Rough-Toothed Dolphin – Steno bredanensis
The Rough-Toothed Dolphin belongs to the family of dolphins (Delphinidae) and is therefore part of the infraorder of whales (Cetaceans). Steno bredanensis was first described in 1823 by Georges Cuvier.
Steno is a monotypic taxon, which means that there is only this one species in the genus.
Description, Anatomy & Characteristics
The main characteristic of the Rough-Toothed Dolphin is its conical head with a narrow snout.
The back is dark grey, the flanks light grey and the belly white to light pink. Steno bredanensis can also have white spots on the sides and dark spots on the back. Sometimes a white line runs between the dark grey of the back and the light grey of the flanks.
As their colloquial name suggests, they have teeth with a roughened surface caused by numerous irregular grooves. Both the upper and lower jaws have between 19 and 28 teeth on both sides.
Steno bredanensis grows up to 2.83m long, weighing up to 160kg. Males are usually somewhat bigger than females on that occasion.
Habitat, Distribution & Occurrence
The Rough-Toothed Dolphin is found in the tropical, subtropical and temperate latitudes of all oceans. It is also found in the Mediterranean Sea, Red Sea and the Caribbean. It must be said that almost all sightings are made on the high seas, where the water is at least 1000m deep. Steno bredanensis is therefore very rarely observed near the coasts.
While scuba diving on the Canary Islands it is almost impossible to observe the Rough-Toothed Dolphin. But with a little luck you can see it at whale watching trips. Then probably rather in the summer months, as it prefers water temperatures around 25°C.
Biology & Feeding
Although there are sightings of individual animals, Steno bredanensis usually occurs in social associations of 10 to 100 animals. They swim either in a loose group, with different speed or in a closed compound, in which they coordinate direction and speed exactly one on the other. In addition, individual animals listen to the sonar sounds of other group members instead of constantly producing ultrasonic calls themselves.
Among the Rough-Toothed Dolphin, surfers are observed much less frequently than in other species. However, they often swim with head and neck above the water.
It has also been observed that they travel together with other whale species.
Reproduction & Development
Little is known about the reproduction of the Rough-Toothed Dolphin. Females give birth to a calf that is between 100 and 130 cm long at birth. The calves suckle, rest and play daily. The playing time follows the suckling. At noon the young animal rests for about an hour. After 2 months the young begins to eat fish and is less suckled. How long the intensive relationship between mother and calf lasts is unknown. It was observed how a female kept a dead calf on the surface for several days! It was protected from possible attackers by male conspecifics.
Within the first five years the animals grow the most. While females reach sexual maturity at the age of 9 to 10, males do so between 5 and 10 years.
Rough-Toothed Dolphins off the coast of Japan reach an age between 32 and 36 years. However, it is assumed that Steno bredanensis can get much older. The oldest animal is estimated to be 48 years old.