animals rather than on the fins.
However, other experts remain unconvinced that the findings represent definitive proof of predation. According to Michael Weiss, the research director at the Center for Whale Research in Washington, the rake marks on the washed-up fins could have been caused by transient orcas scavenging on already dead whales. Weiss also suggested that the injuries might have resulted from non-lethal aggression by other resident killer whales while the animals were still alive.
Additionally, researchers disagree on whether these interactions shaped the social behavior of resident orcas. Filatova proposes that the threat of predation by transient orcas forced resident killer whales to develop their large, protective family structures hundreds of thousands of years ago. Conversely, according to Luke Rendell, a biologist at the University of St Andrews, there is currently not enough evidence to build a solid account of the social evolution of fish-eating orcas based on these observations alone. Rendell noted that the benefits of foraging together and sharing habitat knowledge could also explain why resident orcas form large groups.
Evolutionary Differences and Species Perception
Even if transient orcas are actively hunting resident orcas, the predators likely do not view their actions as cannibalism. Taxonomically, all killer whales are currently classified as a single species, known as Orcinus orca. However, the distinct groups in the North Pacific do not interact or reproduce with one another.
According to Filatova, transient and resident killer whales are so different that the transients likely perceive the residents simply as another type of prey. The historical separation of the groups supports this theory. Transient orcas originally migrated to the region from the Atlantic Ocean when the waters became ice-free. They were already established as specialized marine mammal hunters by the time resident orcas arrived in the area.
Because the two groups remain isolated from one another, some scientists argue they should be classified as separate subspecies. Off the coast of Bering Island, resident families occasionally spread out across several square kilometers during large gatherings to allow young males and females to find mates outside of their immediate families. According to researchers, one such gathering occurred just days before Fomin discovered one of the chewed fins, potentially leaving the resident whales vulnerable to an attack.
