The vast majority of whales are filter feeders that consume tiny organisms like plankton and krill. This predatory relationship with seals is therefore not a general characteristic of the whale family. The consumption of seals is instead limited to a highly specialized, carnivorous subset of the toothed whale group, representing a distinct ecological niche among ocean predators. This relationship is driven by learned behavior and a preference for high-energy prey.
Identifying the Marine Mammal Hunters
The only animal commonly referred to as a whale that consistently preys on seals is the killer whale, Orcinus orca. Scientists recognize distinct populations called ecotypes that specialize in different diets and exhibit unique behaviors. The distinction between these ecotypes is important, as not all killer whales are mammal hunters.
The population responsible for consuming seals is known as the Transient, or Bigg’s, killer whale, which ranges along the coastlines of the North Pacific and other global regions. These transients are genetically and culturally separate from the “Resident” killer whales, which inhabit the same waters but feed exclusively on fish, especially salmon. Transient killer whales possess a different morphology and social structure, evolving to pursue warm-blooded prey. They often travel in smaller pods of two to six individuals, relying on stealth to surprise their acoustically sensitive prey.
Specialized Hunting Tactics
The successful predation of seals requires sophisticated, cooperative hunting strategies that capitalize on the intelligence and power of the pod. Transient killer whales often hunt with near-total silence, minimizing their vocalizations to avoid alerting seals and sea lions, which possess excellent underwater hearing. This stealth allows them to approach haul-out sites or resting seals without detection, making surprise a major component of a successful attack.
One of the most dramatic coordinated tactics is “wave washing,” primarily observed in Type B killer whales in the Antarctic. When a seal is spotted resting on an ice floe, the pod will line up shoulder-to-shoulder and swim in synchronized, powerful bursts toward the ice. This collective movement creates a large, deliberate wave that washes over the floe, effectively knocking the seal into the water where other pod members are waiting. Young whales are often observed practicing this technique, indicating that it is a learned cultural behavior passed down through generations.
In areas without ice floes, such as the gravel beaches of the Valdes Peninsula in Argentina, a different specialized tactic is employed: intentional stranding. Certain killer whale pods will use the momentum of a breaking wave to propel themselves partially onto the shore. They briefly slide onto the beach to snatch unsuspecting seals or sea lion pups before wriggling back into the water with their catch. This extremely risky maneuver, which can be fatal if misjudged, is a testament to the high degree of specialization and the cultural transmission of complex hunting skills.
The Role of Seals in the Hunter’s Diet
For the Transient ecotype, seals and sea lions represent a significant, high-calorie food source, making up a large percentage of their observed diet. Specifically, harbor seals are a primary prey item for Transients in the North Pacific, constituting more than half of their recorded diet in some regions. The blubber layer of pinnipeds provides a dense, energy-rich meal that is beneficial for sustaining the large body mass of a killer whale.
While seals are a dietary staple, they are not the exclusive food source for Transient killer whales, which also consume porpoises, dolphins, and the calves of larger whales. The consumption of seals can vary regionally and seasonally, often increasing when seal populations are abundant or during pupping seasons. The recent increase in Transient sightings in the Salish Sea, for example, is strongly correlated with a rebound in the local harbor seal and sea lion populations, illustrating the direct link between predator presence and prey availability.