Sperm Whale – Physeter macrocephalus
The Sperm Whale, also known as Cachalot, belongs to the family of the Sperm Whales and is thus part of the infraorder of the whales (Cetaceans). Physeter macrocephalus was first described by Linnaeus in 1758. Sometimes one finds it also under the scientific name Physeter catodon.
The genus Physeter is monotypic, i.e. the Wperm whale is the only species of the genus. Moreover, it is the only big whale in the suborder of the toothed whales and also the largest toothed creature on earth.
Description, Anatomy & Characteristics
Name-giving is a substance found in the head of the Sperm Whale that was mistaken with the semen of the species.
The head can account for up to a third of the total length of the body.
Males become clearly bigger. They reach lengths of over 20m and a weight of over 50t. Females however become “only” 12m long, with a weight of 15t. There are indications that there were much larger animals before commercial whaling. A pair of teeth in the New Bedford Whaling Museum measuring 30cm indicate an animal well over 20m and 100t.
The colouring of Physeter macrocephalus is uniform grey.
Other striking features are the small lower jaw, the stub-like flippers, a small fin and several humps between fin and fluke.
Normally only the teeth of the lower jaw break through, while those in the upper jaw remain invisible.
Habitat, Distribution & Occurrence
The Sperm Whale occurs worldwide in all oceans. Males are observed as far as the polar seas and their marginal seas, while females and calves are more likely to be seen in tropical and subtropical latitudes. They avoid waters with superficial water temperatures below 15°C. The dark blue dots on the map show places with high incidences of Physeter macrocephalus.
The Sperm Whale is often found above deep waters. In addition, Physeter macrocephalus can be seen near the coasts, but prefers areas with a depth of about 1000m. They can often be observed on the continental shelf, where the seabed sinks rapidly.
It is known that adult males go to shallow bays to rest. There are also populations, e.g. in Scotland, that mainly live near the coast. Before commercial whaling there were probably several of these populations.
Although they are very rarely seen diving in the Canary Islands, whale watching tours are usually more successful.
Biology & Feeding
While older males live solitary, young bulls and mothers with calves can be found in associations. The groups of mothers with calves include about 15 to 20 animals. Before the time of the whaling, these should have been far bigger.
Although the Sperm Whale is not known to cooperate with other species, it has been observed more often that they have travelled with individual animals of other species. They were even treated almost like their own young. The reason for this behaviour has not yet been clarified.
The food of Physeter macrocephalus consists mainly of cephalopods, but also medium-sized fish and large crustaceans have been found in stomachs. Especially in bulls, which live in northern latitudes, fish seems to make up a larger part of the food.
Reproduction & Development
At the mating-time, the males join the females again. A male maintains a harem with approximately 10 females on that occasion. Furthermore there are observations, which allow different conclusions. On the one hand it is assumed that there is a fight between males for the harem control. On the other hand it can be that the fights determine only one hierarchy within the harem.
The gestation period is estimated at 10 to 17 months. A calf weighs about 1t at birth and is between 4 and 5.5m long. The breastfeeding period is one to two years. While the sexual maturity already occurs with females with 9 years, this happens with bulls only with 25 years.
Due to the growth rings of the teeth, a life expectancy of around 70 years is assumed.
The Sperm Whale and its predators
Except the human being, a full-grown sperm whale actually has no enemies. Only old, injured or young animals can be attacked by orcas or big sharks. In the event that a school of Sperm Whales is attacked, young and weakened animals are encircled by their conspecifics. These then stand with the flukes outside, in order to beat away approaching enemies with these. In addition, it was observed that bulls in distress, who are actually alone on their way, join a group to seek shelter.