Biologists have observed instances of orca-on-orca predation in the North Pacific, shedding light on the phenomenon of cannibalism among these marine mammals. This behavior may offer an explanation as to why some orcas travel in large family groups.
In the North Pacific, there are two distinct subspecies of orcas – transient or Bigg’s orcas and resident orcas. Transient orcas are nomadic hunters that form fluid hunting pods to prey on seals, dolphins, and other whales. On the other hand, resident orcas live in large family groups based on maternal ties, remaining with the same family throughout their lives. Residents exhibit a unique social structure where they disperse to feed individually on fish and regroup when resting or traveling.
While it was believed that the two subspecies rarely interacted, Sergey Fomin from the Pacific Institute of Geography in Russia discovered evidence of violent encounters. Walking along the beaches of Bering Island, Fomin stumbled upon gnawed-off dorsal fins of Baird’s beaked whales and minke whales, indicating predation by orcas. Surprisingly, he found bloodied and tooth-marked orca fins on two separate occasions, which genetic testing revealed to belong to southern resident orcas. It is speculated that these whales were likely consumed by Bigg’s orcas.
The reason behind the large family groups formed by resident orcas has puzzled scientists for some time. Olga Filatova from the University of Southern Denmark, along with Fomin and Ivan Fedutin, proposed a theory that these groups provide safety in numbers against potential predators like other orcas.
While orcas are top predators and rarely face threats, they have been known to be chased away by smaller pilot whales and exhibit aggression towards each other. Instances of cannibalism among orcas, as witnessed by researchers, raise questions about the circumstances that may drive these behaviors. Filatova suggests that when common food sources like fur seals and sea lions are scarce, orcas may turn to cannibalism as a last resort.
Researcher Jared Towers from Bay Cetology in Canada acknowledges the unique social structure of resident orcas as a defense mechanism, although he remains cautious about definitively attributing the observed cannibalism to these marine mammals. The possibility of post-mortem scavenging or sparring injuries cannot be ruled out.
In conclusion, the phenomenon of orca cannibalism sheds light on the complex behaviors and social dynamics within these marine mammal populations. Further research is needed to understand the factors driving such behaviors and their implications for the conservation of orca populations in the North Pacific.
