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Sperm Whale

The Sperm Whale (Physeter macrocephalus) is the largest of the toothed whales and is the largest toothed animal in the world. The whale was named after the milky-white substance spermaceti found in its head and originally mistaken for sperm. The Sperm Whale's enormous head and distinctive shape, as well as its central role in Herman Melville's Moby Dick, have led many to describe it as the archetypal whale. Partly due to Melville, the Sperm Whale is commonly associated with the quasi-mythic Leviathan of Biblical lore.

Historically the Sperm Whale has also been known as the Common Cachalot.

Physical description: The Sperm Whale is exceptional for its very large head, particularly in males, which is typically one-third of its length. Indeed, the species name macrocephalus is derived from the Greek for 'big head'. In contrast to the smooth skin of most other large whales, the skin on the back of the Sperm Whale is usually knobbly and has been likened to a prune by whale-watching enthusiasts (ref 5. below). They are uniformly grey in colour though may appear brown in sunlight (the "Great White Whale" of Melville's novel, if such an animal existed, was an albino). Perhaps unsurprisingly, the brain of the Sperm Whale is the largest and heaviest of all animals (weighing on average 7 kg in a grown male). However, the brain is not large relative to body size.

The blowhole is situated very close to the front of the head and shifted to the left (as observed when facing the same direction as the whale). This gives rise to a distinctive bushy blow angled forward. The dorsal fin is set about two-thirds of the way down the spine and is typically short and shaped like an equilateral triangle. The fluke is also triangular and very thick. Flukes are lifted very high out of the water before a whale begins a deep dive.

Sperm Whales have 20-26 pairs of cone-shaped teeth in their lower jaw. Each tooth can weigh as much as one kilogram. The reason for the existence of the teeth is not known with certainty. It is believed that they are not necessary for feeding on squid (see Feeding below) and indeed healthy well-fed Sperm Whales have been found in the wild without teeth. The current scientific consensus is that the teeth may be used for aggression between males of the same species. This hypothesis is consistent with the conic shape and wide-spacing of the teeth. Rudimentary teeth are also present in the upper jaw but these rarely open into the mouth.

Sperm Whales are amongst the most sexually dimorphic (that is, males and females differ greatly) of all cetaceans. Males are typically 30-50% longer (16-18m) than females (12-14m) and weigh about twice as much (50,000kg vs 25,000kg). At birth both males and females are about 4m in length and 1,000kg in weight.

Geneticists describe Sperm Whales as the epitome of a species that has been K-selected, which is to say that the species is believed to have developed primarily under evolutionary pressure from individuals of the same species. This relatively 'easy' evolution has led them to have a low birth rate, slow maturation and high longevity. Females give birth once every four to six years and the gestation period is at least 12 months and possibly as long as 18 months. Nursing takes place for two to three years. In males puberty lasts for about ten years between the ages of about 10 and 20. Males continue to grow into their 30s and 40s and only reach their full size when about 50 years old. Sperm Whales live for up to 80 years.

Taxonomy:
The Sperm Whale was categorised first by Linnaeus in 1758 who recognised four species in the Physeter genus. Authorities soon realised that just one such species exists. In most modern publications the Sperm Whale is classified as the sole species in the Physeteridae family (and thus the only species in its genus). The Sperm Whale family is sometimes (see e.g. [4]) treated as a superfamily, Physeteroidea. This superfamily contains only two other species - the Pygmy Sperm Whale and the Dwarf Sperm Whale. These two whales belong to the family Kogiidae. Mead and Brownell (1993, see [6]), however, list all three species in the family Kogiidae, give the Sperm Whale the binomial name Physter catodon and dispense with the superfamily.

A worthwhile extract from Melville's Moby Dick, in which he expatiates about the naming and common lore surrounding the Sperm Whale, is hereunder reproduced:

"This whale, among the English of old vaguely known as Trumpa whale, and the Physeter whale, and the Anvil Headed whale, is the present Cachalot of the French, the Pottfisch of the Germans, and the Macrocephalus of the Long Words. [text omitted] It is chiefly with his name that I now have to do. Philologically considered, it is absurd. Some centuries ago, when the Sperm whale was almost wholly unknown in his proper individuality, and when his oil was only accidentally obtained from the stranded fish; in those days spermaceti, it would seem, was popularly supposed to be derived from a creature identical with the one then known in England as the Greenland or Right Whale. It was the idea also, that this same spermaceti was that quickening humor of the Greenland Whale which the first syllable of the word literally expresses. In those times, also, spermaceti was exceedinly scarce, not being used for light, but only as an ointment and medicament. It was only to be had from the druggists as you nowadays buy an ounce of rhubarb. When, as I opine, in the course of time, the true nature of spermaceti became known, its original name was still retained by the dealers; no doubt to enhance its value by a notion so strangely significant of its scarcity. And so the appellation must at last have come to be bestowed upon the whale from which this spermaceti was really derived.

Sperm Whales are believed to have diverged from other toothed whales early in the evolution of the suborder - around twenty million years ago.

Spermaceti: Spermaceti is the semiliquid waxy substance found in the head of the Sperm Whale. The name derives from the late Latin sperma ceti (sperma is actually a loan word from Greek) meaning 'sperm of the whale' (strictly, 'sperm of the sea monster'). The common name for the species is actually an apocopation of Spermaceti Whale. The substance is not of course the whale's semen; it was mistaken for such by early whalers. Spermaceti is found in the spermaceti organ or case in front of and above the skull of the whale and also in the so-called junk which is right at the front of the whale's head just above the upper jaw. The case consists of a soft white substance saturated with spermaceti. The junk is a more solid substance.

The precise function of spermaceti and the organs it fills is not known but at least three (not necessarily mutually exclusive) hypotheses exist:

One hypothesis (detailed in [12]), incidentally discussed in Moby Dick by Melville, is that the case evolved as a kind of battering ram for use in fights between males. This hypothesis is consistent with the well-documented sinking of the ships Essex and Ann Alexander due to attacks by Sperm Whales estimated to weigh only one fifth as much as the ships. The role of spermaceti as a sexual selector is currently the most in vogue.

A second, more long-standing, suggestion is that the case is an aid to the whale in controlling buoyancy. The density of the wax could be increased by cooling it with water brought in through the blowhole, helping the whale to sink. Conversely, forcing water out through the blowhole again would cause the spermaceti to reheat, become less dense and aid floating. This popularly-quoted theory has recently lost some credence. Research suggests that no capillary effect would be extensive enough to change drastically the buoyancy of a 50-tonne whale. (See Ted Cranford's homepage [13] for a list of papers detailing the research).

A third possibility is that the case is used as an aid to echolocation. The shape of the organ at any given time is likely to focus or widen the beam of emitted sound. The sound waves may be so focused that they act as a kind of stun gun, temporarily disabling prey. Active research into all these possibilities continues.

Spermaceti was much sought after by 18th, 19th and 20th century whalers. The substance found a variety of commercial applications, such as watch oil, automatic transmission fluid, lubricant for delicate high altitude instruments, cosmetics, additives in motor oils, glycerine, rust-proofing compounds, detergent, chemical fibers, vitamins and 70 or more pharmaceutical compounds.