Physeteridae: Sperm Whale Family
There are 3 species of sperm whale, 1 of which is the largest of all toothed whales, while the other 2 are among the smallest whales. Their characteristic feature is the spermaceti organ, located in the space above the toothless upper jaw; this contains a liquid, waxy substance which may be involved in controlling buoyancy when the whale makes deep dives. All sperm whales have underslung lower jaws but have little else in common.
Sperm whales are supremely well adapted to life in the deep oceans. These are the largest hunting predators in the world, with teeth up to 20 cm (8 in) long and the largest brains of any mammal, weighing over 9 kg (20 lb). They prefer areas of ocean with cold upwellings at least 1,000 m (3,300 ft) deep, where squid - their favourite food - are most abundant.
The largest of the toothed whales, the sperm whale has a huge head, as great as one-third of its total body length, and a disproportionately small lower jaw, set well back from the snout. On its back is a fleshy hump and behind this are several smaller humps. Its flippers are short, but the tail is large and powerful and useful for acceleration. Surrounding the nasal passages in the huge snout is a mass of the waxy substance known as spermaceti. When the whale dives, it allows these passages to fill with water and by controlling the amount and temperature of the water taken in at different depths, it can alter the density of the wax and thus the buoyancy of its whole body. This enables the whale to make its deep dives and to remain at neutral buoyancy, while searching for prey. Sperm whales are known to dive to 3,300 ft (1,000 m) and may dive to more than twice this depth. They feed mainly on large, deepwater squid, as well as on some fish, lobsters and other marine creatures. Their sonar system is vital for finding prey in the black depths of the ocean.
All sperm whales migrate toward the poles in spring and back to the Equator in autumn, but females and young do not stray farther than temperate waters. Adult males, however, travel right to the ice caps in high latitudes. They return to the tropics in winter and contest with each other in order to gather harem groups consisting of 20 to 30 breeding females and young. Males under about 25 years old do not generally hold harems, but gather in bachelor groups.
Sperm whales have been hunted for their oil since the mid-18th century, and after serious population declines between the 1950s and 1980s, this species is now protected.
The gestation period for sperm whales is about 14 to 16 months. When a female gives birth, she is surrounded by attendant adult females, waiting to assist her and to help the newborn to take its first breath at the surface. As with most whales, usually only 1 young is produced at a time, but twins have been known. Mothers suckle their young for up to 2 years.
Distribution: Occurs throughout the world’s oceans, extending to the polar ice fields, occurring in areas of deep water. Populations tend to move towards the poles in summer.
Habitat: Deep oceans.
Weight: 12.7 - 36 tonnes (14 - 40 tons); males are at least a third bigger
Length: 11 - 16 m (36 - 52 ft); individuals up to 20.5 m (68 ft) existed until recently
Food: Mostly squid, including giant deep-sea squid, but also some fish and sharks.
Maturity: Females 7 - 13 years; males 25 years.
Gestation Period: About 18 months.
Breeding: 1 calf born every 5 - 7 years.
Life span: 77 years.
Pygmy Sperm Whale
Range: All oceans.
Habitat: Tropical, warm temperate seas.
Size: 10 - 11 ft (3 - 3.4 m).
Its underslung lower jaw gives the pygmy sperm whale an almost sharklike appearance, belied by its blunt, square head. The pygmy sperm whale’s head accounts for only about 15 per cent of its total length. There are 12 or more pairs of teeth in the lower jaw. Short, broad flippers are located far forward, near the head. The body tapers off markedly behind the small dorsal fin.
Pygmy sperm whales have often been sighted alone, but they are thought to form social units of 3 to 5 individuals.
Little is known of the reproductive habits of pygmy sperm whales. Gestation is believed to last about 9 months; calves are born in the spring and fed by the mother for about a year.
Dwarf Sperm Whale
Range: All oceans.
Habitat: Tropical and subtropical seas.
Size: 8 - 9 ft (2.4 - 2.7 m).
Superficially similar to the pygmy sperm whale, the dwarf sperm whale tends to have a more rounded head than its relative, though there is considerable individual variation in shape. The whale’s lower jaw is set back, and it contains up to 11 pairs of teeth.
Little is known of the biology and habits of this whale, but fish and squid are believed to be its main items of diet. Species found in the stomachs of dwarf sperm whales are all known to live at depths of more than 250 m (800 ft), so there seems little doubt that these whales make prolonged dives for food.