Scientists and marine enthusiasts alike have been captivated by an intriguing phenomenon in recent years: orcas bumping boats — sometimes resulting in damage or sinking. Beginning in 2020 in waters off the Iberian Peninsula, a subpopulation of orcas started ramming vessels and attacking their rudders. The actions have mostly targeted medium-sized sailboats that travel slowly through the Strait of Gibraltar and the coasts of Portugal, Morocco, and Galicia.

Since 2020 there have been more than 500 physical encounters. In approximately 250 instances, the orcas have caused physical damage, including the reported sinking of three boats.

When an orca and a vessel have made physical contact, the pod usually approaches from the stern. Interactions usually occur at the rudder and involve biting, ramming, and nudging. Orcas have also been seen rotating the rudder and, in certain situations, turning the vessel nearly 360 degrees by pushing the rudder with their heads or bodies.

Some boats reporting physical contact discovered the orcas had raked the bow, keel, and rudders with their teeth. More severely damaged rudders were bent at the stocks, completely detached, or split in half. There have been reports of at least one orca using its teeth to rip off a boat rudder.

Why this happens is up for debate.

One hypothesis, and by far the most unanimous amongst experts, suggests that the orcas are engaging in playful behavior.

“I think that these are really intelligent, curious animals, they like to interact with things in their environment,” Deborah Giles, the science and research director at the nonprofit Wild Orca, located in Washington State, told ZME Science. “I really believe that this is not an aggressive thing towards humans or towards boats.”

Orcas have a preference for sailboats with extending keels and rudders. This focus on specific boat types implies that the orcas are drawn to these structures rather than interacting with any vessel randomly. It’s also important to stress that fishing boats and private vessels receive different treatment, suggesting orcas are not interested in harming people or other vessels.

The primary consensus is that one orca in the area started the boat-bumping behavior and then benefitted from the interaction with the rudders by receiving something enjoyable, such as bubbles on their faces. A pleasant experience or vibrations could serve as this positive reinforcement, encouraging the orca to repeatedly interact with the keel or rudder of the boat. Experts concur that highly intelligent animals frequently learn through positive reinforcement, and it’s plausible that this behavior has proliferated within the orca community because of mutual observation and learning.

“Orcas pick up behaviors from each other,” Giles said. “It’s likely that one did get some sort of positive reinforcement from that interaction with boat rudders or the keels, whether it was a vibration or latching on to it to be taken along for a ride. Then it just kind of spread through the population.”

Is boat bumping just an Orca fad?

Boat bumping is most seen in younger orcas, indicating that it may be a behavior restricted to particular age groups within the population. It is not a common behavior among orcas; instead, it is referred to as a “fad” in the orca community. Marine biologists emphasize some behaviors are persistent and long-term, while others come and go, much like trends among human societies.

An infamous example was in 1987 when a female in the Pacific Northwest’s Puget Sound was seen wearing a dead salmon on her nose. Over the next few weeks, individual orcas within three area pods were seen wearing salmon hats. Much like many other styles from the 1980s, it has not been observed in mass since (though, like all bad fashions, at least one has tried to bring it back).

Eric Shaw of the Helping Hand Trust, a marine life conservation organization located in Gibraltar, says he thinks the behavior is protective.

“I think this is protective behavior that is taking place,” he writes. “The first report was from the coast of Portugal and in the Bay of Biscay. These areas are well known for Tuna following the fish along the continental shelf at this time of year. In the marine world, we know food follows food, and fingerlings of smaller species are moving into deeper water where they become prey to larger species, onwards and upwards to the largest within the ocean. The reports stated that sailing vessels were being attacked. When a monkey bites you or a dog, we humans always say we have been attacked, but one question that needs to be answered is if the ‘attack’ was provoked in some way.”

The idea of “Revenge of the Killer Whales” has become a hot topic, suggesting that these boat attacks might be the result of past trauma.

“I definitely think orcas are capable of complex emotions like revenge,” stated Monika Wieland Shields, director of the Orca Behavior Institute, in an NPR interview. “I don’t think we can completely rule it out.”

Though Shields also said she is not completely ready to sign on to the “revenge” notion. She states that despite humans having “given a lot of opportunities for orcas to respond to us in an aggressive manner,” there are no other examples of them doing so.

The revenge hypothesis supposedly began when an orca called “White Gladis” was hit by a vessel, becoming enraged and attacking the boat. This, in turn, triggered similar behavior among other orcas.

Some experts are afraid boat bumping will be seen as a sign of aggression and plead with vessel owners not to take aggressive action toward the orcas.

In an open letter, 30 scientists cautioned against “projecting narratives onto these animals,” stating, “In the absence of further evidence, people should not assume they understand the animals’ motivations.”

Right now, however, most just see it as a curiosity and a phase. Orcas are not known for attacking humans in the wild and to date, none have harmed boaters themselves.