Sperm Whale

The sperm whale, Physeter macrocephalus, is a marine mammal species, order Cetacea, a toothed whale (odontocete) having the largest brain of any animal. The name comes from the milky-white waxy substance, spermaceti, found in the animal's head. The sperm whale is the only living member of genus Physeter. The synonym Physeter catodon refers to the same species. It is one of three extant species in the sperm whale superfamily, along with the pygmy sperm whale and dwarf sperm whale.

A bull can grow to 20.5 m long. It is the largest living toothed animal. The head can represent up to one-third of the animal's length. It has a cosmopolitan distribution across the oceans. The species feeds on squid and fish, diving as deep as 3 km, which makes it the deepest diving mammal. Its diet includes giant squid and colossal squid. The sperm whale's clicking vocalization is the loudest sound produced by any animal, but its functions are uncertain. These whales live in groups called pods. Pods of females and their young live separately from older males. The females cooperate to protect and nurse their young. Females give birth every three to six years, and care for the calves for more than a decade. The sperm whale has few natural predators, since few are strong enough to successfully attack a healthy adult; orcas attack pods and kill calves. The sperm whale can live for more than 70 years.

Historically, the sperm whale was also known as the common cachalot; "cachalot" is derived from an archaic French word for "tooth". Over most of the period from the early 18th century until the late 20th century, the sperm whale was hunted to obtain spermaceti and other products, such as sperm oil and ambergris. Spermaceti found many important uses, such as candles, soap, cosmetics and machine oil. Due to its size, the sperm whale could sometimes defend itself effectively against whalers. In the most famous example, a sperm whale attacked and sank the American whaleship Essex in 1820. As a result of whaling, the sperm whale is currently listed as vulnerable by the IUCN.

Name
The name sperm whale is an apocopation of spermaceti whale. Spermaceti, originally mistaken for the whales' "sperm", is the semi-liquid, waxy substance found in the spermaceti organ or case in front of and above the skull bone and also in the junk, the area below the spermaceti organ and just above the upper jaw. The case consists of a soft white, waxy substance saturated with spermaceti oil. The junk is composed of cavities filled with the same wax and spermaceti oil and intervening connective tissue. 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 cachau in the Gascon dialect (a word of either Romance or Basque origin). The etymological dictionary of Corominas says the origin is uncertain, but it suggests that it comes from the vulgar Latin cappula, plural of cappulum, sword hilt. According to Encarta Dictionary, the word cachalot came to English "via French from Spanish or Portuguese cachalote, perhaps from [Portuguese] cachola, 'big head'". The term is retained in the Russian word for the animal, кашалот (kashalot), as well as in many other languages.

Size
The sperm whale is the largest toothed whale, with adult males measuring up to 20.5 m long and weighing up to 57000 kg. By contrast, the second largest toothed whale, Baird's Beaked Whale measures 12.8 m and weighs up to 15 ST. The Nantucket Whaling Museum has a 5.5 m-long jawbone. The museum claims that this individual was 80 ft long; the whale that sank the Essex (one of the incidents behind Moby-Dick) was claimed to be 85 ft. However, there is disagreement on the claims of adult males approaching or exceeding 80 ft in length.

Extensive whaling may have decreased their size, as males were highly sought, primarily after World War II. Today, males do not usually exceed 18.3 m in length or 51000 kg in weight. However, contrary to this popular belief, expert T. Kasuya concluded through his study that exploitation by overfishing virtually had 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.

It is among the most sexually dimorphic of all cetaceans. At birth both sexes are about the same size, but mature males are typically 30% to 50% longer and three times as massive as females.

Appearance
The sperm whale's distinctive shape comes from its very large head, which is typically one-third of the animal's length. The 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. The whale lifts its flukes high out of the water as it begins a 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 knobbly and has been likened to a prune by whale-watching enthusiasts. Skin is normally a uniform grey in color, though it may appear brown in sunlight. Albinos have also been reported.

Jaws and teeth
The sperm whale has 20 to 26 teeth on each side of its lower jaw. The teeth are cone-shaped and weigh up to 1 kg. The purpose of the teeth is unknown. Teeth do not appear to be necessary for capturing or eating squid, and well-fed animals have been found without teeth. One hypothesis is that the teeth are used in aggression between males. Bulls often show scars which seem to be caused by the teeth. Rudimentary teeth are also present in the upper jaw, but these rarely emerge into the mouth.

Respiration and diving
Sperm whales, along with bottlenose whales and elephant seals, are the deepest-diving mammals. Sperm whales are believed to be able to reach 3 km and remain submerged for 90 minutes. More typical dives are around 400 m and 35 minutes in duration. At these great depths, sperm whales sometimes become entangled in transoceanic telephone cables and drown.

