Scientists studying stranded whale remains in the North Pacific have discovered evidence suggesting that killer whales may sometimes prey on their own kind. The clues come from dorsal fins found washed up on beaches that were covered in distinctive orca tooth marks.
The findings point to rare instances of cannibalism among Orca and may help explain why some populations of these marine predators live in unusually large and tight-knit family groups.
The research was published in the journal Marine Mammal Science.
Two Different Types of Orcas
In the North Pacific, scientists recognize several distinct types of orcas that behave very differently.
Two of the most well-known are:
- Resident orcas – live in large family pods and mainly eat fish such as salmon
- Bigg’s orcas (transient orcas) – travel in smaller groups and hunt marine mammals like seals, dolphins and whales
These groups rarely socialize and were long believed to mostly avoid each other.
But the newly discovered evidence suggests their encounters may sometimes turn deadly.
The Discovery on a Remote Beach
In August 2022, researchers found a bloodied dorsal fin on a beach on Bering Island in Russia. The fin showed deep rake-like tooth marks consistent with killer whale bites.
Similar tooth-marked fins had previously been found on whales killed by mammal-hunting orcas. But this time, the fin belonged to another orca.
Two years later, scientists discovered a second fin from a young male killer whale with the same type of tooth marks.
Genetic tests revealed the fins belonged to southern resident orcas, a fish-eating population that lives near Washington State and British Columbia.
Researchers believe these whales were likely attacked and eaten by Bigg’s orcas.
Why Orcas Might Attack Each Other
The dorsal fin itself is tough and not very nutritious, which is why predators likely tore it off and discarded it while eating the blubber and muscle underneath.
Scientists emphasize that this type of cannibalism is probably very rare.
Still, even occasional predation could influence how different orca groups behave.
Safety in Numbers
Researchers think the threat from mammal-hunting orcas may help explain why resident orcas live in large, tightly bonded family groups.
In many animal species, forming large groups helps reduce the risk of predation.
Observations support this idea:
- Large resident pods have been seen chasing away smaller groups of Bigg’s orcas
- Bigg’s orcas sometimes avoid areas until resident pods leave
This suggests the strategy works.
Scientists Still Debate the Evidence
Not all researchers are convinced the tooth marks prove cannibalism.
Some scientists say the marks could also come from:
- Scavenging on dead orcas
- Aggressive interactions between whales
More evidence will be needed before scientists can fully confirm the behavior.
Orcas’ Complex Social World
Orcas are among the most intelligent and socially complex animals in the ocean. Different populations have unique cultures, diets and behaviors.
In fact, some researchers believe the differences between resident and Bigg’s orcas are so large that they may eventually be classified as separate species.
If that turns out to be the case, what looks like cannibalism may simply be one type of whale hunting another.
Either way, the discovery offers a fascinating glimpse into the hidden conflicts shaping the lives of the ocean’s top predators.