Killer whales, also known as orcas, are the ocean’s apex predators, known for their high intelligence and sophisticated social structures. They live in complex family groups and exhibit a remarkable capacity for learning and cultural transmission. Recently, a highly unusual and coordinated behavior involving interactions with boats has captured global attention. This phenomenon, first documented in 2020, involves orcas repeatedly approaching and damaging vessels, forcing researchers to investigate the motivations behind this conduct.
The Geography and Nature of the Boat Interactions
The unusual behavior is focused on the waters off the Iberian Peninsula, specifically along the coasts of Spain and Portugal, including the Strait of Gibraltar. Since the first documented incident in May 2020, hundreds of interactions have been recorded, with the number increasing year-over-year. The behavior is not characterized by random acts of aggression but is highly focused on specific targets.
The orcas primarily target medium-sized sailboats, usually vessels under 50 feet in length. The animals repeatedly bump and push against the boat, concentrating their efforts almost exclusively on the rudder. This sustained focus often results in the rudder being damaged, broken, or torn off, leaving the boat disabled and requiring rescue. Although frightening for mariners, experts note the behavior does not appear to be an intentional “attack” aimed at harming humans, as the orcas tend to leave once the vessel is immobilized.
The Specific Iberian Orca Subpopulation
The orcas involved in these incidents belong to the distinct and vulnerable Iberian orca subpopulation. This population is genetically isolated and feeds primarily on Atlantic bluefin tuna migrating through the Strait of Gibraltar. The International Union for Conservation of Nature (IUCN) classifies this subpopulation as Critically Endangered, with potentially fewer than 40 individuals remaining.
The disruptive behavior is confined to a specific group within this population, with at least 15 individuals identified as participants or observers. Many of the most active individuals are juveniles, which is a significant factor in understanding the behavior’s cause. Orcas possess a high degree of social learning; a novel behavior developed by one individual can quickly spread and become a temporary cultural tradition within the pod. The behavior is thought to have been initiated by a few specific individuals, sometimes referred to as the “Gladis” orcas, and transmitted through the family unit.
Leading Theories Explaining the Behavior
The Play or Social Fad Hypothesis
One widely accepted explanation is that the boat interactions are a temporary social fad or a form of coordinated play. Orcas are highly intelligent and have a documented history of developing non-adaptive, temporary cultural trends that spread through social learning. For instance, one group of orcas temporarily began wearing dead salmon on their heads, a behavior that quickly disappeared.
This theory suggests that young, curious orcas began interacting with rudders as a form of play or exploration. The focus on the rudder may be an evolution of a known behavior where orcas swim into a vessel’s propeller wash. The rudder’s movement and resistance may offer an engaging physical challenge or be stimulating due to sound or vibration. Since many participants are juveniles, scientists believe the behavior may be a temporary phase that has become popular within their peer group.
The Trauma/Defensive Behavior Hypothesis
Another hypothesis suggests the behavior originated from a traumatic or “aversive” incident experienced by one of the lead individuals. This theory often centers on an adult female, ‘White Gladis,’ who may have suffered a painful collision with a boat or become entangled in fishing gear. Scars consistent with vessel strikes or fishing gear have been observed on approximately three percent of the Iberian orca population.
The initial interaction may have been a defensive or retaliatory response to a perceived threat, specifically targeting the rudder as the source of the danger. Because orcas are highly social, this defensive action was quickly imitated and learned by other members of the pod, particularly the juveniles. This spread makes the behavior look like a coordinated effort, teaching the group that rudders are objects to be neutralized.
The Resource Competition/Stress Hypothesis
A less prominent theory connects the behavior to environmental pressures within the region. The Iberian orcas rely heavily on Atlantic bluefin tuna, a species whose stocks have been severely impacted by commercial fishing. Scientists propose that the orcas may associate boats with competition for their primary food source, which could cause a stress response.
The stress caused by scarcity, combined with sensory overload from shipping traffic and noise pollution in the Strait of Gibraltar, could manifest as unusual behavioral patterns. While stress alone is unlikely to explain the specific interaction with rudders, it provides context for why this highly intelligent predator might exhibit an atypical response to human activity. Researchers emphasize that these are currently hypotheses, and no single explanation has been definitively confirmed.