Why do Orcas bully and kill porpoises in the pacific?

 Highly endangered Southern residents, orcas live a particular life, feeding almost exclusively on Chinook salmon and consuming around two dozen fish per day.

However, researchers have documented 78 instances of these strictly fish-eating orcas harassing porpoises in the Salish Sea, stretching from Washington State in the US to British Columbia in Canada.

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The orcas harass porpoises in various ways, including pushing, holding, balancing, slapping, and raking them with their teeth, sometimes even passing them along between pod members.

In 28 of the events, the orcas killed the porpoises, with no evidence of cannibalizing them. Observations indicated that all three pods of the orcas participated in this odd behavior, suggesting cultural transmission and social learning between the pods.

Scientists analyzed the antagonistic behavior towards porpoises, involving researchers at institutions in Canada, the UK, and the US, all working together to protect the highly endangered Southern Resident orca population of just around 75 individuals.

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Deborah Giles, a Southern Resident expert, explained how fish-eating orcas have vastly different ecology and culture from their marine mammal-eating counterparts, with the two populations occupying the same waters.

Analysis by Giles’ team came up with three possible reasons for the orcas’ strange behavior towards porpoises.

One possibility is this is a severe form of play, promoting group coordination, cohesion, and social affiliation. porpoise harassment is often a collaborative endeavor, involving multiple orcas of various ages in a game-like bid to keep the porpoises out of the water.

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The orcas have also been seen practicing hunting techniques by catching and playing with porpoises. Besides, Giles’ research group discovered evidence suggesting that when orcas harass porpoises, they might be trying to take care of weak or ill creatures as if they were their offspring.

This odd mothering behavior was observed previously in this population, even when they carried the dead bodies of their newborns on their noses for days.

Almost 70% of Southern Resident pregnancies terminate due to inadequate nutrition, according to Giles.

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Although orcas are not the only threat porpoises face, smaller dolphins, such as bottlenose dolphins, also regularly harass and kill them for no apparent reason.

Termed porpicide by experts, this is just one of the many odd behaviors that dolphins, orcas, and other marine mammals display around the world.