The number of reported incidents involving orcas has risen over the summer months, with researchers noting that interactions between the whales and boats are not unusual, but the level of aggression displayed in July and August is "highly unusual."
Researchers speculate that it might be competition for tuna populations along the coast that has led to some distress among the whale populations. Alfredo Lopez, coordinator for the Study of Marine Mammals in Galicia, said orcas make their way up the coast each September to chase tuna.
Since 1999, two of five pods common to the area have learned to take tuna from fishermen drop lines, with several sustaining injuries from the lines as a result.
However, the events are still considered unusual.
"These are very strange events," says Ezequiel Andreu Cazalla, a cetacean researcher. "But I don't think they're attacks.
Rocio Espada, who works with the marine biology labratory at the University of Seville, said she was astonished by what she's heard.
"For killer whales to take out a piece of a fiberglass rudder is crazy," Espada said. "I've seen these orcas grow from babies, I know their life stories, I've never seen or heard of attacks."
Spanish maritime authorities have warned vessels to "keep a distance," but sailors have found that advice difficult to follow, with reports ranging from brief but sudden clashes to sustained ramming for over an hour.
Alfonso Gomez-Jordana Martin, a member of a delivery crew boat, said that their boat was brought to a halt by a pod of four orcas.
"Once we were stopped, they came in faster: 10-15 knots, from a distance of 25m," Martin said. "The impact tipped the boat sideways.
The skipper's report of the incident said that the force "nearly dislocated the helmsman's shoulder and spun the whole yacht through 120 degrees."