Researchers studying killer whales noticed that representatives of one of the fish-eating populations of these marine mammals often attack and kill porpoises, but then do not eat the prey. An international team of scientists from the USA, UK and Canada tried to explain the reasons for this behavior.

The study, published in the journal Marine Mammal Science, refers to a population of southern-dwelling killer whales that live near the Pacific coasts of the United States and Canada. Unlike other orca species, this group is in danger of extinction: There are only 75 individuals in the population. They feed on fish, preferring salmon and more specifically sea bream (Oncorhynchus tshawytscha), an endangered species.

Although southern resident killer whales eat fish rather than mammals, there is ample evidence that they stalk and kill porpoises (Phocoenidae) without consuming their prey.

To understand why killer whales do this, a team of scientists led by Deborah Giles of the nonprofit organization Wild Orca and Sarah Teman of the conservation society SeaDoc Society, collected and examined documented information on 78 whale species. sections. Cases were recorded from 1962 to 2020.

The analysis showed that killer whales of the southern population frequently attack young porpoises that are similar in size to adult porpoises. More young orcas of both sexes were observed engaging in this type of behavior, but there were not much fewer incidents involving relatives in other age groups. Scientists also found that behaviors were passed on by killer whales from generation to generation and from one population to another.

Experts offer three possible explanations

The first hypothesis is that chasing porpoises may be a form of social game. Like other intelligent species, these marine mammals play to bond, socialize, or just have fun. Such behavior contributes to the coordination of actions and harmonious work in the group.

According to the second hypothesis, attacks on porpoises are a form of training in which killer whales improve their hunting skills. Finally, the third version suggests that the behavior is related to the whales’ instinctive desire to help group members if they appear weak or sick. For example, there is evidence that female killer whales can “carry” the bodies of their dead calves. Some of the cases of porpoise harassment resembled this behavior.

However, researchers admitted that it is unlikely to determine the exact cause.

“Orcas are incredibly complex and intelligent animals. This behavior is a great example of orca culture,” said Sara Teman.

But scientists still made a definitive conclusion. The tradition of eating salmon is well-established among southern-dwelling orcas, so they are unlikely to eat porpoises. The study highlighted the importance of protecting salmon in orca habitat. The future survival and well-being of the southern resident killer whale population depends on how many of these fish there are.

Meanwhile, cases of killer whales attacking ships in the Iberian Peninsula region have become more frequent lately. It is known from media reports that in three cases the case ended with the sinking of the boats. Undoubtedly, killer whales of another population were active here, but scientists assume that they could converge with representatives of the population living in the south due to the tendency to playful behavior. Source