Orcas, sometimes in groups, have been attacking boats off the coast of Spain and Portugal—leaving some sailors radioing for help. Researchers tell the Guardian that the behavior is highly unusual; while the killer whales that live in the waters of the Strait of Gibraltar often trail boats, they haven’t been known to attack, particularly in such an orchestrated fashion. The last reported attack was on Friday when an orca rammed the stern of a yacht 15 times, with such force it lost steering. In late July, a 46-foot vessel lost its rudder when orcas rammed the hull for more than an hour.