This site is indebted to the writings of Lyall Watson (amongst others), for his amazing and well-researched book Whales of the World, illustrated by Tom Ritchie.

The Sperm Whale (Physeter macrocephalus)

is the largest of all toothed whales and is believed to be the largest toothed animal to ever inhabit Earth, measuring up to 18 m (60 ft) long. (The baleen blue whale is larger, and invertebrates such as the lion's mane jelly fish or the Portuguese man of war may be longer.) 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 mythological Leviathan of Biblical lore.

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 Azores.
The Sperm Whale is exceptional for its very large head, particularly in males, which is typically one-third of the animals' length. Indeed, the species name macrocephalus is derived from the Greek for "big head" (strictly: long 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 [1]. 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, and white sperm whales have been reported in reality as well). 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 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 (16–18 m, 52-59 ft) than females (12–14 m, 39-46 ft) and weigh about twice as much (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 1,000 kg (1 tonne) in weight. Due 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, weighing around 150 metric tons (165 short tons). Another evidence of large bulls of the past resides in New Bedford museum, a 5.2 meters (17 feet) jaw of a bull that could have been about 25.6 meters (84 feet) long, weighing 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 average 18 m (60 feet) in length and 52 metric tons (57 short tons) in weight.Sperm whale herds appear to be organized on a "harem" system similar to elephants where a solitary bull (male) sperm whale joins a school of 10-40 adult females plus their calves, and juveniles (of both sexes) for the length of a breeding season.   Males sometimes fight to gain control of harems by biting and butting of other males.  Females will sometimes assist this process by driving away older males. 

Breeding seasons occur in the middle of summer according to hemisphere and 12-13 foot calves are born after a 14-16 month gestation period.   Females nurse their calves for two years and longer suggesting that nursing is both a social and a feeding function for sperm whales.  Females are able to conceive at about 28 feet (8.5 meters) long, while male sperm whales are probably not able to mate until they are 39 feet (11.9 meters) long. 

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.

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.
Sperm Whales, along with bottlenose whales, are the deepest-diving mammals in the world. They are believed to be able to dive up to 3,000 metres in depth and 2 hours in duration to the ocean floor. More typical dives are around 400 metres in depth and 30–45 minutes' duration. They feed on several species, in particular giant squid, octopuses and demersal rays. Almost all that is known about deep sea squid has been learned from specimens found in captured Sperm Whale stomachs. Stories about titanic battles between Sperm Whales and giant squid which are believed to reach up to 13 m (44 ft) are perhaps the stuff of legend. However, white scars on the bodies of Sperm Whales are believed to be caused by squid. It is also 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. 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 comparable with the total consumption of marine animals by humans each year.

In addition, 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 [8].

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.

The social structure of the Sperm Whales species divides on sexual lines. Females are extremely social animals, a trait believed to derive from their relatively simple evolutionary path. 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.