The boat-sinking orcas are back.

Around 9 a.m. Sunday near the Strait of Gibraltar, two people on board the roughly 50-foot Alboran Cognac reported blows to the vessel’s hull and saw damage to the rudder as water flowed into the ship, Spain’s maritime rescue agency said.

An unknown number of killer whales had struck again, after hundreds of such encounters in recent years.

Over the radio, responders told the two individuals to put on their life jackets, make sure their GPS locaters were turned on and prepare for emergency evacuation. In the meantime, Spanish and Moroccan rescue agencies began urgently working to save them, locating a nearby oil tanker and electing not to dispatch a helicopter.

After about an hour, that tanker rescued the pair 14 miles off Cape Spartel in northern Morocco, the Spanish Maritime Safety and Rescue Agency (SASEMAR) said in a news release. The boat was left adrift and soon sank.

Spain-based Alboran Charter confirmed its ownership of the sunken vessel and said the individuals were customers. The company declined to say more about what happened or who the clients were.

Iberian orcas sinking a ship is not new. Over the past four years, at least 15 orcas have interacted with hundreds of boats sailing in the waters off Portugal, Spain and Morocco, sinking a handful of vessels in seemingly coordinated ambushes. Some ships have been found with teeth marks; others appear to have been rammed by an orca’s head or body.

On average, there have been 168 interactions each year since 2020, according to Grupo de Trabajo Orca Atlántica, or GTOA, a research group studying the region’s killer whales. GTOA has tracked 26 interactions so far this year, down from 61 through a similar time frame in 2023.

It’s not clear why the orcas have recently bumped, bitten and sank vessels. Some scientists say they are simply being playful, or maybe are curious, or perhaps are coming after boats because of a loss of prey. A handful say the actions could actually be gratifying to the whales.

A leading theory, though, is one of vengeance.

This idea, advanced by a scientist who has studied the encounters, posits that a female orca suffered a traumatic run-in with a boat that led her to start attacking the vessels. And because orcas are intelligent marine mammals that learn behaviors like hunting together, others followed.

But there is disagreement over this theory.

Some scientists argue that the incidents shouldn’t be called “attacks” without knowing the whales’ motives. They fear that label could prompt retaliation by boaters, calling it potentially “harmful” to the critically endangered species with just a few dozen members.

“Science cannot yet explain why the Iberian orcas are doing this, although we repeat that it is more likely related to play/socialising than aggression,” a group of more than 30 scientists wrote in an open letter last summer. “ … When we are at sea, we are in the realm of marine life. We should not punish wildlife for being wild.”

The letter explained that orcas have been observed developing “cultural ‘fads,’” including carrying dead fish on their heads, and the incidents with the boats may be nothing more than a “fashion trend.”

SASEMAR warned that the risk of the encounters is highest between May and August, recommending that boats avoid the area between the Strait of Gibraltar to the Gulf of Cádiz to its west. It added that if a boat comes across orcas, it should not stop moving, and instead should head toward the coast and shallower waters. People should not approach the side of the boat and are barred from using measures that could injure or kill the whales.

“It is possible the behaviour, as previous fads have,” the scientists wrote, “will disappear as suddenly as it appeared.”