Sperm Whale
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[Photo] Scarred Giant (detail)??? Artist: Chris Harman. Source: http://www.velvetgreencreations.com/Marinelife/marinlife.html

The Sperm Whale (Physeter macrocephalus) is the largest of all toothed whales and is the largest toothed animal alive, measuring up to 18 metres (60 ft) long. The whale was named after the milky-white waxy 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 because of Melville, the Sperm Whale is commonly associated with the Leviathan of the Bible.

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 hunted until recently in the Portuguese Atlantic archipelago of the Azores. The Sperm Whale is also the state animal of Connecticut.

Description
The Sperm Whale is exceptional for its very large head, particularly in males, which is typically one-third of the animal's 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. They are uniformly grey in colour, though they may appear brown in sunlight; white albino whales have also been reported. Perhaps unsurprisingly, the brain of the Sperm Whale is the largest and heaviest known of any modern or extinct animal (weighing on average 7 kg (15 lb) 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 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 amongst the most sexually dimorphic (that is, males and females differ greatly) of all cetaceans. Males are typically 30% to 50% longer (16-18 m, 52???59 ft) than females (12-14 m, 39???46 ft) and are twice as massive (50 000 kg vs. 25 000 kg, 55 short tons vs 27.5 short tons). At birth both males and females are about 4 m (13 feet) in length and mass of 1 000 kg (1 tonne).

Owing to extensive whaling, Sperm Whale size has decreased dramatically, mostly because the largest males were killed first and most intensively, for they had more spermaceti (spermaceti oil was of great value in the 18th and 19th century - see below). In a Nantucket museum there is a jawbone of a sperm whale which is 5.5 m (18 ft). The jawbone makes up to 20%-25% of the sperm whale's overall body length. Thus this whale might have been 28 m (90 ft) long, a mass of around 150 metric tons (165 short tons). Another evidence of large bulls of the past resides in New Bedford museum, a 5.2 metres (17 ft) jaw of a bull that could have been about 25.6 metres (84 feet) long, with a mass of about 120???130 tons. In addition, log books found in the Nantucket and 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. 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.

Sperm Whales are a prime example of a species that has been K-selected, which is to say that the species is believed to have developed primarily under very stable environmental conditions. 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.

The Sperm Whale holds some natural world records:

Largest known toothed mammal ever.
Largest brain of any living creature on Earth. The brain of a mature sperm whale weighs 7 kg (15 pounds), though there have been specimens with 9 kg (20 pound) brains.
Largest living carnivore on Earth.
Deepest diving mammal (found at depths of 2,200 meters (7,200 feet) and can hold its breath for up to 2 hours.
Loudest animal in the world. Sperm whale clicks have a source level exceeding 230 dB re 1 micropascal referenced to a distance of 1 metre.

In 1820, a sperm whale estimated to be about 25.9 m (85 ft) long attacked a Nantucket whaling ship Essex. Only 8 out of the 20 sailors managed to survive and be rescued by other ships.

According to a 2003 National Geographic article, Sperm Whales are said to be the loudest of all animals ("about as loud as a rifle shot three feet from your ear").

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. The substance is not, of course, the whale's semen, but 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, 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.

A theory pertaining to the echolocation abilities of these animals holds that the combination of the shape of the whale's skull, the highly variable geometry (in three dimensions) of the muscle-sheathed spermaceti container, and the presence of this "internal nostril" may endow the sperm whale with astounding powers of sound production - not only being able to echolocate with high fidelity, but to produce other effects with sound waves/ mechanical energy as well. For example, it is postulated that sperm whales, ungainly and ponderous swimmers, may need "something extra" to capture the agile-swimming squid they eat, and the ability to stun or even kill such prey with a burst of sound would "fit the bill". However, so far, this hypothesis remains only an intriguing theory.

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 photographic lenses and delicate high-altitude instruments, cosmetics, additives in motor oils, glycerine, rust-proofing compounds, detergent, chemical fibres, vitamins and 70 or more pharmaceutical compounds.

Spouting, and breathing
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. They 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.

Ecology, behaviour and life history

Feeding, behaviour and diving
Sperm Whales, along with bottlenose whales and elephant seals, are the deepest-diving mammals in the world.

They 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 400 m (437 yards) in depth and 30???45 minutes' duration and generally move in a northerly direction. They can dive two miles deep with one gulp of air for two hours. They carry three tonnes of blood which holds enough oxygen to help it achieve its diving depth.

They feed on several species, in particular giant squid, octopuses and diverse fish like demersal rays, but the main part of their diet consists of medium sized squid. Almost all that is known about deep sea squid has been learned from specimens found in captured Sperm Whale stomachs.

Giant squid are considered to be the sperm whale's prime diet, as large deep sea fish stocks are becoming depleted by humans. Stealing of Sablefish and Toothfish from long lines has been documented and well known also. It is believed that this trait is learned and passed on to other whales within the pod or offspring. Titanic battles between Sperm Whales and Colossal Squid, which can reach up to 14 m (46 ft), have never been observed by humans. However, white scars on the bodies of Sperm Whales are believed to be caused by squid.

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.

The only predator that attacks Sperm Whales, besides human beings, is the Orca. Large, roving pods of 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 and then violently thrashing their tail flukes, so that no Orca can penetrate the formation. If the Orca pod is extremely large, they may sometimes also kill adult females. Large bull Sperm Whales have no predators, as even Orcas could be killed by these aggressive, powerful creatures.

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.

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).

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 for breath and remain more or less still for eight to ten minutes before diving again.

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

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.

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.

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