Sperm Whales

Sperm whales are the largest of the toothed whales (Odontoceti) with a size of 16m for adult males and 11m for adult females. This sexual dimorphism, which means the differences in body shape, length, weight and colouration between male and female of one species, is the biggest within the group cetacea (whales, dolphins, porpoises). Males weigh 45-50t, females 15-20t.

They have the biggest brain of all animals but relative to body size it is not bigger than those of other whales and dolphins. The skull of the sperm whale is extremely asymmetric resulting in a blow which is directed forward and to the left.

Teeth are only in the lower jaw but one tooth can be up to 20cm long and can weigh as much as 1kg. The teeth in the upper jaw usually do not erupt.

If you look at a the head you will find it box-shaped. The reason for that is the spermaceti organ which is placed above the upper jaw. It consists of a spongy tissue filled with spermaceti oil. The spermaceti oil is like a wax and is one reason for the hunting of sperm whales in earlier days because this wax burns soot free.

The function of the spermaceti organ is the transmission of sounds. Between upper jaw and spermaceti organ is another very interesting structure which is called junk.

The junk contains acoustic lenses which focus sound before it leaves the head like an optical lens focus light. With these lenses sperm whales can produce sounds which are focused on a tiny area like the beam of a search light or a torch. In a distance of 1m to the animal the volume of the sperm whale's sound can reach 223 db which is a bit less than the explosion of 0.5kg gunpowder. But because of the acoustic lenses the sound is very loud even in bigger distances.

Have you heard about the big bang theory? The big bang theory is about sounds produced by these whales which are loud enough to paralyse or even to kill a squid.

The spermaceti organ of male these whales grows through their whole life and is not only a sound transmitter but also an attraction to females. The bigger the better. That should be enough about the their head although it makes up one fourth to one third of the total body length.

Sperm whales have small paddle shaped flippers and a nearly triangular fluke. The dorsal fin is small and rounded and may be topped by a white callus in females.

Females usually give birth to one calve after a gestation period of 14-16 months. The calve is 3.5 to 4.5m long and weighs about 1t. Since most female sperm whales give birth only every five years and get sexually mature with an age of nine years you probably can imagine why it lasts so long until over hunted populations have recovered.

Calving occurs in tropical or subtropical waters where the females spend most of their life time. Females prefer a water depth of more than 1000m and mostly stay far away from land. In these waters they live in groups with other female whales and their young. These groups are called family units.

These family units travel about 35000km per year. The calves are not able to dive as deep as their mothers. So they stay at the surface while the mother is hunting food. However a lonely calf would be an easy prey for e.g. killer whales or big sharks. Probably this is the reason why the adult whales of one family unit dive asynchronous. So there are always some females at the surface which take care of the calves. There were also females observed suckling calves which were not their offspring which is rarely the case in the animal kingdom.

So Sperm whales are obviously highly social animals. The Males stay within the family unit until they are 4 to 21 years old. Afterwards they build loose aggregations. The older the males are the further south they occur. Old males usually live solitary close to the ice edge and swim to the tropical and subtropical waters for mating only.

When these whales start a foraging dive they raise their fluke above the sea surface and then go down vertically to a depth of about 400m where they usually stay for 30 minutes.

There they hunt their prey which mainly consists of squid but depending on the geographic region fish can make up the bigger proportion, too. That is what these whales mostly do but they can dive as deep as 3000m and for more than one hour.So these whales are outstanding in many ways.

If you like to learn more about these whales, we recommend the following book:Whitehead, H. (2003): Sperm Whales – Social Evolution in the Ocean. The University of Chicago Press.