The Sperm Whale

(Physeter macrocephalus)

Although the Sperm whale is easily identified it rarely shows much of its body above the water. This whale has a very distinctive huge squarish head occupying at least one-third of its body and projecting, often up to 1.5m (5ft), well beyond its lower jaw. The large head contains a cavity called the spermaceti organ which is a mass of web-like tubes filled with a yellow wax. This organ is believed to be used in maintaining buoyancy and may also be used to focus sonar clicks.

The Sperm whale has a robust body with corrugations in the skin giving it a shrivelled prune-like appearance. The skin is dark grey or brownish grey. It is paler at the front of the head and on the belly, with white fringes to the mouth particularly in the corners.

From the Suborder Odontoceti (toothed whale) the Sperm whale has in the lower jaw 20-25 large conical functional teeth (unpaired) in the male and fewer, smaller teeth in the female. The upper jaw has up to 10 frequently curved teeth in the male and none in the female. The teeth often erupt only at sexual maturity and then, in males, only in the lower jaw.

The Sperm whale has one blowhole which gives a bushy blow projected forwards at a sharp angle to the left. There are two openings to the nasal passage divided by an external central septum but these are internal. The whale has no dorsal fin but it has a distinct triangular or rounded hump two-thirds along the body followed by a spinal ridge to broad triangular and deeply notched tail flukes. A thick 'keel' not seen in many whales runs along the underside of the tail stock.

Superfamily: Physeteroidea

Family: Physeteridae

Other names: Cachalot, Great Sperm whale, Physeter catodon

Food: Squid, octopus, fish - [N.Hemis.] rock fish, skate, angler fish, lumpsucker, cod, brown ragfish, [S.Hemis.] cusk eel, rough fish, groper, king-fish, eels.

The Sperm whale is cosmopolitan in deep waters of all seas except close to ice edges. It is most common in submarine trenches at the edge of the continental shelf but may occur inshore where water is deeper than 200m (655ft). Migration to favoured areas for feeding and breeding may be undertaken however females undergo less extensive seasonal migration than males, usually only to 40°north and south of the Equator. Males regularly travel to 65°north and 70°south. Winter is spent in temperate and tropical waters. Some populations are resident year-round.

Feeding areas include deeper waters around the Aleutian Islands in North Pacific, off New Zealand, Peru and Chile in the South Pacific, Newfoundland Grand Banks and the continental slope west of the British Isles, north towards Iceland in the North Atlantic, east coast of South America from Argentina to the Faulkland Islands and around Tristan da Cunha in the South Atlantic.

Mating and calving areas include waters off New Guinea and around Hawaii in the North Pacific, deep waters off East Australia, Galapagos and Ecuador in the South Pacific, around the Bahamas, the Azores and Madeira in the North Atlantic, off Brazil, Angola and Southwest Africa in the South Atlantic, off Western Australia, around Madagascar, and west and north of Seychelles to the coasts of India, Sri Lanka and the Arabian peninsula in the Indian Ocean.

The world population size has been reduced by whaling and the estimated curent number of Sperm whales is 1,900,000