Orcas, also known as killer whales, compete with fishers around the globe for tuna. Until five years ago, there had never been any reports of attacks on boats. But since then, there have been repeated reports of the creatures ramming yachts, particularly in summer and spring. The orcas mostly target the rudders of the sailboats. The main focal point of the "interactions,” as marine biologists refer to them, occur in the Strait of Gibraltar and off Portugal’s Atlantic Coast. Fishers, residents, whale watchers and researchers are puzzled by their sudden aggressive behavior. Various theories have been put forward. Some think it might be linked to competition over tuna, which migrate from the Atlantic to the Mediterranean to spawn in May before returning in July. Others suspect that it is some kind of revenge action for past injuries incurred. An older female, the leader of an orca pod, allegedly had bad experiences with boats and is teaching pod members to fight back. Many marine biologists believe it is just a kind of game. What is certain is that no one has actually been seriously hurt up to now — not even on the yachts that sank, which begs the question: Are humans even the main target?