The sperm whale has adapted to cope with drastic pressure changes when diving. The flexible ribcage allows lung collapse, reducing nitrogen intake, and metabolism can decrease to conserve oxygen. Myoglobin, which stores oxygen in muscle tissue, is much more abundant than in terrestrial animals. The blood has a high red blood cell density, which contain oxygen-carrying hemoglobin. The oxygenated blood can be directed towards the brain and other essential organs only when oxygen levels deplete. The spermaceti organ may also play a role by adjusting buoyancy (see below).

While sperm whales are well adapted to diving, repeated dives to great depths have long term effects. Bones show pitting that signals decompression sickness in humans. Older skeletons showed the most extensive pitting, 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.

Between dives, the sperm whale surfaces to breathe for about eight minutes before diving again. Odontoceti (toothed whales) breathe air at the surface through a single, S-shaped blowhole. Sperm whales spout (breathe) 3–5 times per minute at rest, increasing to 6–7 times per minute after a dive. The blow is a noisy, single stream that rises up to 2 m or more above the surface and points forward and left at a 45° angle. On average, females and juveniles blow every 12.5 seconds before dives, while large males blow every 17.5 seconds before dives.

Brain and senses
The brain is the largest known of any modern or extinct animal, weighing on average about 8 kilograms (18 lb),, though the sperm whale has a lower encephalization quotient than many other whale and dolphin species, lower than that of non-human anthropoid apes, and much lower than humans'.

Like other toothed whales (suborder odontoceti), sperm whales use echolocation as one means to find food because their habitat has favorable acoustic characteristics, and light absorption by water and suspended material limits visual range. The whale emits a focused wide angle beam of high-frequency clicks. Passing air generates sounds from the bony nares through the phonic lips (also known as "monkey lips"), a structure within the head. The skull, melon, and various air sacs in the whale's head all play important roles in forming and focusing the beam of sound. The lower jaw is the primary echo reception path. A continuous fat-filled canal transmits received sounds to the inner ear.

Spermaceti functions
The spermaceti organs may help adjust the whale's buoyancy. Before the whale dives, cold water enters the organ, and it is likely that the blood vessels constrict, reducing blood flow, and, hence, temperature. The wax therefore solidifies. The increase in specific density generates a down force of about 392 N and allows the whale to dive with less effort. During the hunt, oxygen consumption, together with blood vessel dilation, produces heat and melts the spermaceti, increasing its buoyancy and enabling easy surfacing.

Herman Melville's Moby Dick suggests that the "case" containing the spermaceti 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 by attackers estimated to weigh only one-fifth as much as the ships.

The case may also aid echolocation (see melon). The organ's variable shape narrows or spreads the sound.

The sperm whale has two nostrils. An external nostril forms the blow hole, and an internal nostril presses against the bag-like spermaceti container. The male's spermaceti organ is much larger than the female's. This may be a case of sexual selection, enabling males to compete for females using sound displays.

Distribution
The sperm whale is among the most cosmopolitan species. It prefers ice-free waters over 1000 m deep. Although both sexes range through temperate and tropical oceans and seas, only adult males populate higher latitudes.

It is relatively abundant from the poles to the equator and is found in all the oceans. It inhabits the Mediterranean Sea, but not the Black Sea, while its presence in the Red Sea is uncertain. The shallow entrances to both the Black Sea and the Red Sea may account for their absence. The Black Sea's lower layers are also anoxic and contain high concentrations of sulphur compounds such as hydrogen sulphide.

Populations are denser close to continental shelves and canyons. Sperm whales are usually found in deep off-shore waters, but may be seen closer to shore in areas where the continental shelf is small and drops quickly to depths of 310 - 920 m. Coastal areas with significant sperm whale populations include the Azores and the Caribbean island of Dominica.

Reproduction


Sperm whales can live 70 years or more. They are a prime example of a species that has been K-selected, i.e., their reproductive strategy is associated with stable environmental conditions and comprises a low birth rate, significant parental aid to offspring, slow maturation, and high longevity.

How they choose mates has not been definitively determined. There is evidence that males have dominance hierarchies, and there is also evidence that female choice influences mating. Gestation requires 14 to 16 months, producing a single calf. Lactation proceeds for 19 to 42 months, but calves may suckle up to 13 years (although usually less). Calves can suckle from females other than their mothers. Females generally have birth intervals of three to six years.

Females reach sexual maturity between 7 and 13 years; males follow beginning at 18 years. Upon reaching sexual maturity, males move to higher latitudes, where the water is colder and feeding is more productive. Females remain at lower latitudes. Males reach their full size at about age 50.

