An unknown number of orcas sunk a sailing yacht in Moroccan waters in the Strait of Gibraltar on Sunday, according to Spain’s maritime rescue service. While orcas are typically peaceful, this is the latest in a string of attacks that have hit the region in the past four years.

Reuters reports that a 49-foot-long vessel, named the Alboran Cognac, carried two people and encountered the high social apex predators at 9 am local time on Sunday. The passengers reported sudden blows to the hull and rudder before the water started seeping into the ship. A nearby oil tanker rescued the two onboard and transported them to Gibraltar. The yacht was left to sink into the ocean.

Experts believe the orcas involved to be a subpopulation of about 15 individuals given the name “Gladis.” This group of juvenile males has sunk several yachts in the Strait of Gibraltar over the last four years, but experts are somewhat baffled as to why. While typically peaceful animals, the Gladis pod has plagued the small strip of water separating Europe and Africa for years.

There have been nearly 700 interactions between orcas and ships in the Strait of Gibraltar region since May 2020.