Orcinus orca

Description and Fascinating Facts

13-year-old T2C2 (Tumbo) has severe scoliosis, an extremely rare deformity of the spine, which affects his ability to swim and hunt. His family wait for him to catch up and provide food for him.

The orca, also known as the killer whale, is actually a dolphin. It is the largest of the dolphin family (Family Delphinidae: 32 species, including the dolphins, pygmy killer whales (Feresa attenuata) and false killer whales (Pseudorca crassiddens). Orcas reach a maximum length of over 9 m (30 ft) and can weigh 7,257 kg (16,000 lbs).

Because of their fierce reputation, orcas are sometimes called the ballena asesina or “assassin whale” by the Spanish. They were referred to as “whale killers” by sailors who witnessed their attacks on larger cetaceans, and over time this name was changed to “killer whales.” They are called this not because they harm humans but because they do sometimes kill other whales, hunting them in packs thereby earning the title “wolves of the sea”. Orcinus is probably derived from Orcus, an ancient mythological Roman god of the netherworld – a reference to the ferocious reputation of this animal. Orca literally means “the shape of a barrel or cask” in Latin, likely due to the killer whale’s body shape. Orcas are usually seen travelling in pods of between 3–45 individuals, usually including at least one large male.

World Range and Habitat

Next to humans, orcas are the most widely distributed mammal. Orcas inhabit all oceans of the world but are most numerous in the Arctic, the Antarctic and areas in nutrient-rich cold-water upwellings such as the Pacific Northwest. They have been sighted along the shores of Washington, Oregon, California, Baja California, and along the eastern coast of the United States. In addition to cold water areas, orca also have been seen in warm water areas such as Hawaii, Australia, the Galapagos Islands, the Bahamas, and the Gulf of Mexico. Such sightings are infrequent, but they do demonstrate the orcas ability to venture into tropical waters. Even more surprising, orcas have been seen in fresh water rivers around the world such as the Rhine, the Thames, and the Elbe. One orca was reported to have even travelled some 177 km (110 miles) up the Columbia River in search of fish. Although orca can be found in both the open ocean and coastal waters, they primarily inhabit the continental shelf in waters less than 200 m (660 ft) deep. In cold water areas, their distribution is limited by seasonal pack ice.

Feeding Behaviour

Resident killer whale K22 (Sekiu) spy hopping.

Active and opportunistic, orca are the apex predators in the ocean. In fact, they are the largest warm-blooded predator ever known. Fishes, squids, seals, sea lions, walruses, birds, sea turtles, otters, penguins, cetaceans (both mysticete and odontocete), polar bears, reptiles, and even a moose have all been found in the stomach contents of orcas. The diets of orcas vary from one region to another. In the Antarctic, orcas eat about 67% fishes, 27% marine mammals and 6% squid. In the Bering Sea near Alaska, they eat about 65% fishes, 20% squids and 15% marine mammals. The diets of resident and transient orcas differ as well. Resident pods eat a wide variety of fishes and rarely seek out marine mammals. Transient groups primarily eat marine mammals and occasionally eat fishes. Adult orcas eat approximately 3% to 4% of their body weight in food per day; fully weaned calves can eat up to approximately 10% of their body weight during growth periods. Much like packs of wolves or prides of lions, orcas often hunt cooperatively in pods for food. They work together to herd prey into a small area before attacking. When hunting a large whale, a pod of orcas may attack from several angles.

Reproduction

Studies of orcas in marine zoological facilities suggest that females become sexually mature when they reach 4.6–4.9 metres long (16 ft), at about 10–14 years. Males usually become sexually mature when they reach about 5.5–6 m (20 ft), at about 14–19 years. Breeding may occur in any season, but it is most common in the summer. In the North Atlantic, mating seems to peak in October and November; in the western North Pacific, mating seems to be at its highest between May and June, and mating seems to be at its highest between May to September around the Pacific Northwest region (southern resident killer whale community). The gestation period of an orca is about 17 months – the longest known of all cetaceans. A female may bear a calf every 3–5 years totalling approximately 4–6 offspring in her lifetime, although a decade may pass before some have another successful birth.

Calves are born in the water. The majority of deliveries seen by humans have been tail-first births, although a headfirst birth has been observed. Size estimates of captive-born orcas suggest that calves average 2.6 m (8.6 ft) in length and weigh between 136–181 kg (400 lbs). Calves nurse below water, close to the surface. The mother glides in a horizontal position with her tail arched, and the calf swims on its side with its mouth on the right or left mammary gland. The mother’s milk is very rich so that the calf rapidly develops a thick, insulating layer of blubber. The milk fat content fluctuates as the calf develops, ranging from about 48% milk fat at the beginning of the nursing period and gradually decreasing to approximately 28% in the months that follow. A calf may nurse for 12 months or more. A calf may essentially be weaned at one year of age but may continue to nurse occasionally for several more months.

Warnings and Comments

No attack on a human by an orca has ever been recorded (in the wild). Orcas are not yet regarded as an endangered species. In 1946, 14 countries formed the International Whaling Commission (IWC) by signing the International Whaling Convention. The IWC set regulations of whaling to protect the future of whale stocks as a resource to humans. Currently the IWC has no jurisdiction over dolphins such as orcas. However, now that the harvest of most large whales has stopped, the IWC has expressed an interest in playing a role in managing smaller cetaceans as well.