Killer Whales May Hunt Other Killer Whales

Killer whales are often regarded as the ocean’s supreme predators, sitting at the highest level of the marine food chain. However, fresh evidence indicates that, for some killer whales, the most serious danger may be posed by other killer whales.

Scientists examined two detached dorsal fins marked with deep tooth wounds inflicted by another killer whale. These remains offer unusual physical proof that one killer whale killed and ate another.

The finding is leading researchers to reassess relationships between distinct killer whale groups and consider whether these confrontations influence their social structures and evolution.

Dorsal fins expose a killer whale attack

Two damaged dorsal fins were found in 2022 and 2024 on an isolated part of Bering Island, in Russia’s Commander Islands, roughly 2 kilometres from one another.

Whale researcher Olga Filatova, from the University of Southern Denmark (SDU), studied photographs of the fins and identified the characteristic depth and spacing of killer whale teeth in each one.

Both fins had sharply torn flesh and bite marks indicating a violent assault, rather than the gradual deterioration associated with decomposition.

Taken together, the wounds provided rare material evidence that a killer whale had been attacked and killed by another killer whale.

Signs left by a predator

Measured at the shoreline, one fin was around 47 centimetres high, whereas the other measured approximately 71 centimetres.

Deep channels across both remains matched killer whale teeth, while the incisions pointed to an exceptionally forceful ripping action.

“Also, if it was just aggression, they wouldn’t bother to tear off the fin,” said Filatova.

Because dead killer whales normally sink rapidly, scavenging is improbable. Genetic evidence in the skin remaining on the fins identified the type of killer whale that had been consumed.

Using mitochondrial DNA – genetic material inherited chiefly through mothers – the SDU researchers linked both samples to resident killer whales from the area.

This finding dismissed the most straightforward explanation: that the fins had belonged to a Bigg’s killer whale killed during a hunt. Once the prey had been identified, attention moved from whether the incident occurred to its possible implications for killer whale social life.

When killer whales prey on their own species

Every killer whale remains classified within one species, Orcinus orca, so the killing and consumption of one by another technically qualifies as cannibalism.

Nevertheless, taxonomists have recently designated Bigg’s killer whales and resident killer whales as separate subspecies within that species.

Their distinct diets and social customs separate these groups, meaning that one whale may not perceive another as a relative.

From this perspective, cannibalism may be a technical label, whereas predation more accurately reflects what occurs underwater.

Family groups shaped by protection

Resident killer whales around Bering Island form matrilineal families headed by females, and both male and female offspring remain with their mothers throughout their lives.

The group is held together through food-sharing and collective defence, while younger whales stay close to older relatives they already know and trust.

Four generations may travel as one, with adults generally departing only briefly to breed before rejoining their mothers. When facing a predator familiar with their anatomy and behaviour, resident whales benefit from having numerous relatives nearby.

Close genetic links also increase the likelihood of such defence, as accepting the risk of injury to aid a close relative still safeguards shared genes.

“Most likely, this predation pressure forced them to develop their unique, tight-knit family structure, where they protect each other and thus increase their chances of survival,” said Filatova.

Should predators have helped produce this family arrangement, scientists may have to reconsider behaviour that seems to be merely social loyalty.

Bigg’s killer whales and their hunting strategy

Bigg’s killer whales, which feed on mammals, commonly travel in smaller groups, and many adults separate from the family into which they were born. Since hunting seals and porpoises depends on stealth, smaller and quieter groups can improve the success of each pursuit.

“For the transient groups, the resident killer whales are simply prey,” said Filatova after reviewing local records and photographs of the fins.

At particular times, multiple resident families assemble in the same waters, allowing young whales to encounter mates beyond their own family line.

Yet protection is reduced as relatives become more widely dispersed. A hunting group could isolate an individual whale before its family can intervene.

Just days after one of these gatherings, Russian whale researcher Sergey Fomin found a bitten fin on the shore. Although these meetings may allow resident whales to avoid inbreeding, they can also produce short periods in which family protection is stretched thin.

An evolutionary divide in progress

Across hundreds of thousands of years, separation can send animal groups along distinct evolutionary routes, particularly when they become specialists in different prey.

Diet can influence body size, hunting methods and even social traditions. Learned behaviours may also diverge when groups no longer interact.

“We are witnessing an evolutionary process: these two groups, which never mix, are becoming increasingly distinct,” said Filatova.

Later research could establish whether this same trend occurs among other killer whale populations specialising in tuna, sharks or even other whales.

Ultimately, a torn fin found on a remote coast connected feeding behaviour, social relationships and the shortcomings of neat species classifications.

As further sightings and genetic samples become available, researchers may discover how frequently these attacks happen and how rapidly the groups continue to diverge.