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Earlier this year, there were several reports of orcas severely damaging sailing boats in the Strait of Gibraltar – and they are at it again.

On 31 October, a pod of orcas surrounded a sailboat off the coast of Morocco. The whales nipped at the ship’s rudder and rammed the hull for about 45 minutes, according by the tour company operating the boat. The damaged yacht tried to make it back to shore, but ultimately sank near the entrance of a port.

Where is this happening?

In the Strait of Gibraltar – a strip of sea separating the southern tip of Europe from northern Africa. A pod of orcas there has rammed boats and ripped off the rudders, sinking four sailboats and damaging dozens more. The orcas began a wave of activity this May, and videos documenting the encounters have been sweeping the internet since.

At least a dozen whales are taking part in the activity, sparking a flurry of speculation over whether the orcas (Orcinus orca) may be teaching each other how to bring down boats and organising into an army. But non-combative reasons could be behind the apparent trend.

How long has this been going on?

The rise in whale encounters over the past year has captured public attention, but altercations with these orcas began earlier than this. Scientists, fishers and locals began reporting unusual encounters in the Strait of Gibraltar . According to the , which tracks this pod, there were 207 reported interactions in 2022. While many interactions were relatively harmless, at least four ships have sunk this year, with no reported injuries to people – all of whom were rescued before their boats went under.

Over the past few years, these orca-boat encounters in the Mediterranean seem to have escalated during the month of May, which is when the pod’s favourite food, bluefin tuna, is migrating through the area. That makes this latest confrontation distinct from the others.

What exactly are the orcas doing to boats?

In most cases, the orcas take turns quickly approaching the stern of the boat, with an apparent interest in the boat’s rudders, which they pierce or snap with their teeth. The whales have also been seen pressing into sailboats with their head and with the flanks of their body, occasionally tearing holes in the hull.

Sometimes, they cause no damage to the ships, instead riding in the boat’s wake. Notably, this group of whales seems less interested in large or motorised vessels. “They’re hyper-focused on sailboats,” says at the University of Washington in Seattle.

How many orcas are involved?

The encounters, including the latest one last week, usually involve only a handful of whales from a pod of around 39. Images and video of the events are helping researchers track which members of the pod are most involved and which have yet to exhibit the behaviour. Currently, around 15 orcas are partaking in the boat-ramming activity. “It’s a behaviour that has probably spread from one individual,” says at the University of British Columbia in Canada.

Can orcas learn from one another? Will this behaviour spread?

Orcas are a social species capable of learning from their podmates, so it is possible the behaviour is a trend that is catching on. But this doesn’t mean that the whales are intentionally teaching their podmates to target boats, which would require communicating a motive and recruiting others to the cause. Instead, it may just look fun or interesting to the orcas.

This North Atlantic subpopulation, like many orca pods, is distinct from others in diet, culture, dialect and genetics. Members of this pod don’t mingle with other orcas, so it is unlikely this behaviour will spread to other populations, though it could spread further within this pod.

Why are orcas doing this? Is it revenge?

Online rumours have swirled about an orca called White Gladis, who was supposedly traumatised in an encounter with a boat. This is speculation based on healed injuries on her fins, but it isn’t clear that those injuries were caused by an encounter with a boat. Orcas rake each other with their teeth, which could offer another explanation for the scars. Most experts agree there isn’t any evidence that White Gladis is training other whales to attack, and there is no clear motive for podmates to risk personal injury for her vengeance. It is also unknown if White Gladis was involved in this latest clash.

“Nobody knows why this is happening,” says Trites. “All the reports coming in have been from non-scientists, non-specialists – people that are terrified.” He says orcas are a highly intelligent species capable of self-recognition, but that doesn’t necessarily mean they are capable of planning and enacting revenge.

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What else could be behind the increase in orca encounters?

Both Trites and Giles think it is more likely that the orcas are just having fun or seeking an admittedly terrifying back scratch. “These whales are very tactile,” says Giles. “They interact with things in their environment, including each other.” A pod of whales in British Columbia has been seen vigorously rubbing against rocky beaches, for example.

Wild orcas have never been documented hunting or eating humans, so it is unlikely this relates to wanting a meal.

Until researchers know what is motivating the encounters, it will be challenging to abate them. If the orcas see the activity as a game, for example, fleeing may elicit a more aggressive response. “This is something that we humans need to figure out and not place the blame on the whales,” says Giles.