Social behavior


Females stay in groups of about a dozen individuals and their young. Males leave these "nursery pods" at somewhere between 4 and 21 years of age and join a "bachelor pod" with other males of similar age and size. As males grow older, they tend to disperse into smaller groups, and the oldest males typically live solitary lives. Mature males have beached themselves together, suggesting a degree of cooperation which is not yet fully understood.

The most common non-human attacker of sperm whales is the orca, but pilot whales and the false killer whale also sometimes attack or harass them. Orcas target groups of females with young, usually trying to extract and kill a calf. Female sperm whales repel these attacks by encircling their calves. The adults either face inwards to use their tail flukes against the orcas, or outwards, fighting with their teeth. This marguerite formation, named after the flower, is also used by whales to support an injured pod member. Early whalers exploited this behaviour, attracting a whole pod by injuring one of its members. If the orca pod is extremely large, its members may sometimes be able to kill adult female sperm whales. Large bull sperm whales have no non-human predators, and are believed to be too large and strong to be threatened by orcas.

Feeding


Sperm Whales usually dive between 300 to 800 m, and sometimes 1 - 2 km to search for food. Such dives can last more than an hour. They feed on several species, notably the giant squid, the colossal squid, octopuses, and diverse fish like demersal rays, but the main part of their diet consists of medium-sized squid. Some prey may be taken incidentally while eating other items. Most of what is known about deep sea squid has been learned from specimens in captured sperm whale stomachs, although more recent studies analysed fecal matter. One study, carried out around the Galápagos, found that squid from the genera Histioteuthis (62%), Ancistrocheirus (16%), and Octopoteuthis (7%) weighing between 12 and 650 g were the most commonly taken. Battles between sperm whales and colossal squid (which have been measured to weigh nearly 500 kg) have never been observed by humans; however white scars are believed to be caused by the large squid. One study published in 2010 collected evidence that suggests that female sperm whales may collaborate when hunting Humboldt squid.

An older study, examining whales captured by the New Zealand whaling fleet in the Cook Strait region, found a 1.69:1 ratio of squid to fish by weight. Sperm whales sometimes steal Sablefish and Toothfish from long lines. Long-line fishing operations in the Gulf of Alaska complain that sperm whales take advantage of their fishing operations to eat desirable species straight off the line, sparing the whales the need to hunt. However, the amount of fish taken is very little compared to what the sperm whale needs per day. Video footage has been captured of a large male sperm whale "bouncing" a long line, to gain the fish. Sperm whales are believed to prey on the megamouth shark, a rare and large deep-sea species discovered in the 1970s. In one case, three sperm whales were observed attacking or playing with a megamouth.

The sharp beak of a consumed squid lodged in the whale's intestine may lead to the production of ambergris, analogous to the production of pearls. The irritation of the intestines caused by squid beaks stimulates the secretion of this lubricant-like substance. Sperm whales are prodigious feeders and eat around 3% of their body weight per day. The total annual consumption of prey by sperm whales worldwide is estimated to be about 100000000 ST — a figure greater than the total consumption of marine animals by humans each year.

It is not well understood why the sperm whale's head is so large in comparison to the lower jaw. One theory is that the sperm whale's ability to echolocate through its head aids in hunting. However squid, its main prey, may have acoustic properties too similar to seawater to reflect sounds. The sperm whale's head contains a structure called monkey lips, through which it blows air. This can create clicks that have a source level exceeding 230 decibels re 1 micropascal referenced to a distance of 1 m – in other words it is by far the loudest sound made by any animal, and 10–14 dB louder than a powerful rifle sounds in air at 1 m away. It has been hypothesised that clicks attempt to stun prey. Experimental studies attempting to duplicate this effect have been unable to replicate the supposed injuries, casting doubt on this idea.

Taxonomy and naming
The sperm whale belongs to the order Cetacea, the order containing all whales and dolphins. It is a member of the suborder Odontoceti, the suborder 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. simus, are either placed in this family, or in the family Kogiidae. In some taxonomic schemes the families Kogiidae and Physeteridae are combined as the superfamily Physeteroidea (see the separate entry on the sperm whale family).

The sperm whale is one of the species originally described by Linnaeus in 1758 in his 18th century work, 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's status to a lesser synonym.

