Common Cachalot

Sperm Whale

The Sperm Whale (Physeter macrocephalus or Physeter catodon) is the largest of all toothed whales and largest living toothed animal. The whale was named after the milky-white waxy substance, spermaceti, found in its head and originally mistaken for sperm. It has a cosmopolitan distribution across the world's oceans. The species feeds on squid and fish, diving as deep as in order to obtain its prey, making it the deepest diving mammal in the world. Pods of females and young live separately from older males. Sperm whales live for more than 70 years.

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 because of Melville, the Sperm Whale is commonly associated with the Leviathan of the Bible. The fearsome reputation perpetuated by Melville was based on bull whales' ability to fiercely defend themselves from attacks by early whalers, sometimes resulting in the destruction of the whaling ships. Historically the Sperm Whale has also been known as the common cachalot. The word cachalot is originally Portuguese (cachalote), probably coming from cachola, a colloquial term for head. Sperm whales were commercially hunted until recently, declined as a consequence of over-harvesting, and are currently listed as vulnerable by the IUCN.

Description

Sperm whales are the largest toothed whales, with adult males measuring up to long. Their distinctive shape comes from their very large head, particularly in males, which is typically one-third of the animal's length. 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. They are uniformly grey in colour, though they may appear brown in sunlight; white albino whales have also been reported. The brain of the Sperm Whale is the largest and heaviest known of any modern or extinct animal (weighing on average in a grown male). However, proportionally, the brain's weight is less than half that of a human brain when body size is factored in.

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 blow angled forward. The Sperm Whale has no true dorsal fin, instead a series of ridges are present on the caudal third of the back. The largest was called the 'hump' by whalers and is commonly mistaken for a dorsal fin because of its shape.

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 8–20 cm (3–8 in) long. 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 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. Furthermore bull Sperm Whales often show scars which seem to be caused by the teeth of other bulls. Rudimentary teeth are also present in the upper jaw, but these rarely open into the mouth.

Sperm whales are among the most sexually dimorphic (that is, males and females differ greatly) of all cetaceans. Males are typically 30% to 50% longer (approximately ) than females (approximately ) and are three times as massive (41 000 kg vs. 14 000 kg, 45 short tons vs 15 short tons). At birth both males and females are about 4 m (13 ft) in length, with a mass of 1 000 kg (1 tonne).

The largest bull Sperm Whale verified and accurately measured was 20.5 m (67.9 ft) and 80 tonnes (88 tons). However, there is evidence of larger bulls than this. Owing to extensive whaling, Sperm Whale size may have decreased, as males were heavily exploited during the modern era, primarily after World War II. In a Nantucket museum there is a jawbone of a Sperm Whale which is 5.5 m (18 ft). The jawbone makes up 25% of the Sperm Whale's overall body length. Thus this whale might have been at most 23 m (72 ft) long, a mass of around 105 metric tons (118 short tons). Further evidence of larger bulls in the past resides in New Bedford museum, a 5.2 metres (17 ft) jaw of a bull that could have been about 21.7 metres (68 ft) long, with a maximum mass of about 100 tons. In addition, logbooks found in the Nantucket and New Bedford museums are filled with references to bulls that were, considering the amount of oil they yielded, about the same size as these two examples- although whalers were notorious for exaggerating the yield of oil and length of whales they caught. Today, Sperm Whale males do not usually exceed 18 m (60 ft) in length and 52 metric tons (57 short tons). The largest Sperm Whales observed are comparable in size to the fin whale (and smaller than blue whales), making the Sperm Whale either the second or third largest animal species alive.

Spermaceti

Spermaceti is the semiliquid, waxy substance found in the head of the Sperm Whale. The name derives from the late Latin sperma ceti (both words actually loaned 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. Early beach-combers mistook the substance for the whale's semen. 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, waxy substance saturated with spermaceti. The junk is a more solid substance.

