Sperm Whale

Physical Description

The Sperm Whale is the largest of the toothed whales and is the best known member of the whale family. The most distinctive feature is the large blunt and squared off head and the small, underslung jaw. The head makes up to 1/3 of the total body length and more than 1/3 of the whale’s mass. A single blowhole is located forward on the left side of the head and the blow is projected forward, rather than straight up as it is with other whales.

Its body has a shriveled appearance, particularly behind the head. The sperm whale is usually a dark, brownish grey with light streaks, spots and scratches. The skin around the mouth, particularly near the corners, is white. The underside is a lighter grey and may have white patches.

Length & Weight

Adult males reach lengths of 15 – 18 metres and weigh up to 30 to 50 tonne while adult females are much smaller, growing to about 11 metres with a maximum weight of around 13 tonne. The brain of the sperm whale is the largest of any animal averaging 6.5kg and reaching up to 9kg.

Mating and Breeding

Males reach sexual maturity at approximately 10 – 12m and 10 years or more of age but do not appear to take part in breeding activity until they reach their late 20’s. Females reach sexual maturity at 8 – 9m and 7 – 13 years of age. Gestation is between 14 – 16 months and newborm calves weigh approximately 1 tonne and are 3.5 – 5.0m long. Mothers nurse their calves for 2 years or longer.

Feeding

The main source of food is medium sized deep water squid, but it also feeds on fish, octopus and smaller squid. A sperm whale consumes about 1 tonne of food each day. The lower jaw contains 18 – 25 large teeth on each side of the jaw, 7-18 centimetres in length. The upper jaw may have tiny teeth but they rarely erupt. The upper jaw contains a series of sockets into which the lower teeth fit.

Distribution and Migration

Sperm whales are found in all oceans of the world. The males, alone or in groups, are found in the higher latitudes. They migrate toward the lower latitudes where the largest males enter the breeding grounds close to the equator. Females, calves and juveniles remain in the warmer tropical and sub- tropical waters of the Pacific, Atlantic and Indian Oceans year round.

They tend to prefer deeper waters and generally remain along the edge of continental shelves in water 1 to 3 kilometres deep or further out to sea.

Natural History

Sperm whales are found in all oceans of the world. The males, alone or in groups, are found in the higher latitudes. They migrate toward the lower latitudes where the largest males enter the breeding grounds close to the equator. Females, calves and juveniles remain in the warmer tropical and sub- tropical waters of the Pacific, Atlantic and Indian Oceans year round. They tend to prefer deeper waters and generally remain along the edge of continental shelves in water 1 to 3 kilometres deep or further out to sea.

Status

Sperm whales are still fairly numerous, but selective killing of the larger breeding-age males over many years upset the male to female ratio and the numbers of some populations has seriously declined. Recent estimates indicate that the global population is approximately 360,000 animals down from about 1.1 million prior to commercial whaling.

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