Orcas have been ramming and sinking luxury yachts in European waters for the past four years and scientists have been puzzled by the behavior. Now, research by a team of biologists, government officials, and marine industry representatives has shed light on the phenomenon, determining that the attacks are far from malicious.

The study reveals that young orcas, particularly juveniles and teenagers, engage in boat-bumping purely out of curiosity and playfulness, New Atlas reports. The behavior aligns with the orcas’ known tendencies to exhibit peculiar, isolated behaviors from time to time.

“Killer whales are known to play with other objects or animals in their environment to the point of damaging them (in the southern resident killer whale population of Washington, USA, which feed on salmon, individuals will ‘play’ with harbour porpoises to the point of killing them, which may be a similar escalation of an initially less harmful interaction), so this behaviour seems on that spectrum,” the scientists wrote in a report.

Data collected from individual orcas and observational studies indicate that the so-called attacks typically involve a few animals at a time, primarily from a core group of 15 orcas known for their boat-bumping antics. Notably, the majority of these orcas are male juveniles and teens, the most curious and exploratory members of the population.

The behavior was first observed around 2017, initially involving gentle head-bumping on boat rudders without causing any damage. As these orcas have grown larger, their playful activities have become more damaging, leading to the current situation.

Interestingly, no orca over the age of 25 — when males reach full maturity — has been seen participating in the attacks. Scientists believe that younger orcas may have learned this behavior by observing older siblings playing with rudder ‘toys.’ Some female orcas have been spotted during these activities, but researchers suspect they are there primarily to supervise the younger ones.