Updated May 15, 2024 at 10:49 AM ET
The crew of a sinking yacht was rescued off the coast of Spain this week after a pod of orcas apparently rammed the vessel – the latest "attack" by the marine mammals in the area that has left scientists stumped, several boats at the bottom of the ocean and scores more damaged.
The encounter on Sunday between an unknown number of orcas, also known as "killer whales," and the 49-foot sailing yacht Alboran Cognac occurred on the Moroccan side of the Strait of Gibraltar, the narrow passage linking the Atlantic and Mediterranean where the majority of such incidents have occurred in recent years.
The Alboran Cognac's crew said they felt sudden blows on the hull and that the boat began taking on water. They were rescued by a nearby oil tanker, but the sailboat, left to drift, later went down.
The sinking brings the number of vessels sunk – mostly sailing yachts – to at least five since 2020. Hundreds of less serious encounters resulting in broken rudders and other damage, Alfredo López Fernandez, a coauthor of a 2022 study in the journal Marine Mammal Science, told NPR late last year.
As NPR first reported in 2022, many scientists who study orca behavior believe these incidents — in which often one or more of the marine mammals knock off large chunks of a sailboat's rudder — are not meant as attacks, but merely represent playful behavior.
Some marine scientists have characterized these encounters over the years as a "fad," implying that the animals will eventually lose interest and return to more typical behavior.
The study co-authored by López Fernandez, for example, indicated two years ago that orcas were stepping up the frequency of their interactions with sailing vessels in and around the Strait of Gibraltar.
Some researchers think it's merely playful behavior
One hypothesis put forward by Renaud de Stephanis, president and coordinator at CIRCE Conservación Information and Research, a research group based in Spain, is that orcas like the feel of the water jet produced by a boat's propeller.
"What we think is that they're asking to have the propeller in the face," de Stephanis told NPR in 2022. "So, when they encounter a sailboat that isn't running its engine, they get kind of frustrated and that's why they break the rudder."
In one encounter last year, Werner Schaufelberger told the German publication Yacht that his vessel, Champagne, was approached by "two smaller and one larger orca" off Gibraltar.
"The little ones shook the rudder at the back while the big one repeatedly backed up and rammed the ship with full force from the side," he said.
The Spanish coast guard rescued Schaufelberger and his crew, towing Champagne to the Spanish port of Barbate, but the vessel sank before reaching safety.
The encounters could be a response to past trauma
López Fernandez believes that a female known as White Gladis, who leads the group of around 40 animals, may have had a traumatizing encounter with a boat or a fishing net. In an act of revenge, she is teaching her pod-mates how to carry out attacks with her encouragement, he believes.
"The orcas are doing this on purpose, of course, we don't know the origin or the motivation, but defensive behavior based on trauma, as the origin of all this, gains more strength for us every day," López Fernandez told Live Science.
It's an intriguing possibility, Monika Wieland Shields, director of the Orca Behavior Institute, told NPR last year.
"I definitely think orcas are capable of complex emotions like revenge," she said. "I don't think we can completely rule it out."
However, Shields said she remained skeptical of the "revenge" hypothesis. She said 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.
Deborah Giles, the science and research director at Wild Orca, a conservation group based in Washington state, was also cautious about the hypothesis when NPR spoke to her last year. She pointed out that killer whale populations in waters off Washington "were highly targeted" in the past as a source for aquariums. She said seal bombs – small charges that fishers throw into the water in an effort to scare sea lions away from their nets – were dropped in their path while helicopters and boats herded them into coves.
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