Orcas, also known as killer whales, are the largest members of the dolphin family and apex predators in marine environments. Given their shared habitat, a common question is whether orcas prey on dolphins. This article explores the relationship between these two marine species.
Orca Predation on Dolphins
Orcas prey on dolphins, though the frequency varies significantly by population and location. While orcas have a diverse diet, ranging from fish to other marine mammals, dolphins are a common part of the diet in some areas, while rare in others. For instance, a group of orcas off the coast of Chile was recently observed hunting and consuming dusky dolphins, a behavior not previously documented for orcas in that region.
Understanding Orca Ecotypes
Not all orcas exhibit the same dietary preferences, a distinction explained by “ecotypes.” Ecotypes are populations that have evolved distinct differences in diet, behavior, and even physical appearance, despite sharing the same species name. The three primary ecotypes found in the North Pacific are Resident, Transient (also known as Bigg’s), and Offshore orcas.
Resident Orcas
Resident orcas primarily consume fish, with a strong preference for salmon, particularly Chinook salmon. They live in stable, complex family groups and are highly vocal, using echolocation to find their fish prey.
Transient (Bigg’s) Orcas
Transient orcas are marine mammal specialists, with their diet consisting almost exclusively of seals, sea lions, porpoises, and other whale species, including dolphins. They typically hunt in smaller, stealthier groups and are much less vocal than Residents, as their prey has acute hearing.
Offshore Orcas
Offshore orcas, a less understood ecotype, primarily inhabit open waters and are known to feed on schooling fish and sharks, such as sleeper sharks. Their teeth show significant wear, likely due to consuming the tough skin of sharks. Therefore, it is predominantly the Transient (Bigg’s) ecotype that hunts dolphins.
Why Orcas Target Dolphins
The primary motivation for Transient orcas to target dolphins is sustenance. Dolphins represent a nutritious food source for these marine mammal-eating ecotypes. This predator-prey relationship has influenced the behaviors and adaptations of both species.
Orcas also engage in hunting to teach younger pod members essential survival skills. Adult orcas have been observed instructing calves in hunting techniques, sometimes allowing weakened prey to escape so young orcas can practice capturing them. Additionally, orcas may engage in opportunistic feeding when dolphins are vulnerable. Some scientists suggest orcas might also harass dolphins to deter them from shared hunting grounds.
Hunting Strategies and Methods
When hunting dolphins, orcas employ sophisticated and coordinated strategies. They often work as a team, much like wolf packs, to isolate an individual dolphin from its pod. Once targeted, orcas may engage in high-speed chases, often leaping out of the water. The hunt can be prolonged, lasting 15 to 25 minutes, as they wear down the dolphin’s stamina.
Orcas utilize their immense power to subdue their prey. They may ram dolphins with their bodies, inflicting significant internal injuries. Other tactics include grasping the dolphin crosswise in their mouths and dragging it beneath the surface, or using their powerful tails to stun or kill prey by slapping them. Observations have documented orcas throwing dolphins into the air, a behavior that can disorient and injure the prey. After a successful hunt, orcas often share the spoils with other pod members, including calves.