One function of the spermaceti organs is a buoyancy or diving organ. Before diving, cold water is brought through the organ and the wax is solidified. The increase in specific density generates a down force (approx 40 kg equiv) and allows the whale effortless sinking. During the chase in deep levels (max 3,000m) the stored oxygen is consumed and excess heat melts the spermaceti. Now only hydrodynamic forces (by swimming) keep the whale down before effortlessly surfacing.

Hypotheses on further functions exist: One 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.

Another possibility is that the case is used as an aid to echolocation (see melon). The shape of the organ at any given time is likely to focus or widen the beam of emitted sound. The Sperm Whale actually has two nostrils — one external nostril, forming the blow hole, and one internal nostril pressing against the bag-like spermaceti container.

Spermaceti was much sought after by 18th, 19th and 20th century whalers. The substance found a variety of commercial applications, such as candles, soap, cosmetics, machine oil, other specialized lubricants, lamp oil, pencils, crayons, leather waterproofing, rust-proofing materials and many pharmaceutical compounds.

Distribution

The Sperm Whale is among the most cosmopolitan species in the world, and is found in all the oceans and the Mediterranean Sea. The species is relatively abundant from Arctic waters to the equator. Populations are more dense close to continental shelves and canyons, probably because of easier feeding. 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, dropping quickly to 1,000 to 3,000 feet deep. Examples of areas close to the shore with significant Sperm Whale populations include the Azores and the Caribbean island of Dominica.

Ecology, behaviour and life history

Sperm whales are a prime example of a species that has been K-selected, a reproductive strategy associated with very stable environmental conditions that is characterized by a low birth rate, significant parental aid to offspring, slow maturation and high longevity. Females give birth once every four to six years, and the gestation period is between 14 and 16 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 can live for more than 70 years.

The social structure of the Sperm Whales species divides on sexual lines. Females are extremely social animals. Females stay in groups of about a dozen individuals and their young. Males leave these "nursery schools" at somewhere between 4 and 21 years of age and join a "bachelor school" with other males of a similar age and size. As males grow older, they tend to disperse into smaller groups, and the oldest males typically live solitary lives. Yet mature males have been stranded on beaches together, suggesting a degree of co-operation not yet fully understood.

Few predators besides humans attack Sperm Whales. The most common attacker of Sperm Whales is the Orca, but pilot whales and the False Killer Whale also sometimes attack or harass Sperm Whales. Pods of transient Orcas frequently target groups of females with young, usually trying to separate the Sperm Whale calf and kill it. Often, the female Sperm Whales can repel these attacks by forming a circle with their calves in the centre. The adults either face inside the circle, in which case their tail flukes can be used to defend against the Orcas, or they face outside the circle, in which case their jaws are the principal defensive weapons. If the Orca pod is extremely large, they may sometimes also kill adult females. Large bull Sperm Whales have no non-human predators, as even Orcas could be killed by these aggressive, powerful creatures.

Feeding

Sperm whales feed on several species, notably the Giant Squid, the Colossal Squid, krill, octopuss, and diverse fish like demersal rays, but the main part of their diet consists of medium sized squid. Most of what is known about deep sea squid has been learned from specimens found in captured Sperm Whale stomachs, although more recent studies have analysed fecal matter instead. One study, carried out around the Galápagos, found that squid from the genera Histioteutbis (62%), Ancistrocbeirus (16%), and Octopoteutbis (7%) were the most commonly taken, and that most squid were between 12-650 kg in weight. An older study, examining the contents of 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. Stealing of Sablefish and Toothfish from long lines has been documented and well known also (see below). 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 on the bodies of Sperm Whales are believed to be caused by squid. In one case three Sperm Whales were observed attacking or playing with a megamouth shark, a rare and large deep-sea species only discovered by man in the 1970s.

It is hypothesised that the sharp beak of a consumed squid lodged in the whale's intestine leads to the production of ambergris, analogous to the production of pearls. The irritation of the intestines caused by the 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 100 million tons — a figure greater than the total consumption of marine animals by humans each year.

