The sperm whale (Physeter macrocephalus) is a species of whale found in the disphotic, and aphotic zones and it migrates to the euphotic zone for feeding. It is the largest of the toothed whales and the largest toothed predator. It is the only living member of genus Physeter and one of three living species in the sperm whale family, along with the pygmy sperm whale and dwarf sperm whale of the genus Kogia.
The sperm whale’s distinctive shape comes from its very large, block-shaped head, which can be one-quarter to one-third of the animal’s length. The S-shaped blowhole is located very close to the front of the head. This gives rise to a distinctive bushy, forward-angled spray. The sperm whale’s tail lobes are triangular and very thick. Proportionally, they are larger than that of any other cetacean and are very flexible. The whale lifts its tail lobes high out of the water as it begins a feeding 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.
The sperm whale respiratory system 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. 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, which is extremely skewed to the left. 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 metres (6.6 ft) 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. A sperm whale killed 160 km (100 mi) south of Durban, South Africa after a 1-hour, 50-minute dive was found with two dogfish (Scymnodon sp.), usually found at the sea floor, in its belly.
The sperm whale has the longest intestinal system in the world, exceeding 300 m in larger specimens. Similar to ruminants the sperm whale has a four-chambered stomach. The first secretes no intestinal juices and has very thick muscular walls to crush the food since whales cannot chew, and resist the claw and sucker attacks of swallowed squid.
The second chamber is larger and is where digestion takes place. Undigested squid beaks accumulate in the second chamber – as many as 18,000 have been found in some dissected specimens.
Most squid beaks are vomited by the whale, but some occasionally make it to the hindgut. Such beaks precipitate the formation of ambergris.
The brain is the largest known of any modern or extinct animal, weighing on average about 7.8 kilograms, more than five times heavier than a human’s. Although larger brains generally correlate with higher intelligence, it is not the only factor. Elephants and dolphins also have larger brains than humans. The sperm whale has a lower encephalization quotient than many other whale and dolphin species, lower than that of non-human apes, and much lower than humans.
The sperm whale’s cerebrum is the largest in all mammals, both in absolute and relative terms. The olfactory system is reduced, suggesting that the sperm whale has a poor sense of taste and smell. By contrast, the auditory system is enlarged. The pyramidal tract is poorly developed, reflecting the reduction of its limbs.
Spermaceti oil (called “sperm” for short), from which the whale derives its name, was a prime target of the whaling industry, and was dominant for use in oil lamps, lubricants, and candles. Ambergris is a solid waxy waste product from its digestive system. It is still highly valued as a fixative in perfumes and other uses. It remains as flotsam from deceased whales, and is sought by beachcombers. The species is now protected by a whaling moratorium, and is currently listed as vulnerable by the International Union for Conservation of Nature (IUCN).