Orcas are marine apex predators found in every ocean worldwide. Despite their common name “killer whale,” their diet is not uniform across all populations. What they eat varies significantly based on their specialized lifestyles and the prey available in their specific habitats.
Diverse Diets of Orca Populations
Orcas comprise distinct populations, often called ecotypes, each with a highly specialized diet and unique foraging strategies. Worldwide, over 140 animal species, including bony fish, sharks, rays, and 50 marine mammal species, have been observed as prey for killer whales.
Resident orcas, primarily found in the North Pacific, mainly consume fish, with a strong preference for salmon. Southern Resident killer whales, for instance, specialize in Chinook salmon, which can constitute up to 80% of their diet. Other salmon species like chum and coho are also consumed, especially when Chinook is less available. Alaskan Resident orcas may exhibit a more varied fish diet, including sablefish, flounder, lingcod, and halibut, supplementing their salmon intake.
Transient orcas, also known as Bigg’s killer whales, exclusively hunt marine mammals. Their diet includes seals, sea lions, porpoises, dolphins, and even larger whales such as minke whales or gray whale calves. These mammal-eating orcas employ stealthy hunting techniques and typically do not use echolocation to locate their prey, as marine mammals have acute hearing. They are found along the Pacific Coast, from Alaska to California.
Offshore orcas, inhabiting deeper waters, often include sharks and large schooling fish in their diet. They consume sharks like Pacific sleeper sharks, and the rough skin of these prey can lead to significant tooth wear. The fatty livers of sharks, which can account for a large percentage of their body weight, are a particularly sought-after part of the prey.
In Antarctic waters, different orca types exhibit unique dietary specializations. Type A orcas primarily prey on Antarctic minke whales and occasionally hunt southern elephant seals. Large Type B whales mainly consume seals, particularly Weddell seals, and also hunt minke whales. Small Type B killer whales have been observed hunting penguins and are believed to primarily eat fish, while Type C orcas specialize in Antarctic toothfish.
Hunting Strategies and Social Behavior
Orcas employ sophisticated hunting methods adapted to their specific diets, often involving complex social cooperation within their pods. These techniques are learned and passed down through generations.
In regions like Norway, some orcas use “carousel feeding” to herd schooling fish, such as herring, into a dense ball near the surface. They then slap the ball with their tail flukes, stunning or killing the fish before consuming them.
Antarctic orcas use “wave-washing” to hunt seals resting on ice floes. A group of orcas swims in synchrony, creating a powerful wave that washes the seal off the ice and into the water, where they can capture it. This often involves initial “spy-hopping” to locate prey. The whales strategically break up larger floes or create waves to dislodge seals.
Another specialized hunting method is “beach-stranding,” observed in populations like those in Argentina’s Valdes Peninsula and the Crozet Islands. Orcas deliberately beach themselves to snatch sea lions or seal pups from the shore. This high-risk behavior is often taught by experienced adults to younger whales. Bigg’s killer whales in the Salish Sea have also been observed attempting this tactic.
For larger prey, such as other whale species, orcas engage in prolonged pursuit and strategic attacks. They may take turns ramming, biting, and pulling on the prey, working to wear it down. Some populations have developed techniques to drown larger whales by forcing their blowholes underwater for extended periods.
Diet’s Influence on Orca Life
An orca’s specific diet profoundly influences its biology and behavior, shaping social dynamics and movements. Dietary specialization dictates the social structure of orca pods.
Resident orcas, with their abundant fish diet, typically form larger, more stable matrilineal groups. In contrast, Transient orcas, which hunt mobile marine mammals, tend to live in smaller, more fluid groups, often consisting of a female and her offspring. This difference reflects the varying demands of their hunting strategies.
Migration patterns and seasonal distributions of orcas are directly linked to the availability and movement of their preferred prey. Resident orcas, for example, follow seasonal salmon runs to areas where food is abundant. A decline in specific prey populations, such as Chinook salmon for Southern Residents, can significantly impact an orca population’s health and survival, leading to nutritional stress.
Physical adaptations can reflect an orca’s long-term dietary specialization. Offshore orcas, known for consuming sharks, often exhibit worn teeth due to the abrasive nature of shark skin. This dental wear is a direct consequence of their unique diet.
As apex predators, orcas play a significant role in shaping marine food webs by influencing prey populations. For instance, mammal-eating transients can impact pinniped and sea otter populations. The specialized diets of different orca ecotypes mean their ecosystem impact is not uniform, but a mosaic of predator-prey relationships.