Hours into a journey to Portugal from Morocco, the crew of a 46-foot sailing cruiser noticed something was wrong with the rudder. Then, someone shouted what they saw slicing through the choppy waves: “Orcas! Orcas!”
The orcas kept pace with the boat, slamming into its side and chewing at the rudder, according to its skipper, a photographer onboard and video of the encounter. For about an hour, the crew signaled their predicament to the Spanish Coast Guard and tried to stay calm.
“There was nothing we could do,” said Stephen Bidwell, the photographer, who was two days into a weeklong sailing course with his partner when the ramming began. “You’re in awe at the same time as you are nervous.”
The skipper, Gregory Blackburn, said he wrestled for control of the boat as the orcas banged into it, interfering with the rudder. “It’s a reminder of where we are in the food chain and the natural world,” he said.
Eventually the boat managed to motor back to Tangier, Morocco. But marine scientists took note of the episode, on May 2, and said it continued a puzzling pattern of behavior by a small group of orcas off the Iberian Peninsula’s western coast. The orcas, according to the researchers, have caused three boats to sink since last summer and disrupted the trips of dozens of others.
Wild orcas, although apex predators that hunt sharks and whales, are not generally considered dangerous to humans. The animals, the largest of the dolphin family, have been known to touch, bump and follow boats, but ramming them is unusual, marine scientists say. A small group of orcas, numbering about 15, started to batter boats around Spain in 2020, with researchers calling the behavior uncommon and its motivations unclear.
“We know that it is a complex behavior that has nothing to do with aggression,” said Alfredo López Fernandez, a biologist at the University of Aveiro in Portugal who worked on a study published last June on the subject. The orcas show no sign of wanting to hurt humans, he said.
In most sightings, the orcas do not change their behavior or make physical contact, according to the Atlantic Orca Working Group, which began tracking direct interactions — as well as sightings — in 2020.
Since an initial surge that year, orcas have been documented approaching or reacting to vessels about 500 times, causing physical damage about 20 percent of the time, in the high-trafficked seas near Morocco, Portugal and Spain, the group said.
The orcas off the Iberian coast are considered an endangered population: The group arrives in waters near the Strait of Gibraltar every spring from waters deeper and farther up north up the coast to hunt tuna. But while they are a usual sight, scientists do not know how to stop the small group’s recent behavior, which has left sailors worried about safety and ship damage, and which has caught the attention of the Spanish and the Portuguese authorities.
“Every week there is an incident,” said Bruno Díaz López, a biologist and the director of the Bottlenose Dolphin Research Institute who was not involved in last year’s research. “We really don’t know the reason.”
In the most recent example, orcas battered a sailboat off the coast of Spain, causing it to sink in the early hours of May 5. The Spanish authorities quickly arrived, and the four people onboard were rescued “in good humor,” said Christoph Winterhalter, the president of the Swiss company that was operating the boat, Hoz Hochseezentrum International.
The University of Aveiro biologist, Dr. López Fernandez, said that it was possible that the three boats sank over the past year because they were vulnerable to leaks or not equipped to endure the damage. (“The condition of the boat was very good,” Mr. Winterhalter said of the one his company had chartered.)
The small group of orcas, including only two adults, were responsible for a majority of the interactions with boats, which number some 200 a year and range from the North African coast to France, according to Dr. López Fernandez.
Researchers do not know what is behind the behavior. Some have speculated that it is an “aversive behavior” that could have started after an incident between an animal and a boat, like an entanglement in fishing line, or an invented behavior from young orcas that is being repeated.
Those remain only theories, though Dr. López Fernandez said it appeared that the behavior might be passing between local animals.
“We know that orcas share their culture with their young and with their peers,” he said, adding that they learned from imitation. But because the behavior has been observed only in this particular subpopulation of orcas, he said that it was unlikely to pass onto distinct orca groups that populate waters around the world.
Given the lack of evidence and the presence of young orcas in the group, other scientists expressed skepticism that the behavior stemmed from a boat incident and believed that the animals may simply be playing.
“They’re getting some sort of reward or thrill from it,” said Erich Holt, an orca expert and research fellow with Whale and Dolphin Conservation, a wildlife charity. “Play is part of being a predator.”
Scientists say that aside from having sailors avoid the area, they do not know how to stop orcas from bothering sailboats, which tend to be quieter than most vessels and therefore more attractive to the animals.
It has also left conservationists worried about how humans will treat the orca population, especially as sailors in the region express growing frustration with the animals.
“I hope that they stop doing it as quickly as they started, because it’s actually imposing a risk on themselves,” said Hanne Strager, a marine biologist and the author of “The Killer Whale Journals,” adding that it was putting pressure on an already vulnerable species.
Mr. Bidwell, the photographer, said the episode would not stop him and his partner from booking another sailing trip in June, though perhaps with some changes. “Maybe we don’t go that same route,” he said.
