Exploring Cannibalism: Why Some Orcas Prefer Family Pods

Recent observations by biologists indicate the occurrence of orca-on-orca predation in the North Pacific, suggesting that such cannibalistic behavior may be a reason why certain killer whales travel in extensive family groups.

There are two primary subspecies of killer whales (Orcinus orca) in the North Pacific Ocean. Transient killer whales, commonly known as Biggs killer whales, are nomadic, forming dynamic hunting pods to pursue seals, dolphins, and other whales. In contrast, resident killer whales maintain large family-oriented groups and stay close to their maternal ties throughout their lives. These residents disperse to hunt fish individually but reunite for resting or traveling.

Though it is believed that the two subspecies rarely interact, Sergey Fomin from the Russian Institute of Pacific Geography has recorded instances of aggressive encounters. While walking along the eastern shores of Bering Island, he noted bite marks on the dorsal fins of beaked and minke whales, remnants of predation by hungry killer whales. However, during the summer of 2022, he discovered a bloodied orca fin on the beach—its origin would be revealed two years later.

Through genetic analysis, it was found that the fin belonged to a southern killer whale, leading Fomin and colleagues to hypothesize that it was likely consumed by a Biggs killer whale.

Most toothed whales, including killer whales, exhibit fluid social structures with their pods changing frequently. The mystery of why southern killer whales form large family units has sparked scientific intrigue. “I’ve been curious about their social structure for a while, as it’s quite unique among species,” notes Olga Filatova from the University of Southern Denmark.

Upon hearing about the findings of the two dorsal fins and the potential for cannibalism, Filatova was intrigued. It’s possible that resident killer whales band together in large numbers for protection. She, along with Fomin and Ivan Fedutin, has published a study discussing this hypothesis.

Killer whales, being apex predators, rarely experience harassment. However, they have been observed being chased off by smaller pods of pilot whales. They are also known to display aggression towards one another. In 2016, Jared Towers of Bay Cetology reported witnessing a pod of Biggs killer whales attacking and killing a newborn. Towers speculated that because the calf was not consumed, this aggression was likely aimed at inducing sexual receptivity in the mother.

While it’s uncertain if the whales at Bering Island were cannibalized, Towers believes that the unique social structure of the residents likely serves as a defensive mechanism. Experts cannot dismiss the possibility that the fins were damaged during sparring or that the whales were consumed post-mortem. However, because deceased orcas typically sink, this scenario is less plausible.

Researchers can only theorize the reasons behind cannibalism in killer whales, with Filatova suggesting it may arise from necessity. With fur seals and sea lions being common prey on Bering Island, a shortage of food may prompt whales to consider alternative sources. “When food is scarce and a young killer whale presents itself, what choice do they have?” she remarks.