Illustration: Les Gallagher ©ImagDOP

Risso's Dolphin

Grampus griseus

The Risso's Dolphin is a quite distinctive species. The head ends at an abrupt angle and there the beak is not present. In the forehead a V-shaped groove that can clearly be seen when the head is clear off water. The colour is a dark grey when the animals are young, but rapidly the skin surface presents discoloration and a great amount of scars, that can eventually render the body almost completely white.

It's a gregarious species that can form groups between 20 and some hundreds of individuals and that can sometimes be seen associated with other cetacean species, specially Pilot-whales. The scars covering the bodies of the older animals must be mainly due to social disputes, and are left by the small teeth that in the species are no more than seven pairs in the lower jaw.

They feed mostly in cephalopods (squids and octopuses), but may occasionally include other prey items as fish. Sometimes the animals are seen travelling in a chorus-line, which may constitute a hunting strategy.

The studies on this species are very scarce and thus the reprodutory biology is poorly understood.

In the Azores the Risso's Dolphin are relatively common and can be seen with frequency near the shore, during most of the year. It's probable that there are resident groups and its common to see groups with calves during the Summer. They are shy and seem to be highly disturbable by the presence of boats, but sometimes they can show a great curiosity, approaching the boats and performing spectacular aerial behaviours.

Text: Rui Prieto