The orca, or killer whale, is the ocean’s most widely distributed predator, occupying the top spot in marine food chains across every ocean basin. These highly intelligent animals are found from the polar ice edges to the warm waters of the equator, demonstrating a remarkable ability to adapt to diverse environments. Orca feeding habits are highly specialized and differ greatly between various populations. This complex feeding behavior is defined by distinct cultural and geographic preferences that dictate exactly what they consume.
The Foundation of Orca Diet Specialization
Differences in feeding habits among orcas stem from the existence of distinct, non-interbreeding populations known as ecotypes. These ecotypes have evolved specialized diets, hunting techniques, and social structures, even when their ranges overlap. In the North Pacific, three primary ecotypes are recognized: Residents, Transients (also called Bigg’s orcas), and Offshores. A strict dietary line exists between these groups. Fish-eating orcas, such as the Residents, never consume marine mammals, and mammal-eating orcas entirely ignore fish. This cultural boundary means an orca’s diet is determined by the family group it is born into and the traditions passed down. This specialization has even led to physical differences, such as fish-eaters possessing smaller, less robust teeth than their mammal-hunting relatives.
Diet of Marine Mammal Specialists
The diet of Transient, or Bigg’s, killer whales focuses exclusively on warm-blooded marine animals, making them the ocean’s premier marine mammal hunters. Transients travel in smaller, quieter groups than their fish-eating counterparts, an adaptation necessary for stealthily approaching intelligent and aware prey. Their hunting requires precision and coordination to subdue large or fast-moving targets.
Their prey includes:
- Harbor seals
- Steller sea lions
- Harbor porpoises
- Various species of dolphins
Mammal specialists also target larger whale species, particularly the calves of migrating gray whales and humpback whales. Orcas work together to separate a calf from its protective mother, a prolonged and dangerous process that demonstrates their cooperative intelligence. In the Antarctic, specific ecotypes, like Type B orcas, primarily hunt seals, while Type A orcas focus on larger prey like Antarctic minke whales. The high caloric value of marine mammal blubber provides the energy density required to sustain their large bodies. This reliance on fatty prey means mammal-eating orcas often accumulate high levels of environmental contaminants, as toxins bioaccumulate up the food chain.
Diet of Fish Specialists
Fish specialists are best represented by the Resident killer whales of the North Pacific, whose feeding habits are highly specialized and culturally ingrained. For the Southern Resident population, the diet is dominated by Chinook salmon, comprising up to 96% of their total intake during summer months. Orcas prefer Chinook because it is the largest and most energy-rich Pacific salmon species, possessing the highest fat content necessary for the whales’ survival.
When Chinook salmon are less abundant, the Residents must broaden their diet, though they still primarily consume other fish species. Secondary prey items include:
- Chum and coho salmon
- Pacific halibut
- Lingcod
- Steelhead trout
In the North Atlantic, other fish-eating populations specialize in schooling fish, such as Norwegian spring-spawning herring and mackerel. These fish are pursued during massive seasonal migrations, requiring the orcas to follow their movements across vast distances. The less-studied Offshore ecotype primarily eats fish, with a preference for sharks and rays, often targeting the highly nutritious liver.
Acquisition: Cooperative Hunting Techniques
The capture of prey, whether fish or mammal, relies on sophisticated, culturally transmitted cooperative hunting strategies. One dramatic method is “carousel feeding,” used in the North Atlantic to hunt schooling fish like herring. This technique involves a group isolating a section of the school and herding the fish into a dense “bait ball” near the surface. The whales then take turns stunning the fish by slapping the ball with their powerful tails, consuming the incapacitated prey.
Against marine mammals, specialized techniques require precise teamwork and environmental manipulation. Antarctic orcas hunt seals resting on ice floes using “wave-washing.” This involves synchronized underwater charges that create a massive wave, washing the seal off the ice and into the water. Mammal-eating orcas have also been documented intentionally stranding themselves briefly on shorelines to snatch pinnipeds resting on the beach. The coordinated separation of large whale calves from their mothers requires a sustained effort where pod members take turns wearing down the parent.