Sperm whales which belong to the suborder of toothed whales and dolphins (odontocetes) are one of the easiest whales to identify at sea. The angled bushy blow is distinctive from a distance, sperm whales have a single blowhole on the left side, near the front of the head, and close up its enormous square-shaped head and wrinkly skin are unmistakable. The skin is dark grey or brownish grey, with white markings around the lower jaw and underside. The sperm whale's huge head, which is up to 1/3 of its overall body length, houses the heaviest brain in the animal kingdom. It also contains a cavity large enough for a small car to fit inside which holds a yellowish wax known as spermaceti oil, thought to help in buoyancy control when diving and act as an acoustic lens. They have between 40-52 teeth in their long, narrow lower jaw. These are thick and conical, and can grow to 20cm long and weigh 1kg each. Sperm whales have relatively short, stubby flippers and a low hump instead of a dorsal fin, with 'knuckles' stretching from the hump along their backs to their triangular tail flukes, which are raised when diving. Most females, but few males, have calluses on the dorsal hump.
During the days of commercial whaling, sperm whales were so named because when the head was cut open it was found to contain a milky white substance, and the whalers thought the large square head was a huge reservoir for sperm. Additionally, an intestinal secretion called ambergris is found in sperm whales which was used as a fixative in the perfume industry and was at one time worth more than its weight in gold (this is no longer the case).
Sperm whales are thought to dive deeper than any other mammal in the world and the sperm whale is the champion 'free-diver' of the whale world. Typically they make dives of up to 400 m, but they can reach depths of up to 2-3km. They are thought to be able to hold their breath for up to two hours, although 45 minutes is the average dive time. Some sperm whales have scars on their bodies caused by giant squid tentacles during fights. Although sperm whales are known to eat a wide variety of sea creatures their major prey items are deep-water squid which they are believed to 'catch' by the suction method of eating. Sperm whales can be quite gregarious and are known to breach, spyhop and lobtail. Sperm whales spend most of their lives in either 'nursery schools' (adult females with young) or 'bachelor schools' (males between seven and 27 years of age) although older males tend to live on their own or in very small groups and join nursery schools during the breeding season. The only natural predator of the sperm whale is the orca and even then most attacks are not thought to be fatal. During such attacks however, the females show defensive behaviour of calves by creating a ring with the calves in the centre – called a 'marguerite'. These rings may have their heads or tails on the outside.
Sperm whales are found in most of the world's oceans, except the high Arctic and prefer deep water. They can be found in large numbers where food is abundant, and where the sea temperature suits them. This species has been drastically affected by commercial whaling in the past and numbers are thought to have been decimated. Sperm whales are still threatened by hunting - principally by Japan. Sperm whales are at risk from human disturbance and whaling, chemical and noise pollution and entanglement in fishing nets. The current worldwide population is not known and the conservation status of the sperm whale is listed as Vulnerable (IUCN 2008).