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Sperm Whale


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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 60 ft (18 m) long. (The baleen blue whale is larger, and invertebrates such as the Lion's Mane Jellyfish 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. Historically the Sperm Whale has also been known as the Common Cachalot. The word cachalot is originally Portuguese (cachalote), probably coming from cachola, and a colloquial term for head. Sperm Whales were hunted until recently in the Portuguese Atlantic archipelago of Azores.

Physical description

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 knobby and has been likened to a prune by whale-watching enthusiasts. They are uniformly grey in color though may appear brown in sunlight. Perhaps unsurprisingly, the brain of the Sperm Whale is the largest and heaviest known of any modern or extinct animal (weighing on average 15 lb (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 whales 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 and indeed healthy well-fed Sperm Whales have been found in the wild without teeth.

Male and female Sperm Whales differ the most of all the cetaceans. Males are typically 30%–50% longer (52-59 ft , 16–18 m) than females (39-46 ft , 12–14 m) and weigh about twice as much (55 short tons vs. 27.5 short tons, 50,000 kg vs. 25,000 kg). At birth both males and females are about 13 feet (4 m) in length and 1 ton (1,000 kg) in weight. Due to extensive whaling, Sperm Whale size has decreased dramatically, mostly because the largest males were killed first.

Taxonomy

The Sperm Whale was categorized first by Linnaeus in 1758 that recognized four species in the Physeter genus. Experts soon realized that just one such species exists. In most modern publications the Sperm Whale is classified as the sole species in the family Physeteridae (and thus the only species in its genus). The sperm whale family is sometimes treated as a super family, Physeteroidea. This super family contains only two other species—the Pygmy Sperm Whale and the Dwarf Sperm Whale. These two whales belong to the family Kogiidae.

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

Feeding, behavior and diving

Sperm Whales, along with bottlenose whales, are the deepest-diving mammals in the world. They are believed to be able to dive up to 1.6 miles (3,000 meters) in depth and 2 hours in duration to the ocean floor. More typical dives are around 1/3 mile (400 meters) 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 that are believed to reach up to 44 ft (13 m) 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 hypothesized 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 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.

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 breathe 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.

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 denser close to continental shelves and canyons, probably because of easier feeding. Sperm Whales are usually found in deep offshore waters, but may be seen closer to shore in areas where the continental shelf is small.

Population and hunting

The total 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 (used as a lubricant in machinery) and spermaceti (used in candles), 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.

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