Reports of orcas striking sailing boats in the Straits of Gibraltar have left sailors and scientists confused. Just what is causing such unusually aggressive behaviour? When nine killer whales surrounded the 46ft boat that Victoria Morris was crewing in Spain on the afternoon of 29 July, she was elated. The biology graduate taught sailing in New Zealand and is used to friendly orca encounters. But the atmosphere quickly changed when they started ramming the hull, spinning the boat 180 degrees, disabling the autohelm and engine. The 23-year-old watched broken bits of the rudder float off, leaving the four-person crew without...