Fossil record
Although the fossil record is poor, several extinct genera have been assigned to the clade Physeteroidea, which includes the last common ancestor of the modern sperm whale, pygmy sperm whale and dwarf sperm whale, plus all of that ancestor's descendants. These fossils include Ferecetotherium, Idiorophus, Diaphorocetus, Aulophyseter, Orycterocetus, Scaldicetus, Placoziphius, Zygophyseter and Acrophyseter. Ferecetotherium, found in Azerbaijan and dated to the late Oligocene (about ), is the most primitive fossil that has been found which possesses sperm whale-specific features such as an asymmetric rostrum ("beak" or "snout"). Most sperm whale fossils date from the Miocene period,. Diaphorocetus, from Argentina, has been dated to the early Miocene. Fossil sperm whales from the Middle Miocene include Aulophyseter, Idiorophus and Orycterocetus, all of which were found on the west coast of the United States, and Scaldicetus, found in Europe and Japan. Orycterocetus fossils have also been found in the North Atlantic Ocean and the Mediterranean Sea, in addition to the west coast of the United States. Placoziphius, found in Europe, and Acrophyseter, from Peru, are dated to the late Miocene.

Evolutionary family tree of sperm whales, including simplified summary of extinct groups (†) Fossil sperm whales differ from modern sperm whales in tooth count and the shape of the face and jaws. For example Scaldicetus had a tapered rostrum. Genera from the Oligocene and early and middle Miocene, with the possible exception of Aulophyseter, had teeth in their upper jaws. Acrophyseter, from the late Miocene, also had teeth in both the upper and lower jaws as well as a short rostrum and an upward curving mandible (lower jaw). These anatomical differences suggest that fossil species may not have necessarily been deep-sea squid eaters like the modern sperm whale, but that some genera mainly ate fish. Zygophyseter, dated from the middle to late Miocene and found in southern Italy, had teeth in both jaws and appears to have been adapted to feed on large prey, rather like the modern Orca (Killer Whale).

Phylogeny
The traditional view has been that Mysticeti (baleen whales) and Odontoceti (toothed whales) arose from more primitive whales early in the Oligocene period, and that the super-family Physeteroidea, which contains the sperm whale, dwarf sperm whale, and pygmy sperm whale, diverged from other toothed whales soon after that, over. In 1993–1996 molecular phylogenetics analyses by Milinkovitch and colleagues, based on comparing the genes of various modern whales, suggested that the sperm whales are more closely related to the baleen whales than they are to other toothed whales, which would have meant that Odontoceti were not monophyletic, in other words did not consist of a single ancestral toothed whale species and all its descendants. However more recent studies, based on various combinations of comparative anatomy and molecular phylogenetics, criticised Milinkovitch's analysis on technical grounds and re-affirmed that the Odontoceti are monophyletic.

These analyses also confirm that there was a rapid evolutionary radiation (diversification) of the Physeteroidea in the Miocene period. The Kogiidae (dwarf and pygmy sperm whales) diverged from the Physeteridae (true sperm whales) at least.

Cultural importance
Rope-mounted teeth are important cultural objects throughout the Pacific. In New Zealand, the Māori know them as "rei puta" and were rare because sperm whales were not actively hunted in traditional Māori society. Whale ivory and bone were taken from beached whales. In Fiji the teeth are known as tabua and they were traditionally given as gifts for atonement or esteem (called sevusevu), and were important in negotiations between rival chiefs. Friedrich Ratzel in The History of Mankind reported in 1896 that, in Fiji, whales' or cachalots' teeth were the most-demanded article of ornament or value. They occurred often in necklaces. Today the tabua remains an important item in Fijian life. The teeth were originally rare in Fiji and Tonga, which exported teeth, but with the Europeans' arrival, teeth flooded the market and this "currency" collapsed. The oversupply led in turn to the development of the European art of scrimshaw.

Herman Melville's novel Moby-Dick is based on a true story about a sperm whale that attacked the whaleship Essex. Melville associated the sperm whale with the Bible's Leviathan. The fearsome reputation perpetuated by Melville was based on bull whales' ability to fiercely defend themselves from attacks by early whalers, occasionally resulting in the destruction of the whaling ships.

Jules Verne's Twenty Thousand Leagues Under the Sea, mentions cachalots (perhaps incorrectly) as preying on fellow whales.

The Sperm Whale was designated as the Connecticut state animal by the CT General Assembly in 1975. It was selected because of its specific contribution to the state's history and because of its present-day plight as an endangered species.



Watching sperm whales
Sperm whales are not the easiest of whales to watch, due to their long dive times and ability to travel long distances underwater. However, due to the distinctive look and large size of the whale, watching is increasingly popular. Sperm whale watchers often use hydrophones to listen to the clicks of the whales and locate them before they surface. Popular locations for sperm whale watching include the picturesque Kaikoura on New Zealand's South Island, where the continental shelf is so narrow that whales can be observed from the shore, Andenes and Tromsø in Arctic Norway and at the Azores where it can be seen throughout the year. Dominica is believed to be the only Caribbean island with a year-round residential pod of females and calves.