The first time orcas appeared near his catamaran, Florian Rutsch was surprised, but prepared.

Like many venturing around the Iberian Peninsula, Mr. Rutsch had browsed Facebook groups, Telegram chats and other online platforms where sailors have been swapping tips on a relatively recent phenomenon: How do you get orcas to leave your boat alone?

In May, when the crew of his catamaran, which he charters for high-end voyages and retreats, encountered an orca group while crossing the Strait of Gibraltar, he tried some of those ideas. He scattered sand in the water, which some sailors thought could act as a deterrent (unsubstantiated). Then he slammed the engine into full throttle, moving away from the group (advice supported by the Spanish government).

The orcas left them alone. But his second encounter with the animals in November was less civil.

This time, to deter them, the crew also tried another idea that had been passed along: booming a curated playlist of heavy metal — titled “Metal for Orcas” — through an underwater speaker. But the animals had moved quickly, targeting the rudder and disabling the boat’s steering. The crew had to call for help, and eventually Spanish rescue authorities arrived and towed the vessel to port.

“It is scary,” said Mr. Rutsch. “No one knows what works, what doesn’t work.”

‘It’s the talk of the town.’

Since 2020, orcas — apex predators that are the largest members of the dolphin family — have been disrupting the journeys of boats along the coastlines of the Iberian Peninsula, causing enough damage to a handful to sink them. Researchers don’t know why.

Online, some have been charmed by the schadenfreude of the orcas striking back at their yacht overlords, but biologists say it’s likely that the curious animals have simply learned a new way to play with boats.