Orcas, also known as killer whales, are marine mammals. Their diet is remarkably diverse, showcasing their adaptability as predators across various marine environments. Their diet varies globally, reflecting specialized populations and local food availability. This dietary flexibility allows different orca groups to thrive in distinct ecological niches around the world.
General Characteristics of Orca Diet
Orcas are apex predators. Globally, their diet encompasses over 140 different animal species. This broad range includes various types of fish, cephalopods like squid, marine mammals such as seals and other whales, and even seabirds and sea turtles. However, individual orca populations often display specialized feeding habits, focusing on particular prey items available in their specific habitats.
Specialized Diets of Orca Ecotypes
The diet of orcas varies significantly among distinct populations, known as ecotypes, which have evolved unique prey preferences and hunting strategies. Resident orcas, primarily found in the North Pacific, are fish-eaters, with salmon constituting a substantial portion of their diet. Chinook salmon is a preferred food source due to its large size, high fat content, and year-round availability, making up about 65% of the salmon they consume. They also eat chum and coho salmon, but not smaller species like sockeye or pink salmon, and rarely marine mammals.
In contrast, Transient orcas, also known as Bigg’s orcas, are specialized marine mammal hunters. Their diet includes seals, sea lions, porpoises, dolphins, and even larger whales like minke whales and gray whale calves. These orcas employ stealthy hunting techniques and often remain silent to avoid detection by their acoustically sensitive prey. Transient orcas rarely, if ever, consume fish.
Offshore orcas, a lesser-known ecotype, primarily feed on sharks and other fish species. Research indicates that sharks, such as Pacific sleeper sharks, blue sharks, dogfish, and salmon sharks, account for over 90% of their observed diet. Offshore orcas often target the fatty liver of sharks, and the abrasive skin of their prey leads to significant wear on their teeth.
Hunting Techniques and Prey Capture
Orcas exhibit diverse and sophisticated hunting techniques, often working cooperatively within their pods to capture prey. Cooperative hunting involves groups herding fish into dense “bait balls” before taking turns stunning them with powerful tail slaps, a method observed in populations like those off Norway. For marine mammals, pods may work together to exhaust or separate individuals from their groups.
Some orca populations employ unique strategies such as wave washing, where they create large waves to dislodge seals or penguins from ice floes, making them vulnerable. Another specialized technique is strand feeding, where orcas temporarily beach themselves to catch seals or sea lions on shore, a behavior requiring precise timing and coordination. For larger prey, orcas may use ramming or stunning tactics, utilizing their immense body mass to incapacitate their target.
Geographic and Seasonal Variations in Diet
Beyond the specialization of ecotypes, the diet of orcas is also influenced by their geographic location and seasonal availability of prey. In Arctic regions, for instance, orcas may hunt beluga whales and narwhals, reflecting the dominant prey species in those cold waters. Conversely, orcas in temperate zones, such as the North Pacific, heavily rely on migratory salmon runs during specific seasons.
Seasonal changes can trigger shifts in feeding patterns as orcas follow the movements of their primary food sources. The timing of salmon migrations or the pupping seasons of seals can dictate the movements and dietary focus of local orca populations. Orcas off New Zealand, for example, have been observed to primarily prey on rays and sharks, showcasing how regional prey abundance shapes their feeding habits.