The Sperm Whale
(Physeter macrocephalus)

Sperm whales have huge heads - about 40 percent of their entire body length - and possess the largest brain of any creature that has ever lived on Earth.

The sperm whale got its name from an organ inside its head - the spermaceti organ - which whalers used to believe produced sperm. In fact the organ contains high quality oil. Sperm whales were hunted commercially in the 18th and 19th centuries for spermaceti oil blubber and meat. The famous literary classic, Moby Dick tells the story of a 19th century sperm whale hunt. The whales are very difficult to study because they spend most of their time in deep water, usually away from coastlines.

Male sperm whales grow to around 18.3m and females to about 13.1m long. Male and female sperm whales have huge, squarish foreheads, and a long, narrow lower jaw. Sperm whales have one blowhole on the left of the forehead. Their "blows" are projected forward at a different angle from other whales, giving them a distinctive shape. Their light-brown to blue-grey skin is rippled, especially on the back and sides.

Researchers believe that sperm whales may not have good vision as they have disproportionately small eyes. However, in the dim ocean environment, vision is often not the most important sense. In fact, blind sperm whales have been captured in perfect health with food in their stomachs. Rather than relying on eyesight, sperm whales are believed to use echolocation to find prey and to navigate.

Where are they found?

Sperm whales are found in all oceans, and are divided into northern and southern hemisphere populations. They do not migrate between warmer and colder seas like other baleen whales, although there are regular seasonal shifts in sperm whale populations. Like other large whales, sperm whales move North in the summer to feed. Males can be found in subarctic waters, while females and juveniles are less likely to migrate as far north. Only the large mature male sperm whales are found in the polar seas, the Davis and Denmark Straits, off western and northern Norway, and occasionally near Svalbard and in the Barents Sea.

What do they eat?

Giant squid comprise about 80 percent of the sperm whale diet, and are swallowed whole. The remaining 20 percent comprises octopus, fish, shrimp, crab and even small bottom-living sharks. A large, male sperm whale will eat about 1.1 tonnes of food a day, although a female only requires a quarter of this amount. Sperm whales can dive to 915m in pursuit of giant squid, their primary prey. They are among the deepest marine mammal divers, and dives can last more than an hour. Males have been known to dive 1200m while females dive to at least 1000m.

How long do they live?

Females can conceive when they are about 8.5m long, while male sperm whales are probably not able to mate until they are 11.9m long. After a 14 to 16 month gestation period, 3.7 to four metre calves are born. Sperm whale herds appear to be organized on a harem system similar to elephants, where a solitary bull sperm whale joins a school of 10 to 40 adult females, their calves, and juveniles of both sexes for the breeding season.

Sperm whales die of natural causes, and have been known to mass strand. The teeth of the sperm whale can be used to find the age of the animal. They are composed of dentine, which is deposited in a series of annual layers. Age can be determined by sawing the teeth in half and etching them with acid to help distinguish between the different layers. The layer counts show that sperm whales live for more than 60 years.

Sperm whales and hunting

The impact of commercial hunting in the past, as well as recent environmental change, has resulted in decreased sperm whale stocks, and in many areas sperm whales are considered endangered species. Hunting has been banned by the International Whaling Commission since 1981.

Conservation concerns

Sperm whale populations are even more difficult to estimate than those of other whales, mostly due to their capacity to remain submerged for long periods. They are susceptible to threats from environmental change, human actions and disturbance.