Orca fins washed up in the north Pacific may indicate cannibalism, a new paper published in the Marine Mammal Science journal suggests.
The fins bore tooth marks, and may explain why some orcas live in large family groups for protection, scientists say.
Orcas (Orcinus orca) or killer whales are one of the most widespread animals on Earth and were long considered as one species, according to the US NOAA Fisheries organisation.
However, biologists have increasingly recognised the differences between resident and Bigg’s killer whales, it says.
While resident killer whales maintain tight-knit family pods and prey on salmon and other marine fish, Bigg’s killer whales – named after Canadian scientist Michael Bigg who was first to describe the difference - roam in smaller groups, preying on other marine mammals such as seals and whales.
Bigg had noted in the 1970s that the two animals did not mix with each other even when they occupied many of the same coastal waters, which is often a sign of different species, NOAA Fisheries says.
Research published last month by Olga Filatova of the University of Southern Denmark and colleagues in Marine Mammal Science suggest that resident killer whales may occasionally be preyed upon by sympatric mammal-eating Bigg's killer whales.
They say that scavenging on the carcasses of dead resident killer whales cannot be definitively ruled out. Killer whales are known to exploit carrion, including feeding on a member of the same species killed by whalers during the commercial whaling era.
Read Marine Mammal Science here