It is difficult to see why the Sperm Whale has such a large head in comparison to the lower jaw. One theory explaining this is that the Sperm Whale's ability to echolocate through its head aids in hunting. Within the head, it contains a structure called monkey lips, which it blows air through. This can create clicks that have a source level exceeding 230 dB re 1 micropascal referenced to a distance of 1 metre. It has been hypothesised that these were directed at prey in order to stun them, however experimental studies attempting to duplicate this effect have been unable to replicate the supposed injuries, and have cast doubt on this idea.

Long-line fishing operations in the Gulf of Alaska have complained that numerous Sperm Whales have taken advantage of their fishing operations to eat desirable species straight off the line, sparing the whales the need to hunt them themselves. However, the amount of fish taken is very little compared to what the Sperm Whale needs per day. New video footage has been captured of a large male Sperm Whale "bouncing" a long line, to gain the fish.

Diving and breathing

Sperm whales, along with bottlenose whales and elephant seals, are the deepest-diving mammals in the world. Sperm whales are believed to be able to dive up to 3 km (1.9 miles) in depth and 90 minutes in duration to the ocean floor. More typical dives are around in depth and 35 minutes in duration. They carry three tonnes of blood which holds enough oxygen to help it achieve its diving depth.

The physiology of the Sperm Whale has several adaptations to cope with drastic changes in pressure when diving. The ribcage is flexible to allow lung collapse, and the heart rate can decrease to preserve oxygen supplies. Myoglobin stores oxygen in muscle tissue. Blood can be directed towards the brain and other essential organs only, when oxygen levels deplete. The spermaceti organ may also play a role (see above).

Because of the great depths to which they dive, Sperm Whales sometimes drown when entangled in transoceanic telephone cables.

While Sperm Whales are well adapted to diving, repeated dives to great depths do have long term effects on the whales. Skeletons of Sperm Whales show pitting of the bones that is often a sign of decompression sickness in humans. Skeletons of the oldest whales showed the most extensive pitting, whereas skeletons of Sperm Whale 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 will come up to the surface to breathe for about eight minutes before diving again. Odontoceti (toothed whales) breathe air at the surface of the water through a single, s-shaped blowhole. The blowhole is located on the left side of the front of the head. Sperm whales spout (breathe) 3–5 times per minute at rest, but the rate increases to 6–7 times per minute after a dive. The blow is a noisy, single stream that rises up to 15 m (50 ft) above the surface of the water and points forward and to the left of the whale at a 45° angle. On average, females and immatures blow every 12.5 seconds before dives, while large males blow every 17.5 seconds before dives.

Taxonomy and naming

The Sperm Whale is one of the many 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 its correct name is a matter of dispute (see below). However, most scientists, the International Code for Zoological Nomenclature, and the International Whaling Commission prefer P. macrocephalus over P. catodon.

The Sperm Whale is the sole extant species of its genus, Physeter, which is placed 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 sometimes also placed in this family, or else are placed in their own family, Kogiidae.

The correct scientific name for the Sperm Whale is currently unclear. Until 1974 the species was generally known as P. catodon, however in that year Husson & Holthuis proposed that the correct name should be P. macrocephalus, the second name in the genus Physeter published by Linnaeus concurrently with P. catodon, on the grounds that the names were synonyms published simultaneously and therefore the ICZN principle of "First Reviser" should apply, in this instance leading to the choice of P. macrocephalus over P. catodon, a view re-stated in Holthuis, 1987. This has been adopted by some subsequent authors, however Schevill (1986 and 1987) 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. At the present time, the name P. catodon is used in the most high profile species information systems, for example the Catalogue of Life and the World Register of Marine Species, however some other sources use P. macrocephalus, for example in the IUCN Red List of Threatened Species and in various papers and book chapters, e.g. Whitehead, 2002; therefore, to retrieve maximum relevant information, it is currently advisable to search under both names. According to the relevant species page on ITIS, the Integrated Taxonomic Information System, "Physeter catodon and Physeter macrocephalus are awaiting a ruling regarding their usage by the ICZN".

