Why are killer whale attacks on the rise? These scientists set out to find out.

ON BOARD A BOAT IN THE STRAIT OF GIBRALTAR - From the surface, the azure waters seem calm and inviting in this narrow stretch where the Atlantic Ocean meets the Mediterranean Sea.

The barren coast of Spain looms in one direction; the tip of Africa in the other, less than 10 miles away. From time to time, schools of small fish leap out of the water in unison, as if in symphony.

But with binoculars trained on the horizon, the boat's captain keeps his eyes peeled for something possibly even more terrifying: orcas, also known as killer whales, which have ...