An unknown number of orcas have sunk a sailing yacht after ramming it in Moroccan waters in the Strait of Gibraltar, Spains maritime rescue service said on Monday, a new attack in what has become a trend in the past four years.

The vessel Alboran Cognac, which measured 15 metres (49 feet) in length and carried two people, encountered the highly social apex predators, also known as killer whales, at 9 a.m. local time (0700 GMT) on Sunday, the service said.

The passengers reported feeling sudden blows to the hull and rudder before water started seeping into the ship. After alerting the rescue services, a nearby oil tanker took them onboard and transported them to Gibraltar.

The yacht was left adrift and eventually sank.

The incident is the latest example of recurring orca rammings around the Gibraltar Strait that separates Europe from Africa and off the Atlantic coast of Portugal and northwestern Spain.

Experts believe them to involve a subpopulation of about 15 individuals given the designation Gladis.

According to the research group GTOA, which tracks populations of the Iberian orca sub-species, there have been nearly 700 interactions since orca attacks on ships in the region were first reported in May 2020.

Researchers are unsure about the causes for the behaviour, with leading theories including it being a playful manifestation of the mammals curiosity, a social fad or the intentional targeting of what they perceive as competitors for their favourite prey, the local bluefin tuna.

Although known as killer whales, endangered orcas are part of the dolphin family. They can measure up to eight metres and weigh up to six tonnes as adults. (Reuters)