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Sperm Whale

Physical description

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Perhaps the most widely known and well-recognised of all the cetaceans. At a distance its blow is easily identified being angled forwards and to the left. Its body shape is unique with a square, blunt head which is about 1/3 of the total body length. Sperm whales have a single s-shaped blowhole at the left side of the front of the head and their long, narrow lower jaw fits neatly into the underside of the head. The pectoral fins are small and broad, with rounded tips and instead of a distinct dorsal fin there are a series of small humps leading to the tail. The flukes are broad and triangular and are lifted high before a dive. Their skin is wrinkled and splotchy grey/blue. Mature males can be one and a half times the length of mature females and the females often have calluses on their dorsal humps. Their conical teeth are found only in the lower jaw and they fit into sockets in the upper jaw.

Distribution
Sperm whales are found in all deep ocean waters right up to the polar ice fields. They have evolved to live in these deep waters and are in serious danger of stranding when they move inshore. Most commonly found in submarine canyons at the edge of the continental shelf. There is a general movement towards the poles during the summer though some populations are resident all year round. Although the most heavily exploited of all the whales it is still relatively abundant.

Behaviour

Sperm whales make long, deep dives possibly up to 3,000 metres. They are known to be able to remain submerged for up to 2 hours though typical dives last usually about 45 minutes with intervals of about 15 minutes. Before a deep dive the sperm whale lifts its flukes and dives straight down, returning to the same spot when it surfaces. They often breach and lobtail.


Breeding
Males reach maturity at about 10 years of age and females between 8 and 11 years but they spend most of their lives in either bachelor or nursery schools of up to 50 individuals. The females remain in the nursery schools with the young and other females of any age and mature bulls only visit during the breeding season. Gestation lasts about 18 months and calves are suckled for up to 2 years. Sperm whales are thought to live for 75 years or more.

Feeding

Sperm whales feed mostly on deep ocean squid and octopus and their fights with the giant squid which can grow up to 16 metres in length are legendary. Though these fights have never been witnessed, sperm whales adults have been found with scars from squid tentacles and teeth and the beaks of the giant squid have been found in their stomachs.

Current situation
Although they are not under threat from whaling today, their numbers were seriously depleted in the last two centuries. The greatest threats today are from pollution and noise disturbance which interferes with their complex echolocation and use of sound. They are also often entangled in nets.