Risso’s Dolphin – Grampus griseus
Risso’s Dolphin, also known as the White-Headed Grampus, belongs to the family of the Dolphins (Delphinidae) and is thus part of the infraorder of the Whales (Cetacea). Grampus griseus was first described in 1812 by Georges Cuvier.
It is thought to be part of the kinship of the Pilot Whales, who are also part of the Dolphins. The genus Grampus is a monotypical taxon, which means, it contains only this one species.
In contrast to the general picture, which is made of a dolphin, Risso’s Dolphin has no long, drawn-out snout. On the contrary, its head profile is very steep, the head quite voluminous and the muzzle much wider than long.
In addition, the dorsal fin is comparatively large, the flipper are long and narrow and thefluke has a clear notch in the middle.
The colouration of Grampus griseus changes in the course of his life. Young calves are initially silver to grey, then become darker and as old juveniles almost black with few bright spots on the belly side. Then the colours fade into a slate grey. The colours of some parts of the body remain stronger than others. In addition, Risso’s Dolphin often have numerous scars scattered on their bodies. These result from both fights with conspecific, as well as from fighting with other species, such as sharks or cephalopods. Incidentally, these scars are more common in males than in females.
Grampus griseus can grow up to 4m long and weigh 650kg. As it is the case with many dolphins, males are somewhat larger than females.
Its dentition consists of two to seven pairs of teeth in the lower jaw, while in the upper jaw only stunted remains of teeth are present.
Habitat & Distribution
Risso’s Dolphin prefers to live in deep waters near the coast. It is therefore located on the continental shelf, where the water is about 400 to 1000 m deep.
In Europe you can observe Grampus griseus from the North Sea, along the European coast, across the British Isles, the Azores, Madeira and the Mediterranean Sea. The Canary Islands, like Hawaii, are a more far-out distribution area.
Its distribution area on the American Pacific coast extends from the Gulf of Alaska to the southernmost tip of the continent. On the Atlantic coast, it can be found from Tierra del Fuego to Rio de Janeiro and from Venezuela to the south coast of Greenland.
In the Indian Ocean, it is common to all shores except the east of Australia. It is also found throughout the Indo-Pacific region from Japan to the Philippines, Malaysia, Indonesia, Papua New Guinea and Australia. In the Red Sea Risso’s Dolphin is also distributed.
When diving in the Canaries, it is almost impossible to meet Risso’s Dolphin, due to his predilection for deep waters. On Whale Watching trips it is also quiet rare, as it usually stays away from boats. The best chances are probably the winter months, because Grampus griseus likes water temperatures of 15 to 20 ° C.
Risso’s Dolphin is a social animal that normally travels in schools of 10 to 50 animals, but also groups of up to 400 animals. In addition, they are sometimes seen together with other whales.
For communication they use different sounds, whereby whistles predominate.
The diet of Grampus griseus consists mainly of cephalopods. Only rarely do they chase crustaceans and fish. The composition of the food depends on the distribution area and seems to cover all kinds of cephalopods. So it eats octopuses, squids and cuttle fishes. The detection of the prey takes place by echolocation.