August 11, 2022 was an unusually calm day in the Bay of the Biscay. Onboard the sailing vessel Triola the Erichsen family didn’t fear the weather the bay had gained its ill reputation from. In the early morning the wind had died and Triola motored slowly, heading to A Coruña in northern Spain. There was barely a ripple on the water. But below the surface, orcas were advancing. One animal was moving towards the boat from the stern. Mikkel Erichsen, the skipper of Triola, didn’t see it. Another approached from the bow and when it surfaced, Erichsen glimpsed a dark triangular fin. The orcas moved in.

Since 2020, orcas around Portugal and Spain have wrecked more than 100 boats, sometimes ramming them full force with all the weight of their 6-to-8-ton bodies, other times hitting the rudder or biting it to pieces with their 3-inch-long teeth. In 2020, scientists counted 52 so- called ‘interactions’ between boats and orcas. In 2021 this number climbed to 197 and in 2022 to 207. Many boats were so badly damaged they needed to be towed to land for repairs. Scientists use the word interaction to signify that they don’t know the motives behind the unusual behaviour. Sailors, on the other hand, call the interactions ‘attacks’. In marinas in Gibraltar and Portugal and along the Galician coast in northwestern Spain all that is talked about is orcas.

My own experiences with orcas do not include the kind of interactions that boaters have endured in Spain and Portugal. As a marine biologist I have studied orcas in Norway for almost a decade, and I have spent countless hours observing them from boats. My fascination was spurred by the many examples of their playful and curious nature. When I read about the interactions in Spain and Portugal, I was instantly intrigued.

Over a video call, Erichsen tells me the story of the day it became his family’s turn to grapple with the feared whales. As a seasoned sailor he had set out with his wife and three children from Norway three months earlier on a year-long journey. He told me that to lessen the risk of an interaction, they had decided on a westerly course across the Bay of Biscay from Brest in France to A Coruña in Spain keeping the boat in waters over 4,000 metres deep. Most interactions with the orcas have taken place in shallower water, so staying in deep water for as long as possible seemed like a good strategy.

The strategy had worked well until August 11, when he saw the fin of an orca cutting through the water. “Seconds after I saw the fin there was a loud crash,” Erichsen explains, “the boat shuddered as if we had hit a rock.” He realised that another orca was under the boat whacking the rudder or the hull full force. Then he spotted a third whale. Underwater the three orcas took turns mauling the rudder. Each time the whales hit it, the steering wheel spun abruptly from side to side. The whales surfaced close to the boat, their exhalations sharp and powerful, sounding like explosions, before they submerged again. When Erichsen tried to manoeuvre the boat, he could tell that the steering was broken. “I had to call the coast guard and ask to be towed,” he says. The Triola’s rudder is equipped with two ‘stoppers’ on each side to prevent it from turning all the way around and hitting the hull. “I was concerned about the bashing and went below deck to check the hull from the inside,” Eriksen remembers.

He could immediately tell that both stoppers were either broken or ripped off. The orcas were turning the rudder all the way around and each time they pressed with all their weight on what remained of the rudder he could see the hull of the boat bulging inwards, swelling like a bad bruise. “That’s when I got really nervous”, he recalls. “It was below the waterline. If they managed to press so hard that they broke a hole, water would be pouring in. And it would come fast.” Shaken, Erichsen untied the life raft, so he could launch it quickly into the water if needed.

The Spanish coast guard arrived before it became necessary to get into the raft and towed Triola and the Erichsens to A Coruña. Even during the procedure to fasten the tow and after the Triola was being pulled behind the coast guard the orcas kept up their assault. In the marina Erichsen inspected the damage. The orcas had bitten large pieces off the rudder.

Understanding the orcas’ biology and behaviour are a priority for whale researchers in Spain and Portugal, and few know more about them than Dr Ruth Estaban, who has studied them for more than a decade. She is a researcher at the Whale Museum in Madeira, and I catch her on a video call late one evening. She looks weary, and I imagine that these days questions from national authorities, journalists, and frustrated sailors swamp her inbox and voicemail. But behind her black rimmed glasses her eyes smile when she admits that “yes”, she knows these whales quite well and “no”, she really hasn’t a clue why they have started wrecking boats.

What she does know is that the orcas in Spain and Portugal belong to a small and critically endangered population of only 35 individuals. Their main prey is Atlantic bluefin tuna, a popular catch also for the Spanish, Moroccan and Portuguese tuna fleet. The orcas are not above taking the tuna straight from the lines, biting chunks off the fish or ripping them off the hooks. Stealing from the longlines sometimes brings the orcas at odds with the fishermen. Although the information is unconfirmed there are reports from 2004 and 2005 of orcas being shot and killed, presumably by angry fishermen. However, there is little evidence that points to this as a motive for the orcas’ interactions with boats. Esteban tells me that now, for some reason, the orcas seem to have set their eyes on single hull sailing vessels.

Except for two isolated accounts of boats reportedly sunk by orcas in the Galapagos in 1971 and off eastern Brazil in 1976 researchers have never seen this kind of behaviour before. In newspapers, online news, and social media there is no lack of suggestions to explain the behaviour, but Esteban stresses that scientists don’t guess, they collect data, analyse them, and interpret them. In a recent study she and 14 of her colleagues in Portugal and Spain have summarised the different hypotheses.

One hypothesis for the behaviour leans on the fact that at least one of the interacting orcas has been observed with injuries. In July 2020, a juvenile orca was photographed with a semicircular wound in front of the white eyepatch. The wound healed well and later when the animal was re-sighted it was no longer visible. However, the same individual appeared in February of 2021 with a large row of scars on its back behind the dorsal fin. Both injuries could have been caused by interactions with boats. Esteban and the other scientists are not ruling out that one or several individuals have had what they call “an aversive incident” that triggered the whales’ interaction with boats. Such an incident could have been a dramatic or fatal collision with a boat for one or more of the orcas.

Another hypothesis condenses all the things that are wrong with the environment in which these orcas live and argues that the whales are responding to the combined stresses of these factors. The Strait of Gibraltar and the coasts along Portugal and Spain have significant levels of marine vessel traffic making the acoustic environment noisy and possibly stressful. Although their main prey, the bluefin tuna, was removed from the endangered species list in 2021, food may have been scarce for the orcas in previous decades and the orcas’ depredation of the tuna fishermen’s longlines sometimes leads to conflicts and dangerous interactions. Additionally, this population of orcas has markedly elevated concentrations of PCB and other pollutants contributing to deteriorating health and low breeding success.