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Sperm whales live in either nursery or bachelor groups. Nursery groups consist of a number of adult females and immature males and females (2) (6). Males leave these groups when they become mature and join bachelor groups, which consist of males of 7 to 27 years of age (6). Older males live in small groups or singly, and visit nursery groups to mate with females during the breeding season (6). Most groups of sperm whales tend to number between 10 and 15 individuals (4). Sperm whales use echolocation to find their prey in the dark ocean depths (6). When foraging, powerful sound waves are emitted from the large head; these can stun and even kill the squid, octopuses and fish on which they feed (4). These whales make deep dives to depths of up to 3,000 meters (almost 2 miles) that can last as long as two hours (2) (6). This is the deepest dive made by any species of mammal (6). Males reach maturity at 10 years of age, but they do not begin to mate until they are around 19 years old and a length of 13 metres. Females become mature at between 7 and 11 years, when they are around nine metres in length. A single calf is born between July and November after a gestation period of around 16 months. The calf is suckled for up to two years (4). Groups of females protect their young by adopting a defensive 'marguerite formation' in which the calves are placed in the centre of the group surrounded by a circle of females, facing tail outwards (4).

As a species, the sperm whale is not facing immediate threat, but some populations need to be carefully monitored, and there is need for tight management of any exploitation (1). In the eastern tropical Pacific, recent whaling was extremely intensive, and birth rates at present are very low. The Mediterranean population is particularly susceptible to collisions with ships and entanglement with fishing gear (1).

The sperm whale is the largest of the toothed whales, with males growing up to 20 metres in length. It also has the largest brain of any living animal, and it was a sperm whale that was pitted against Captain Ahab in Herman Melville's classic novel, Moby Dick (2). Sperm whales have huge square heads, comprising almost a third of the total body length (2) (3); indeed the specific name macrocephalus means large head. Uniquely among cetaceans, the single blowhole is located on the left of the head rather than on the top (3) and so these whales are easily identified at a distance by their low, bushy spout, which is projected forward and slightly to the left (2). Further down the body toward the tail there is usually a large hump on the back, followed by a series of smaller bumps (3). The dark brown to bluish-black skin, which is splotched and scratched, is said to have a texture like that of a plum stone (2) (3). Males tend to be somewhat larger and heavier than females (3), and have larger heads in relation to their body size (6). The huge heads of sperm whales contain a large cavity, the spermaceti organ, filled with a waxy liquid called spermaceti oil. This wax can be cooled or heated, possibly by water sucked in through the blowhole, and thus shrinks and increases in density (helping the whale sink), or expands and decreases in density (helping the whale rise to the surface) (5). Whalers likened the substance to semen, and this is the origin of the common name of the species (6).

Inhabits the open ocean in offshore areas, although providing that water is deeper than 200 metres they may occasionally be seen closer to land (2). They occur in tropical to sub-polar waters (2).

Sperm whales are found in all of the oceans of the world, except the high Arctic (6).

Classified as Vulnerable (VU) on the IUCN Red List 2007 (1) and listed under Appendix I of CITES (4).

Sperm whales have a long history of commercial exploitation (1). Large-scale hunting began in 1712 in the North Atlantic, based at Nantucket in America (4). They were not widely hunted for their meat, but for ambergris and spermaceti. Ambergris is a substance that collects around the indigestible beaks of squid in the stomach of the whale, and was highly prized for use as a fixative in the perfume industry. Although artificial alternatives are now available, some perfume makers prefer to use ambergris today. Spermatceti was used in the production of cosmetics and candles (7). Sperm whales still have an economic value today for meat in Japan. Since the 1980s, the International Whaling Commission brought an international moratorium on whaling into force. Despite this measure, Japan continues to hunt sperm whales, and relatively small numbers are taken each year with hand harpoons at Lamalera, Indonesia (1). Further threats include entanglement in fishing gear and collisions with boats (1). Although whaling has, with the exceptions outlined above, largely ceased, the after-effects of such prolonged and intensive hunting are still being felt today. It is thought that the selective hunting of the largest, breeding males will have decreased pregnancy rates, and the loss of the largest females from nursery groups would have decreased the survival of the groups (1).