The majority of the “disruptive” interactions between orcas and boats off the Iberian Peninsula in the past few years — López Fernandez said they numbered in the hundreds — have been brief and caused minimal physical damage to the vessels, according to a report co-written by López Fernandez and published in the journal Marine Mammal Science. But on at least three occasions, including one incident this month involving a sailing yacht, the orcas have sunk the boats.

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The female orca, whom scientists named White Gladis, appears to have taught the aggressive behavior to other adult orcas, whose children have begun imitating the behavior, López Fernandez said.

In most of the interactions, the orcas strike the rudder or hull, the underbody, of the boat, according to the report, which included interviews with sailors and other witnesses to the phenomenon.

Aside from “some punctual aversive incident” that may have triggered the attacks, the report said they may be caused by factors like loss of prey or disturbances by boats. Otherwise, the report said, it may just be because of the killer whales’ “natural curiosity.”

Orcas are known to be extremely intelligent and capable of teaching one another certain behaviors, including actions that could be interpreted as violent. One episode in 2016 involving an orca drowning another’s calf left scientists “horrified” as they described a “first of its kind” observation of orcas carrying out infanticide, which has been documented in other species.

‘Fascinated and horrified’ scientists watched as a killer whale drowned another orca’s calf

Another report published in Marine Mammal Science documented orcas attacking, killing and then eating blue whales. Jeremy Goldbogen, a biologist who studies whales at Stanford University, told Stanford News the coordinated killings were “arguably one of the most dramatic and intense predator-prey interactions on the planet.” The phenomenon “astounded” scientists, one marine biologist told the New York Times.

So what should be made of the coordinated attacks on boats? The report warned that if the situation “continues or intensifies, it could become a real concern” for the safety of sailors, but also for the orcas, which are endangered in the region, because they could harm themselves by attacking the boats or be harmed by sailors trying to protect their vessels.