An unknown number of orcas rammed a sailing yacht in Moroccan waters in the Strait of Gibraltar on Sunday morning, causing it to later sink, the latest attack in a trend that has been terrifying sailors in the region for the past four years. 

The latest incident took place at around 9 a.m. when crew members aboard the 50-foot-long Alboran Cognac called rescue services for help, saying that their ship had been damaged by the apex predators about 14 miles from Cape Spartel, local outlet El Pais reports, citing Spain's maritime rescue service. Cape Spartel is located at the southern entrance to the Strait of Gibraltar.

A helicopter was mobilized and the oil tanker MT Lascaux which was sailing nearby was also asked to provide assistance.

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The tanker eventually rescued the two people 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 An Atlantic Orca Task Force (GTOA), which tracks populations of the Iberian orca subspecies, there have been nearly 700 interactions since orca attacks on ships in the region were first reported in May 2020.

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It is unclear why the orcas are targeting boats but some experts believe they may be acts of revenge.

Marine biologist Alfredo Lopez Fernandez told Live Science previously that the lead whale, a female orca scientists have called White Gladis, suffered a "critical moment of agony," likely a collision with a boat or entanglement with a fishing line, that turned her more aggressive. 

Other theories include it being a playful manifestation of the mammals' curiosity, a social fad or the intentional targeting of what they perceive as competitors for their favorite prey, the local bluefin tuna.

All but a handful resulted in only minor injuries or damage. However, the attacks have grown more frequent and a few have led to boats sinking.

For instance, in August last year, Phep Philouceros, 77, was sailing off the coast of Cape Vincent in Portugal, when his boat was attacked by orcas. The sailor, who has 55 years of experience, said the orcas continued for 30 minutes — even following the boat as it was towed to shore. He caught part of the attack on video. 

Fox News’ Peter Aitken and Reuters contributed to this report.