Espolarte - Marine mammals - Killer whale

Killer whale

Orcinus orca


The killer whale, also known as orca, is familiar to most people. It is the largest dolphin, and the only cetacean that regularly eats warm-blooded animals. The orca is a toothed whale, and a member of the oceanic dolphin family (Delphinidae).

Description

The orca is a medium-sized whale and the largest of the delphinids. Length 8 m (males), 7 m (females), max. 9.75 m (males), 8.5 m (females); calves 22.4 m at birth. Max. weight 7200 kg. Body stocky and streamlined, head blunt, beak barely noticeable. Adult males have a tall, triangle-shaped fin; fin of females and juveniles is much smaller. Flippers are large and paddle-shaped; males have larger flippers than females do. Colouration is striking, back is black, belly is white; there is a white spot behind each eye and a saddle-like dark grey patch behind the fin. Orcas usually have 10 to 13 teeth on each side of each jaw.

Identification

The killer whale is fairly common in some areas, and, being unconcerned of shipping, is easy to approach. Due to their long dorsal fins, adult males cannot be confused with any other cetacean. Females and juveniles might be confused with Risso's dolphin or the false killer whale. A dead animal found ashore can easily be identified on the basis of its characteristical shape, even if the skin has already turned in black and the markings have disappeared.

Natural history

Killer whales are top predators of the ocean; they catch, kill and eat any reasonably large animal. Beside fish, they eat dolphins, seals, sea lions, seabirds and even whales much larger than themselves. However, there is no evidence of orcas killing humans in the wild.

We have little knowledge on their reproduction. According to various sources, the gestation period is between 12 and 17 months. As in other cetaceans, only one calf is born at a time. Most calves are born in autumn or early in winter. Mothers lactate their calves for a year.

Killer whales are gregarious animals, living in pods consisting usually of 5-20 animals.

The orca is the fastest swimming marine mammal, capable to a speed of 50 km per hour. Killer whales sometimes breach, leaping clear of water. A typical behaviour is spyhopping (standing vertically with the head above surface). In some occasions, orcas slap the water with their flippers or tail flukes.


Orca spyhopping. Photo: Jaime Ramos. Public domain

Dives usually last 1 to 4 minutes; after a long dive, the animal breathes 3 to 5 times at intervals of 10 to 35 seconds. The longest recorded dive lasted 17 minutes. A captive orca (presumably Ahab or Ishmael) has reached a depth of 260 m; in the wild, the deepest recorded dive was at 173 m.

Like other dolphins, killer whales use echolocation: they orientate and find their prey on the basis of the reflection of sound waves produced by them. They are able to distinguish between two fish of the same size but of different species. They communicate using a variety of calls; some of these calls are within the hearing range of humans. Every orca has its own set of calls. On the basis of the similarity of the sets of calls of two orcas, it is possible to deduce the degree of relationship of the animals.

Live stranding is relatively rare among killer whales, but does occur; males strand more often than females do. Mass strandings have been recorded on the coasts of New Zealand and Vancouver Island.

Distribution

This species occurs worldwide, in all parts of all oceans. Their distribution is limited by the edge of the icepack. They prefer coastal areas of cool climate to tropical regions and open sea. They occur in highest numbers in the Antarctic ocean. The killer whale often ventures into shallow bays and estuaries of rivers. The migration routes are mainly governed by the availability of preferred food rather than by climate. When travelling, orcas cover about 100 km a day.

Status and threats

The killer whale is still relatively common; its conservation status is conservation dependent. The world population of the species can be estimated at 100,000. Killer whale populations are threatened by increasing pollution of oceans and over-fishing of their preferred prey, rather than by deliberate killing. The expanding boat traffic also poses a danger on orcas.

Orcas have been succesfully kept in captivity since the 1960s; they have reproduced in captivity since 1985. In these days (September 2007), 47 animals are kept in 13 zoological gardens. List of orcas currently held in captivity List of orcas died in captivity

More information about killer whales