Recent Orca Attacks on Boats

The subpopulation of killer whales (Orcinus orca) inhabiting the Strait of Gibraltar primarily feeds on Atlantic bluefin tuna (Thunnus thynnus). These whales are typically observed in the strait during spring and summer when they forage for tuna. A census conducted in 2011 recorded only 39 individuals in this subpopulation. Because of its small size and declining prospects, the Spanish government established a conservation plan in 2017, and the International Union for Conservation of Nature (IUCN) classified the group as critically endangered. Despite these protections, many mitigation measures have had limited success, and the whales continue to live in an environment strongly influenced by human activity, including fishing pressure, reduced prey availability, and heavy maritime traffic.

（Courtesy of Jean-Christophe Guillaumin）

Beginning in May 2020, a series of unusual incidents was reported along the coasts of Spain and Portugal. Killer whales were repeatedly approaching vessels—especially sailing boats—and interacting with them in ways that often resulted in damage. Individuals struck the hull, bit or broke rudders, and in some cases disabled steering systems entirely. Such behavior had rarely been documented on a broad scale before, and the sudden increase in events surprised marine mammal researchers, who quickly formed an international working group to investigate the phenomenon.

Most incidents involved monohull sailing boats approximately 12 meters in length, particularly those equipped with spade rudders. This type of rudder is attached only at the upper end of the rudder shaft and therefore lacks structural support along its lower portion, making it comparatively fragile. In several cases, killer whales struck or twisted the rudder until it fractured, split, or bent the rudder shaft, leaving the vessel unable to steer and requiring towing back to port. By contrast, inflatable boats, motorboats, and catamarans were rarely targeted. This pattern suggests that the whales may show a preference for specific vessel designs, possibly reflecting accumulated experience or learned recognition of particular structures.

The behavior was not limited to isolated individuals. Observations in 2020 documented at least 31 identifiable killer whales, of which nine actively interacted with vessels. These individuals formed two social groups, each with recognizable members identified through photo-identification techniques. The first group consisted mainly of juveniles—Gladis Negra, Gladis Peque, and Gladis Gris—while their mother, Gladis Herbille, was occasionally present but tended to remain farther from the boats. The second group included Gladis Blanca and her offspring Gladis Filabres, accompanied by relatives Gladis Clara and Gladis Dalila. In this group, their matriarch Gladis Lamari was sometimes observed nearby but generally avoided direct involvement. In both groups, younger whales were the primary participants in the disruptive interactions.

The encounters typically unfolded through a series of stages. First, the whales approached stealthily from the stern of a moving vessel, often unnoticed by the crew. Next, they positioned themselves beneath the boat and began exploring it, touching the hull or rudder while sometimes rolling sideways or exposing their ventral surface. In the third stage, attention focused on the rudder. Whales pushed it with their heads or used their bodies as levers, causing the rudder to rotate and occasionally forcing the vessel into tight circles approaching a full rotation. If the rudder broke or steering control failed, the boat slowed or stopped. Finally, once the vessel lost maneuverability or the engine was shut down, the whales gradually lost interest and departed. Some individuals were also observed tail-slapping or creating bubbles, giving the encounters an appearance reminiscent of playful behavior.

The reason for this unusual activity remains uncertain. One possibility is that a previous negative encounter—such as a collision with a boat—triggered a learned avoidance or retaliatory response. Another explanation links the behavior to chronic human pressures affecting the population, including competition with fisheries and declining prey resources. A third hypothesis considers the role of curiosity and social learning. Killer whales possess remarkable cognitive abilities and are known to transmit behaviors culturally within their social groups. It is therefore possible that the initial interactions began as exploratory or playful actions and subsequently spread through imitation among younger individuals.

During 2020, researchers compiled 119 opportunistic records of killer whale sightings along the Iberian Peninsula, including 49 confirmed vessel interactions. Most occurred between July and October as the whales moved northward from the Strait of Gibraltar toward the coast of Galicia in northern Spain, with some later returning southward toward Portugal. These animals were generally observed near the continental shelf and tended to travel closer to shore when moving north.

Authorities responded by introducing precautionary measures. Radio alerts were issued warning sailors about whale activity, and Spain temporarily restricted navigation by small sailing vessels in areas where interactions were concentrated. Media coverage and widely shared videos of the incidents—often accompanied by the alarm of onboard crews—further heightened public awareness.

From a social perspective, the behavior also reveals interesting dynamics within the whale groups. In several cases, adult females appeared to remain at a distance while younger whales engaged directly with the vessels, suggesting a form of tolerated experimentation or exploratory learning within the pod. One individual, Gladis Negra, was observed with a head injury of unknown origin, possibly resulting from a collision or a previous interaction with a vessel.

These encounters between humans and killer whales are still ongoing. Similar incidents continued to occur as recently as April 2025 along the coast of Cádiz, Spain. If the behavior spreads further within the population, it could present an increasing challenge both for maritime safety and for conservation. Any escalation of conflict might provoke defensive responses from sailors or accidental harm to the whales themselves, placing an already vulnerable subpopulation under additional pressure. The situation raises difficult questions: whether vessels should attempt to avoid or deter the animals, how to minimize risks to both whales and sailors, and whether a sustainable path toward coexistence can be found in one of the world's busiest maritime corridors.

Related video:

https://www.youtube.com/watch?v=E1rqcI2jULY

Author: Shui-Ye You

Reference:

Esteban R et al. (2020). Killer whales of the Strait of Gibraltar, an endangered subpopulation showing a disruptive behavior. Marine Mammal Science.