Sperm whale
The sperm whale or cachalot is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus Physeter and one of three extant species in the sperm whale superfamily Physeteroidea, along with the pygmy sperm whale and dwarf sperm whale of the genus Kogia.
The sperm whale is a pelagic mammal with a worldwide range, and will migrate seasonally for feeding and breeding. Females and young males live together in groups, while mature males live solitary lives outside of the mating season. The females cooperate to protect and nurse their young. Females give birth every four to twenty years, and care for the calves for more than a decade. A mature, healthy sperm whale has no natural predators, although calves and weakened adults are sometimes killed by pods of killer whales.
Mature males average in length, with the head representing up to one-third of the animal's length. Plunging to, it is the third deepest diving mammal, exceeded only by the southern elephant seal and Cuvier's beaked whale. The sperm whale uses echolocation and [|vocalization] with source level as loud as 236 decibels underwater, the loudest of any animal. It has the largest brain on Earth, more than five times heavier than a human's. Sperm whales can live 70 years or more.
Sperm whales' heads are filled with a waxy substance called "spermaceti", from which the whale derives its name. Spermaceti was a prime target of the whaling industry and was sought after for use in oil lamps, lubricants, and candles. Ambergris, a solid waxy waste product sometimes present in its digestive system, is still highly valued as a fixative in perfumes, among other uses. Beachcombers look out for ambergris as flotsam. Sperm whaling was a major industry in the 19th century, depicted in the novel Moby-Dick. The species is protected by the International Whaling Commission moratorium, and is listed as vulnerable by the International Union for Conservation of Nature.
Taxonomy and naming
Etymology
The name "sperm whale" is a clipping of "spermaceti whale". Spermaceti, originally mistakenly identified as the whales' semen, is the semi-liquid, waxy substance found within the whale's head.The sperm whale is also known as the "cachalot", which is thought to derive from the archaic French for 'tooth' or 'big teeth', as preserved for example in the word caishau in the Gascon dialect.
The etymological dictionary of Corominas says the origin is uncertain, but it suggests that it comes from the Vulgar Latin cappula 'sword hilts'. The word cachalot came to English via French from Spanish or Portuguese, perhaps from Galician/Portuguese 'big head'.
The term is retained in the Russian word for the animal, , as well as in many other languages.
The scientific genus name Physeter comes from the Greek , meaning 'blowpipe, blowhole ', or – as a pars pro toto – 'whale'.
The specific name macrocephalus is Latinized from the Greek , from + .
Its synonymous specific name catodon means 'down-tooth', from the Greek elements and ; so named because it has visible teeth only in its lower jaw.
Another synonym australasianus was applied to sperm whales in the Southern Hemisphere.
Taxonomy
The sperm whale belongs to the order Cetartiodactyla, the order containing all cetaceans and even-toed ungulates. It is a member of the unranked clade Cetacea, with all the whales, dolphins, and porpoises, and further classified into Odontoceti, containing all the toothed whales and dolphins. It is the sole extant species of its genus, Physeter, in the family Physeteridae. Two species of the related extant genus Kogia, the pygmy sperm whale Kogia breviceps and the dwarf sperm whale K. sima, are placed either in this family or in the family Kogiidae. In some taxonomic schemes the families Kogiidae and Physeteridae are combined as the superfamily Physeteroidea.Swedish ichthyologist Peter Artedi described it as Physeter catodon in his 1738 work Genera piscium, from the report of a beached specimen in Orkney in 1693 and two beached in the Netherlands in 1598 and 1601. The 1598 specimen was near Berkhey.
The sperm whale is one of the species originally described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae. He recognised four species in the genus Physeter. Experts soon realised that just one such species exists, although there has been debate about whether this should be named P. catodon or P. macrocephalus, two of the names used by Linnaeus. Both names are still used, although most recent authors now accept macrocephalus as the valid name, limiting catodon status to a lesser synonym. Until 1974, the species was generally known as P. catodon. In that year, however, Dutch zoologists Antonius M. Husson and Lipke Holthuis proposed that the correct name should be P. macrocephalus, the second name in the genus Physeter published by Linnaeus concurrently with P. catodon.
