Evidence Suggests Rare Orca Cannibalism in North Pacific

Researchers studying killer whales in the North Pacific have uncovered evidence suggesting that orcas may occasionally prey on other orcas, a behaviour rarely documented among the ocean’s top predators.

The clues come from two severed dorsal fins discovered on Bering Island in Russia’s Commander Islands. The fins bore clear tooth marks and other signs of feeding damage, indicating they may have been torn from killer whales and partially consumed.

The findings, reported in the journal Marine Mammal Science, may help explain longstanding questions about the different social structures seen among killer whale populations.

Unusual beach discoveries

Marine biologist Sergey Fomin from the Pacific Institute of Geography found the first dorsal fin in 2022 while walking along the coast of Bering Island. Initially accustomed to seeing remains of prey species such as beaked whales and minke whales washed ashore, he was surprised to encounter the fin of a killer whale instead.

Two years later, another similar fin appeared on the same stretch of coastline.

Both fins showed bite marks consistent with attacks by other orcas, suggesting the animals had been preyed upon rather than dying naturally.

Genetic analysis later indicated that the fins belonged to resident killer whales, a population known for its stable family groups and fish-based diet.

Different hunting lifestyles

In the North Pacific, two major forms of killer whales coexist but behave very differently.

Resident orcas live in large, stable family groups and primarily feed on fish. Transient or Bigg’s orcas, by contrast, are nomadic predators that hunt marine mammals such as seals, dolphins and other whales.

Scientists suspect the severed fins may represent cases where Bigg’s orcas attacked resident killer whales, potentially treating them as prey.

Social structure puzzle

The possibility of cannibalism has led researchers to revisit a long-standing mystery in killer whale biology: why resident populations form unusually tight family groups that persist for life.

Many toothed whale species live in more fluid social groups similar to those of transient orcas. Resident killer whales, however, remain in extended maternal family units, sometimes numbering dozens of individuals.

Researchers speculate that such strong social cohesion may offer protection against attacks from other orca populations.

Rare but possible

Direct evidence of orca cannibalism remains extremely rare, and scientists caution that the exact circumstances of the deaths are uncertain. It is possible that the whales died from other causes and were scavenged afterward.

However, the bite marks and partial consumption of the fins suggest active predation is plausible.

Even among apex predators, opportunistic feeding can occur when food is scarce or when vulnerable individuals become available.

If confirmed, the findings highlight the complex and sometimes brutal ecological interactions that can occur even among the ocean’s most intelligent and socially sophisticated mammals.