The following is an extract from Melville's Moby-Dick, in which he expatiates about the vernacular naming and common lore surrounding the Sperm Whale:

Evolution

Sperm whales are believed to have diverged from other toothed whales early in the evolution of the suborder—around 20 million years ago, and a number of fossil genera and species have been described from the Late Oligocene period and beyond (refer main article Sperm whale family).

Relationship with humans

Cultural importance

The teeth of Sperm Whales, when mounted on rope, are important cultural objects in Fiji, where they are known as tabua. They were traditionally given as gifts for atonement or esteem (called sevusevu), and were important in negotiations between rival chiefs. Today the tabua remains an important item in Fijian life. The teeth were originally rare in Fiji and Tonga (which exported the teeth), however with the arrival of Europeans the market was flooded with teeth, so many that it collapsed. The oversupply led in turn to the development of the European art of scrimshaw.

The Sperm Whale is also the state animal of Connecticut.

Population and hunting

The number of Sperm Whales throughout the world is unknown. Crude estimates, obtained by surveying small areas and extrapolating the result to all the world's oceans, range from 200,000 to 2,000,000 individuals. Although the Sperm Whale was hunted for several centuries for its meat, oil and spermaceti, the conservational outlook for Sperm Whales is brighter than that for many other whales. Although a small-scale coastal fishery still occurs in Indonesia, they are protected practically worldwide. Fishermen do not catch the deep-sea creatures that Sperm Whales eat, and the deep sea is likely to be more resistant to pollution than surface layers.

In June 1821, a Sperm Whale claimed to be about 25.9 m (85 ft) long attacked the Nantucket whaleship Essex. Only 8 out of the 21 sailors managed to survive and be rescued by other ships.

However, the recovery from the whaling years is a slow process, particularly in the South Pacific, where the toll on males of a breeding age was severe.

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.

In the news

In July 2003 a huge blob of white flesh was found washed up on a beach on the coast of southern Chile. The 12-metre (40 ft) long mass of gelatinous tissue gave rise to speculation that a previously unknown giant octopus had been discovered. However, researchers at the Museum of Natural History, Santiago concluded that the mass was in fact the innards of a Sperm Whale, a conclusion drawn by looking at the dermal glands. When a Sperm Whale dies, its internal organs rot, until the animal becomes little more than a semi-liquid mass trapped inside the skin. Eventually, the skin will burst, causing the internal mass to float free and possibly wash up on the beach.

Dead Sperm Whales float towards shore quite often. Apart from the disposal issues identified above, beach managers fear that sharks, in particular the great white shark, will be attracted towards the beach by the rotting flesh, and potentially cause danger to beach users. For this reason, dead Sperm Whales are often towed out to sea before they become properly beached. This occurred twice in May 2004, once off Oahu in Hawaii where a dead whale was towed out to sea but floated back to shore two days later.

Exploding whales

Perhaps the most famous piece of Sperm Whale lore dates from 1970, when a long-dead, 8 short ton (7.25 tonne), 45 foot (13.7 m) long specimen came to a beach in Oregon. For a time, it was a curiosity to local residents. As the beach is public right-of-way, it was the duty of the Oregon Department of Transportation to dispose of it. They filled the animal with a half-ton of dynamite. On Thursday, November 12, the dynamite was set off, but the blast did not go toward the Pacific as planned. No one was hurt, but a car was crushed by falling blubber. Onlookers were covered with noxious-smelling bits of dead whale.

January 2004 saw a more dramatic entry of the Sperm Whale into the global media spotlight. A dead specimen of the whale, 17 metres long and weighing 50 tonnes, had washed up on a local beach in Tainan City, Taiwan. On being transported to a university in the city, gas pressure from decomposition built up inside the body, causing an explosion. Nobody was hurt, but blood and entrails were spread over several cars and surrounding pedestrians.

Accidents

In March 2007, a Japanese fisherman drowned after his boat was capsized by a panicked Sperm Whale he was trying to rescue. The whale had wandered into the relatively shallow waters in a bay in Shikoku.

Bibliography

References

External links

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