Why are orcas ‘attacking’ fishing boats off the coast of Gibraltar?

After an orca attack Elisabeth Heigl Berger & Markus Berger, a rescue boat was called.
MARTIN EVANS was a sailor traveling to Greece when he saw the orcas. He was 80 kilometres away from Gibraltar on 17 Juni. He says that he knew right away that there was a problem. I got on the helm and attempted to steer the boat by hand, but the boat was taken from me with great force.

About a dozen killer whales orcas circled the boat for 2 hours, banging on the bottom. One point I glanced at the bottom.