Killer Whale

Physical Description

The orca is a stout, streamlined animal. It has a round head that is tapered, with an indistinct beak and straight mouth line. The orca has a striking color pattern made up of well- defined areas of shiny black and cream or white. The dorsal (top) part of its body is black, with a pale white to gray “saddle” behind the dorsal fin. It has an oval, white eyepatch behind and above each eye.

The chin, throat, central length of the ventral (underside) area, and undersides of the tail flukes are white. Each whale can be individually identified by its markings and by the shape of its saddle patch and dorsal fin.

Length & Weight

Males can grow as large as 9.6 metres long and weigh 8 to 9 tonne. Females can reach 8.2 metres in length and weigh up to 4 tonne. Another distinctive feature of the orca is its dorsal fin, which can reach 1.8 metres high in males and is shaped like an isosceles triangle. The immature male and the female dorsal fins are also large, reaching 1 metre high, but are falcate (curved).

The dorsal fin often has identifying nicks, cuts, scars and indentations. The paddle-shaped pectoral flippers are broad, rounded, and can reach a length of nearly 1.8 metres and a width of 1 metre.

Mating and Breeding

Little is known about the orca’s breeding habits. Newborn calves have been observed throughout the year suggesting that mating can occur at any time with no particular breeding season. In the wild, orcas become sexually mature between the ages of 10 and 18 years of age and are thought to be actively reproducing by the time the male reaches about 5.1 metres in length and the female reaches about 4.1 metres. Females are believed to be reproductively active into their early 40’s. the gestation period is estimated to be between 13 to 17 months. At birth, a calf is generally between 1.8 – 2.1 metres and weighs around 180 kilograms.

Feeding

The mouth of the orca is large and well adapted for hunting. It has 46 to 50 conical shaped teeth that point slightly backwards and inwards. The upper and lower teeth interlock, which aids in gripping large prey and tearing it into smaller pieces for easier swallowing.

Depending on the population and geographic area, the diet of orcas varies. Food preference and availability may have led to the distinct population types which can be residents, transients and offshores. Generally transients will feed on a variety of animals (seals, fish, penguins and whales) whilst residents tend to feed primarily on fish species such as herring or salmon. The diet of offshores is still being studied.

Distribution and Migration

The orca is found in all oceans of the world, though they are more abundant in cooler waters. Unlike some species of whales, which follow a regular migration route each year, the orca seems to travel according to the availabilty of food. They are one of the few species of whales that move freely from hemisphere to hemisphere.

Natural History

Orcas generally live in pods (groups) consisting of several females, calves, one or more males, and/or juveniles. Some pods consist of a mother and her offspring who stay with her for life. This type of matrilineal family structure has been observed in the

U.S. Pacific Northwest where resident pods have been documented as stable, consistent matriarchal family groups with several generations travelling together. Transient pods appear to be more fluid; individuals come and go, groups often contain unrelated females with offspring, offspring do not stay with their mother and pods may form solely as a temporary foraging pack.

Status

Although orcas are widely distributed, total world population is still unknown. They have no natural enemies and have not been hunted as much as other whales. Recent studies suggest that a significant threat to orcas, and other marine mammals, may come from man-made chemicals. Yet, toxins are not the only threats facing orcas. Many fish populations around the world are decreasing. This may be having a direct effect on the populations of fish- eating resident whales. Loss of fish may also cause a decline in seals and sea lions, often the primary prey of transient orcas.

Acknowledgements
Australian Museum; American Cetacean Society; National Geographic Society; Department of the Environment, Water, Heritage and the Arts