Orcas, also known as killer whales (Orcinus orca), are documented predators of sharks, including the largest species in the ocean. This behavior confirms the orca’s position as the apex predator in all global marine environments. While sharks are formidable predators, they have a single known natural enemy, and the interactions between the two species are highly specialized. The predatory technique employed by orcas against large sharks is a testament to their advanced social learning and strategic thinking.
The Specialized Hunting Technique
The successful hunting of large, powerful sharks, such as the Great White, requires a coordinated effort from a pod of orcas. The technique is not a random attack but a series of calculated maneuvers designed to quickly incapacitate the prey. The initial stages of the hunt often involve the orcas ramming the shark’s side with their bodies or delivering powerful tail slaps to disorient it.
The most crucial step in the process is inducing a state known as tonic immobility, which is a temporary, trance-like paralysis. Orcas achieve this by flipping the shark completely upside down, a position that alters the shark’s sensory perception. Once the shark is inverted and defenseless, the orcas can approach with minimal risk of injury.
The pod then executes a precise procedure to access the shark’s liver. Necropsies on shark carcasses washed ashore show a clean tear or opening in the pectoral girdle area, located between the pectoral fins. This wound allows the orcas to extract the liver while leaving the rest of the carcass largely intact and uneaten. The precision of the extraction, which minimizes damage to the surrounding tissue, demonstrates a high level of learned skill within the pod.
The Nutritional Motivation
The reason for the orcas’ selective targeting of the liver is energy and nutrient density. Shark livers serve as massive storage organs, often constituting up to one-third of the shark’s total body weight. This organ is rich in lipids and fat-soluble vitamins, providing a caloric reward that justifies the effort and risk of the hunt.
The high energy content is due to the liver’s composition, which can be over 50% fat by wet mass in species like the Great White shark. This fat includes squalene, a highly unsaturated triterpenoid hydrocarbon. Squalene is a low-density lipid that sharks use for buoyancy control, and it is a massive store of energy for the orca.
For transient orcas that cover vast distances, this single organ provides a concentrated calorie boost not available in other parts of the shark’s body. Consuming the entire carcass, which is mostly muscle and cartilage, would be significantly less efficient for the energy expended. The specialized technique is a learned strategy to maximize caloric intake while minimizing hunting time and risk.
Specific Shark Species Targeted
The hunting of sharks is a behavior observed in specific ecotypes of orcas, particularly transient and offshore populations whose diets include marine mammals and various fish species. The most frequent victims of this predatory specialization are the Great White shark (Carcharodon carcharias) and the Broadnose Sevengill shark (Notorynchus cepedianus). Documented cases off the coast of South Africa, involving a pair of orcas known as Port and Starboard, have shown a dramatic impact on local Great White and Sevengill populations.
These two orcas have been linked to the mass killing of up to 19 sevengill sharks in a single day, with all carcasses found missing their livers. In other regions, such as the Gulf of California and New Zealand waters, orcas have also been observed preying on other species, including juvenile Great Whites and Shortfin Mako sharks (Isurus oxyrinchus). These observations confirm that the behavior is not exclusive to a single location or shark species.
The localized nature of the attacks suggests that the specialized hunting method is a culturally transmitted trait, passed down through generations within certain pods. When orcas arrive and begin hunting in a new area, the local shark populations, particularly Great Whites, will often flee their traditional aggregation sites for extended periods. This mass displacement demonstrates a learned avoidance response to the presence of these highly effective marine predators.