For more than five years, a small population of killer whales in the waters off Spain and Portugal has been colliding with sailboats, nudging and biting their rudders and, in a handful of cases, damaging vessels badly enough to sink them. Marine biologists have logged hundreds of these encounters since 2020, yet despite intense study they have not settled on a firm explanation for why the animals started, making the behavior one of the more genuinely puzzling wildlife stories in recent memory.
A pattern that began in 2020
The first reports emerged in the spring of 2020 near the Strait of Gibraltar, where sailors described orcas approaching from behind, striking the rudder, and sometimes spinning a boat in circles before losing interest. What might have looked like isolated incidents quickly became a recognizable pattern, concentrated along the Atlantic coasts of the Iberian Peninsula and the strait that separates Europe from Africa.
Researchers tracking the events have documented well over 700 interactions in the years since, ranging from gentle contact to forceful ramming. A small number of boats have gone down after the whales disabled their steering and cracked their hulls, with at least six vessels sinking, though in most encounters crews escaped unharmed and no human has been killed.
The critically endangered whales involved
The animals behind the interactions belong to a distinct subpopulation of Iberian killer whales that numbers only a few dozen individuals, a group considered critically endangered. Because the population is so small, scientists have been able to identify particular whales, many of them juveniles, that appear again and again in the reports. That intimacy of data is unusual and has helped researchers rule out some explanations while deepening the mystery of others.
Federal marine science agencies such as the National Oceanic and Atmospheric Administration’s fisheries service describe orcas generally as highly social, intelligent predators that learn behaviors from one another and pass them through a pod, a trait that helps explain how an unusual habit could spread among a tight-knit group even if it cannot say why the habit began.
Competing theories about the cause
Several hypotheses have circulated among scientists, none of them proven. One leading idea holds that the behavior is a form of play or a passing fad, a self-reinforcing game that juveniles find stimulating and imitate, much as captive and wild orcas have adopted temporary trends like wearing dead salmon on their heads. Under this reading, the rudders offer an appealing target because they move, resist and provide tactile feedback when pushed.
A competing and darker explanation suggests the interactions could trace back to a stressful or traumatic encounter, perhaps a collision or entanglement involving a particular female, that prompted a defensive or agitated response later copied by others. Reporting compiled by outlets including Mongabay has noted that researchers increasingly lean toward the playful-fad interpretation, in part because the whales do not appear to treat boats as prey or threats, but the trauma theory has not been fully dismissed.
How the numbers have shifted
The frequency of encounters has not held steady. After climbing through the early years, reported interactions along the Iberian Atlantic coast dipped in 2024 compared with the previous year, only for clusters of activity to flare again in specific areas and seasons. That variability complicates any simple narrative of a behavior that is either fading or escalating, and it keeps authorities from declaring the phenomenon over.
Seasonal movement of the whales, which follow migrating bluefin tuna, means the encounters concentrate in particular months and stretches of coastline, allowing officials to issue localized warnings when the animals are known to be present.
What sailors are told to do
Guidance issued to boaters reflects the uncertainty. Rather than fighting back, crews are generally advised to slow down or stop the vessel, lower the sails, and let go of the wheel so the rudder stops moving, on the theory that a stationary, unresponsive boat is less interesting to a whale looking for a reaction. Mariners are also urged to report every encounter, feeding the databases that scientists rely on to track individuals and map hot spots.
Conservationists stress an additional point amid the alarming imagery: the whales are a fragile, protected population, and the priority is to avoid harming them even as the interactions damage boats. Retaliation, they warn, could push an already endangered group closer to collapse, and some sailors have been cautioned against firing flares, revving engines aggressively or striking the animals in ways that might injure them or provoke a stronger response.
Scientists tracking the behavior emphasize how unusual it is to watch a novel habit emerge and spread in real time within a wild population, a situation that offers a rare window into orca culture and learning. For now the episodes continue, a rare case in which one of the ocean’s most studied predators is doing something its human observers can describe in detail but cannot yet fully explain, and the mystery endures as researchers keep logging every push, bite and sinking in the hope that the pattern will eventually give up its cause.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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