Machi Yoshida // Naturalist Charters
New research suggests that resident killer whales in the North Pacific are occasionally attacked by Bigg’s killer whales. This cannibalism should even help explain differences in species group sizes.
After it was discovered that orcas are scaring off white sharks off the coast of South Africa with the constant massacres in which they eat their livers, new research has revealed yet another point in common between the whales and the famous serial killer Hannibal Lecter: o cannibalism.
The new , published February 24 in the journal Marine Mammal Science, focuses on two distinct types of orcas that share the waters of the North Pacific: resident orcas, which feed mainly on fish and live in large groups, and Bigg’s orcas, also known as transient orcas, which hunt marine mammals and tend to travel in smaller groups.
Although it was long believed that the two types avoided each other, scientists have discovered evidence to suggest that the two types avoid each other. encounters can be fatal and even result in mutual predation.
The investigation began in August 2022, when researcher Sergey Fomin found a severed dorsal fin of an orca on a beach on Bering Island in eastern Russia. The fin was bloody and marked with tooth impressions characteristic of killer whales, similar to a rake. Similar bite patterns have previously been observed on carcasses of prey species such as Berardius bairdii e Balaenoptera acutorostrataboth known to be targets of mammal-predating orcas.
Two years later, Fomin discovered a second fin, also with similar teeth marks. Genetic testing revealed that both fins belonged to southern resident orcasa piscivorous population found near Washington state and British Columbia.
The findings suggest that the resident orcas were likely attacked and devoured by Bigg’s killer whales. Although the authors believe that such incidents are not common, they are nevertheless signs of cannibalism between different ecological types.
If that’s the case, the threat could help explain why resident killer whales form exceptionally large and cohesive family groups. Many species come together to protect from predatorsand the grouping could allow residents to collectively drive smaller groups of orcas away from Bigg, says .
However, not all scientists are convinced. Some warn that teeth marks can also result from necrophagy or food post-mortemrather than active predation. Others point to alternative explanations for the evolution of the social structure of resident orcas, including cooperative hunting and the transfer of knowledge about local prey and habitat.
Still, the parallels between resident orcas and other highly social cetaceans are striking. The Globicephala melas groups, for example, are also known as confront and scare away the orcaspossibly as a defensive strategy.
The study suggests the theory that predation pressure may have shaped the social organization of resident orcas tens of thousands of years ago and what humans would call cannibalism may not be perceived in the same way by whales, as rarely interact socially and they can effectively see themselves as different species.
