The Orca's strength and cooperative hunting ability enable it to eat anything in the ocean, from the smallest fish to the largest baleen whales, such as gray and even blue whales. Resident orcas feed exclusively on fish, preferring salmon, but also feed on halibut, hake and other fish species. In captivity they will eat over 100 pounds in a day. When foraging, residents spread out to form a broad front along coastal waterways. After locating fish they will alert other pod members, slap their flukes and flippers to herd the fish and drive them into the path of other whales.
Transients roam widely in small groups and are often observed entering small bays and channels to locate seals, sea lions or porpoises. Transients hunt silently using passive sonar and often dive for ten to fifteen minutes to sneak up and attack their prey. Tail flukes are often used to stun prey, which is then drowned. Unlike residents, transients will often share food among members, and they will vocalize most profusely at this time.
Transients reject fish as a food source, and in captivity will often starve rather than accept this diet. These whales specialize in hunting marine mammals and will also harass and eat sea birds, and attack deer and moose that swim across narrow marine passages. In Punte Norte, Argentina, transients have learned to beach themselves in order to prey on young sea lions.
Attacks on larger marine mammals, such as baleen whales, are even more dramatic. An account of an attack on a young blue whale in Baja, during which huge chunks of flesh were stripped and eaten by a group of transients over five hours, underscores their collaborative power. Gray whales have been seen to roll on their backs with fear rather than escaping or fighting a transient whale attack.
Eyewitnesses in Alaska reported seeing two transients work together to tip an ice floe and slide a sleeping seal into the mouth of a third orca. Transients also have a substantial appetite. One 19th century zoologist found the remains of thirteen porpoises and fourteen seals in the stomach of a transient and another lodged in its throat. More recently a beached orca on Vancouver Island was found with several intact Dall's porpoises in its stomach.
Such accounts have been responsible for human fear and hatred of orcas, and even its common name, killer whale. However, transients do not kill indiscriminately and have never been known to attack and eat humans. Nonetheless, researchers warn people not to swim near transients, since in 1972 a surfer was bitten and released by an orca.
