Physeter macrocephalus commonly known as the Sperm whale, is the largest toothed cetacean. It is easily identified by its distinctive single, slit-like blowhole, which is located on the left side of its head near to the end of its snout. Its blow can project up to 5m tall, is bushy in appearance and is angled forward to the left. Its massive head looks squarish when viewed from the side and is not only one-quarter to one-third of its total length but makes up the greater proportion of the total bulk of the animal. It also features a prominent rounded forehead. The lower jaw is very small, narrow and underslung. Functional teeth are present only in the lower jaw.
It has a laterally compressed body shape and its skin appears wrinkled and prune like on the rear two-thirds of its body. Most sperm whales are brown to blue grey in colour but may have a lighter underside and whitish areas around the mouth. Its flippers are small but wide and spatulate in shape and are set low on the body. Sperm whales have a small triangular shaped rounded dorsal hump that is positioned on the lower part of its back and a series of bumps or ridges that stretch towards the end of the tail. The flukes of this species are broad and triangular with a nearly straight trailing edge, rounded tips, and a deep notch. The shape and pattern of the flukes are used to identify individuals.
Adult male and female Sperm whales can be distinguished by size. Males can measure up to 18m and weigh as much as 57 tonnes, whereas the smaller females grow to about 11m in length and weigh about 10-12 tonnes. They can live to about 60-70 years.
Sperm whales are present worldwide from tropical to oceanic waters, although generally only large males venture to the extreme northern and southern portions of the range. This species has also been recorded off the East African coast and throughout the western Indian Ocean all year round. Resident populations have been identified off the west coast of Mauritius and around the Seychelles. They can be seen close to shore but only where there are submarine canyons or deep water near to the coast. They prefer deep waters and can dive to depths in excess of 200m where they hunt for fish, cephalopods; squid and octopuses. Sperm whales use echolocation and produce low-frequency clicks which are termed “codas,” used for navigation, to locate and track prey and probably for communication. Some clicks are distinct to individual sperm whales and are thought to act as acoustic signatures.
This species of whale is often found in medium to large groups of up to fifty individuals made up of females and their offspring. Mature males travel alone or in small groups. They are polygynous and adult males join nursery groups of adult females and their offspring for mating, for short periods of time. Sexual maturity is reached for both males and females at about 9 years, but males are not physically fully mature until they are 20 year of age. Females are pregnant for 15 -16 months and new-born calves are 3.5 to 4.5 m long, claves are nursed for about 2 years. Most births occur between January and April in the western Indian Ocean and in summer or autumn in other areas around the world, the calving interval is about 5 years.
Physeter macrocephalus is listed as ‘Vulnerable’ on the IUCN Red List of Threatened Species and the current population trend is unknown. Sperm whales were heavily commercially targeted and hunted between the 18th and the 20th centuries. The species is on Appendix I of CITES and Appendices I and II of CMS. The International Whaling Commission manages sperm whale populations under the International Convention for the Regulation of Whaling. A moratorium on whaling came into effect in 1986. However, many range states are not members of the International Whaling Commission.
Sperm whale populations are also threatened by shipping, industrial & military effluents agricultural & forestry effluents as well as garbage & solid waste which has been found in the stomachs of individuals.
The sperm whale’s head is large because it contains a huge cavity called the spermaceti organ which is thought to help the whale control buoyancy and dive to deep depths. It may also be used to help focus sonar clicks.
The sperm whale produces a substance called ambergris or grey amber, which is a waste product of its digestive system. It is wax like and can be found floating at sea or in lumps on beaches. It was previously used in the perfume industry.
Carwardine M. (2000) Whales Dolphins and Porpoises. London, Dorling Kindersley Ltd.
Jefferson, T.A., Leatherwood S. and Webber M.A. Marine Mammals of the World retrieved from Marine Species Identification Portal http://species-identification.org/index.php