This proposition was based on the grounds that the names were synonyms published simultaneously, and, therefore, the ICZN Principle of the First Reviser should apply. In this instance, it led to the choice of P. macrocephalus over P. catodon, a view re-stated in Holthuis, 1987. This has been adopted by most subsequent authors, although Schevill argued that macrocephalus was published with an inaccurate description and that therefore only the species catodon was valid, rendering the principle of "First Reviser" inapplicable. The most recent version of ITIS has altered its usage from P. catodon to P. macrocephalus, following L. B. Holthuis and more recent discussions with relevant experts. Furthermore, The Taxonomy Committee of the Society for Marine Mammalogy, the largest international association of marine mammal scientists in the world, officially uses Physeter macrocephalus when publishing their definitive list of marine mammal species.
Biology
External appearance
| Length | Weight | |
| Male | ||
| Female | ||
| Newborn |
The sperm whale is the largest toothed whale and is among the most sexually dimorphic of all cetaceans. Both sexes are about the same size at birth, but mature males are typically 30% to 50% longer and three times as massive as females.
Newborn sperm whales are usually between long. Female sperm whales are sexually mature at in length, whilst males are sexually mature at. Female sperm whales are physically mature at about in length and generally do not achieve lengths greater than. The largest female sperm whale measured up to long, and an individual of such size would have weighed about. Male sperm whales are physically mature at about in length, and larger males can generally achieve. A male sperm whale measuring in length is estimated to have weighed. By contrast, the second largest toothed whale measures up to and weighs up to.
There are occasional reports of individual sperm whales achieving even greater lengths, with some historical claims reaching or exceeding. One example is the whale that sank the Essex, which was claimed to be. However, there is disagreement as to the accuracy of some of these claims, which are often considered exaggerations or as being measured along the curves of the body.
An individual measuring was reported from a Soviet whaling fleet near the Kuril Islands in 1950 and is cited by some authors as the largest accurately measured. It has been estimated to weigh. In a review of size variation in marine megafauna, McClain and colleagues noted that the International Whaling Commission's data contained eight individuals larger than. The authors supported a male from the South Pacific in 1933 as the largest recorded. However, sizes like these are rare, with 95% of recorded sperm whales below 15.85 metres.
In 1853, one sperm whale was reported at in length, with a head measuring. Large lower jawbones are held in the British Natural History Museum and the Oxford University Museum of Natural History, measuring and, respectively. The blunt, square snout can reach up to at the tip of the lower jaw.
The average size of sperm whales has decreased over the years, probably due to pressure from whaling. Another view holds that exploitation by overwhaling had virtually no effect on the size of the bull sperm whales, and their size may have actually increased in current times on the basis of density dependent effects. Old males taken at Solander Islands were recorded to be extremely large and unusually rich in blubbers.
The sperm whale's unique body is unlikely to be confused with any other species. The sperm whale's distinctive shape comes from its very large, block-shaped head, which can be one-quarter to one-third of the animal's length. The S-shaped blowhole is located very close to the front of the head and shifted to the whale's left. This gives rise to a distinctive bushy, forward-angled spray.
The sperm whale's flukes are triangular and very thick. Proportionally, they are larger than that of any other cetacean, and are very flexible. The whale lifts its flukes high out of the water as it begins a feeding dive. It has a series of ridges on the back's caudal third instead of a dorsal fin. The largest ridge was called the 'hump' by whalers, and can be mistaken for a dorsal fin because of its shape and size.
In contrast to the smooth skin of most large whales, its back skin is usually wrinkly and has been likened to a prune by whale-watching enthusiasts. Albinos have been reported.
Skeleton
The ribs are bound to the spine by flexible cartilage, which allows the ribcage to collapse rather than snap under high pressure. While sperm whales are well adapted to diving, repeated dives to great depths have long-term effects. Bones show the same avascular necrosis that signals decompression sickness in humans. Older skeletons showed the most extensive damage, whereas calves showed no damage. This damage may indicate that sperm whales are susceptible to decompression sickness, and sudden surfacing could be lethal to them.Like that of all cetaceans, the spine of the sperm whale has reduced zygapophysial joints, of which the remnants are modified and are positioned higher on the vertebral dorsal spinous process, hugging it laterally, to prevent extensive lateral bending and facilitate more dorso-ventral bending. These evolutionary modifications make the spine more flexible but weaker than the spines of terrestrial vertebrates.
Like many cetaceans, the sperm whale has a vestigial pelvis that is not connected to the spine.
Like that of other toothed whales, the skull of the sperm whale is asymmetrical so as to aid echolocation. Sound waves that strike the whale from different directions will not be channeled in the same way. Within the basin of the cranium, the openings of the bony narial tubes are skewed towards the left side of the skull.