An unusual, dangerous game of catching and crashing into small sailboats and fishing boats is spreading through the population of orcas along the Spanish coast.
Scientists say at least 20 Iberian orcas have now learned the behavior by imitating their elders.
One or two orcas are believed to have begun interacting with and destroying small sailing vessels in 2020.
Scientists told the BBC that the animals appeared to be "playing" with the boats rather than behaving aggressively.
"That is just a game. It's not revenge against the boats, it's not climate change, it's just a game and nothing more," says Dr. Reno De Stefanis, a scientist working on the southern coast of Spain.
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Doctor De Stefanis is the president Cetacean conservation, information and research (CIRCE), a marine conservation organization.
He says orcas, also known as killer whales, appear to be playing a "game" centered on the boat's rudder - the part of the moving steering apparatus in the water.
He and his colleagues have now attached satellite tracking tags to the fins of two of the fewer than 60 animals in this population, which critically endangered.
The Spanish government uses maps of their movements to help inform sailors how to avoid these marine mammals, which hunt tuna along the coast of Portugal and Spain, and through the narrow Strait of Gibraltar.
Toys in the sea
French sailor Lou Lombardi himself encountered orcas near Gibraltar in July.
He and the rest of his crew watched for 80 minutes as five of these animals pushed and turned his ship, pounding on the rudder until it disintegrated.
As he and his colleagues prepared to return the repaired ship to the shipyard in Barbate, Spain, he told us the encounter seemed more playful than aggressive.
"There's foam in the rudder that goes into the water," he explained, "and the orcas pushed it around with their noses - like it was a toy."
"I had the feeling they were training each other," he told us.
"There were two cubs, and the adult orca would do it, and then she would watch the cubs repeat it - as if they were conveying something."
Orcas are known for being extremely friendly animals.
Other subspecies of killer whales have been recorded playing with floating seaweed, fiddling with fishing gear, and one population in the Pacific even appears to have gone through a phase of carrying dead salmon around on their heads.
Using ship's rudders as toys is a new type of behavior and is currently limited to this small, endangered Iberian population, but the young animals do seem to be mimicking the adult orcas.
By studying the footage and photos taken by the sailors, the scientists recognized some of the animals that took part in it.
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Monica Gonzalez is a marine biologist with the organization Orca Iberica, which records and maps orca encounters reported by vessels.
"Adults are very focused. They are focused on the helm and only the helm.
"But the cubs seem to be approaching, moving away, exploring the whole boat. It's a very different kind of behavior," she explains.
"We are intruders"
These large, intelligent and now problematic marine mammals are causing confusion and division among both the marine and scientific communities along this stretch of the Atlantic coast.
Some scientists have suggested that one female orca began "attacking" ships out of revenge after being injured by a vessel.
There is an ongoing debate on social media among sailors, some of whom are suggesting methods to defend their ships, such as throwing firecrackers into the water if the orcas begin to approach.
Dr. De Stefanis, who has been studying these marine mammals since 1996, hopes his tagging and tracking will point mariners to "killer whale hotspots" to avoid.
"They have a habit of staying in the same place for two, three hours, because they are looking for tuna," he explains.
"And that's why the official advice from the Spanish government is not to stop if you see orcas - get away from the area as quickly as possible."
This, however, is in direct contradiction to last year's advice and the current recommendations of the Portuguese government, which state that if you see an orca approaching, stop your boat immediately.
The idea behind it, explains Monica Gonzalez, was to be as boring as possible.
"Don't move the rudder, don't throw anything, don't shout," she said.
The orcas should just get bored and go away.
Dr Luke Randell, a marine mammal expert at the University of St Andrews, is not optimistic that sailors will simply be able to bypass defined hotspots of orca activity.
"There is a risk that it will escalate and the sailors will take matters into their own hands," he says.
"When all is said and done, if we want this behavior to stop, we have to get the ships out of that environment."
"It's a radical step for us as a species — to say we're going to limit our own behavior for the benefit of someone else."
Dr Randell believes that, in the future, there may be economic, rather than scientific, reasons for some boats to avoid the waters - and perhaps avoid sailing them during the season - where most of these encounters occur.
"Insurance companies might be interested in this," he says.
"Additional premiums may be required for navigation in these waters, which could reduce the density of navigation there. That could be the most favorable outcome for the orcas."
Watch the video: Orcas are very social creatures
Meanwhile, while sailors and the fishing industry try to figure out how to avoid these animals, tourists on the coasts of Spain, Portugal and Gibraltar are paying to go on whale-watching excursions to see them.
Nuria Riera, an artist living in Tarifa on the southern coast of Spain, who volunteers for a conservation and whale watching organization Firm, says the language used to describe orca behavior is simply not fair.
"Scientists don't even know why they do it," she says.
"And then I read reports of orcas attacking - it's very aggressive language.
"We must not forget that the sea is their home - we are intruders," she says.
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Additional reporting by Juan Dominguez
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