An orca has attacked a yacht off the coast of Scotland, U.K. — the first time this behavior has been recorded beyond Portuguese and Spanish waters. One expert believes it's a sign the boat-ramming behavior may have "leapfrogged" to a different orca population.
The orca (Orcinus orca) in Scotland repeatedly slammed into the boat's stern, where Wim Rutten, who was the only person on the boat, had attached a fishing line to catch mackerel.
Rutten said the orca seemed to be "looking for the keel," which is the part of the boat that orcas in Iberian waters have also targeted with ruthless efficiency. "Maybe he just wanted to play," Rutten told The Guardian. "Or look me in the eyes. Or to get rid of the fishing line."
Iberian orcas, a small and endangered population of about 39 animals, have sunk three boats in the last 18 months and damaged over 100 more by ramming into boats and ripping off their rudders. Some experts think an adult female named White Gladis may have survived a traumatic event — such as a boat collision or entrapment in a fishing net — that flipped a behavioral switch and triggered the first attacks.
Scientists have identified 13 orcas — 11 juveniles, White Gladis and another adult called Grey Gladis — that participate in these encounters and, in some cases, follow the boats all the way to port after breaking their rudders.
Related: Mystery orcas with bulbous heads wash up dead in unexplained mass stranding
The behavior appears to be spreading through social learning, with orcas imitating each other and reproducing acts they deem advantageous or interesting in some way, Alfredo López Fernandez, a biologist and representative of the Grupo de Trabajo Orca Atlántica, or Atlantic Orca Working Group (GTOA), previously told Live Science.
The latest incident, which occurred on Monday (June 19) off the Shetland Islands in the North Sea, may suggest orcas in the area have acquired the skill from their southern European neighbors.
"It's possible that this 'fad' is leapfrogging through the various pods/communities," Conor Ryan, a scientific adviser to the Hebridean Whale and Dolphin Trust, told The Guardian. (A fad is a behavior initiated by one or two individuals, which others adopt through social learning and then abandon.)
Although 2,000 miles (3,200 kilometers) separate orcas in the North Sea from the Iberian population, there might be "highly mobile pods that could transmit this behavior a long distance," Ryan said.
Experts with the GTOA suspect the attacks are linked to human activities at sea. Fishing, noise pollution and boat traffic, "even in an indirect way, are the origin of this behavior," López Fernandez told The Guardian.
The traumatic experience that may have sparked attacks off the Iberian coast was "perhaps related to a fishing boat while hunting tuna,'' Mónica González, a marine biologist working with the GTOA, told Yachting Monthly.
Every year, Atlantic bluefin tuna (Thunnus thynnus) pass through the Strait of Gibraltar on their migration path from spawning sites in the Mediterranean Sea to feeding grounds in the eastern Atlantic, according to a report by the European Parliament.
Encounters with orcas could be linked to these migrations, González said.
Bluefin tuna were overfished from the 1980s until 2010, but stocks have now recovered, according to the report. Nevertheless, experts think orcas may perceive boats as a threat to their food supply and survival.
"We think that the other orcas are juveniles and are copying [White Gladis'] behavior because she is an adult and they think that as an adult 'we need to do this to survive,'" González said.
