Two severed killer whale fins found on a remote Russian island may point to a gruesome new behaviour never seen before: orcas actively hunting and eating their own kind. That’s because each of the fins, a new study says, bears tooth marks from another killer whale.
When Dr Olga Filatova, an associate professor at University of Southern Denmark, received the photos from her long-time collaborator Sergey Fomin, she was fairly certain what she was looking at.
“When he found the first one, it was very surprising,” she told BBC Science Focus. “We did not really think it would happen ever in our lifetime, but it looks like it did.”
Genetic analysis confirmed that both fins came from resident killer whales – fish-eating mammals that live in tight, multigenerational family groups. The most likely culprits are transient killer whales – a distinct population sharing the same waters, but specialising in hunting marine mammals such as seals, sea lions and other whales.
Technically, this qualifies as cannibalism as there’s only one killer whale species, taxonomically speaking – the Orcinus orca.
But Filatova argued the reality is more complicated. Residents and transients don’t socialise or interbreed, and in the wild, they may not really recognise each other as the same animal at all.
Filatova believes the attacks most likely occurred during large social gatherings, when dozens of resident families congregate to breed. Because all members within a family group are related, killer whales must seek mates elsewhere – leading to sprawling assemblies that can span several kilometres.
During these events, juveniles can become separated from the protective close-knit family unit. “I think this is the easiest way for mammal-eaters to attack the young ones, just because everybody else is busy,” Filatova said.
Fomin observed one such aggregation just days before discovering the second fin.
Both fins came from young animals, Filatova said. That the fins were severed and not simply gnawed is telling: killer whales hunting other species typically remove fins to access the flesh beneath, leaving them behind as low-energy scraps.
The findings have implications beyond the grim discovery itself. Filatova argued that predation pressure from transients may actually explain the famously tight-knit social structure of resident killer whale communities.
“These residents are so stable for a particular reason: they need to protect themselves,” she said.
She suggests the two populations first came into contact around 100,000 years ago, when resident whales – more closely related to Atlantic killer whales – colonised the North Pacific, entering territory already occupied by transients.
The extraordinary family cohesion seen in residents today may be the evolutionary result of that long-running predation pressure.
With just two fins to go on, Filatova is cautious about drawing firm conclusions. Whether this represents a recent behavioural shift or something that’s always occurred undetected, she said, is still unknown.
Read more:
- Killer whales have now learnt a genius way to destroy great white sharks, new footage shows
- This mysterious gang of killer whales is hunting down and eating dolphins
- Killer whales filmed using tools for the first time – and scientists are stunned
