The Risso’s dolphin (Grampus griseus) is the smallest member of the subfamily Globicephalinae (Delphinidae). It is characterized by robust build and rounded head.
. The colour of its skin and the scarification patterns changes though their lifetime. When calves are born, they are dark grey, and they turn whiter as they growth to adults due to scars in their skin. These scars are caused by the competition between individuals of the same species or with confronts with their main prey, cephalopods. Therefore, the individuals can then be identified by the scarification patterns of their dorsal fins.
This species is cosmopolitan and is widely distributed from tropical to warm oceanic waters. In the North Atlantic, they are known to be distributed from New Foundland to the Caribbean Sea, mostly occurring in the European coasts from Norway to Greece and around the Macaronesian Islands. They prefer habitats where the steep slopes are between 400 to 1,200 m depth or near submarine canyons and seamounts.
They form social group with a mean of 10 to 30 individuals, with a body length about 2.6 to 4 m long and adults may weigh between 300-500 kg. The calving season is between June and August, reaching the sexual maturity at 8-10 years for females and 10-12 years for males. The protective status of Risso’s dolphin is listed as data deficient.
The Azores is a breeding, foraging and nursing area for Risso’s dolphin, being a resident species of the waters of Azores. It was first seen, by a whale watching trips.company, in the archipelago in 1992. However, although they can be seen all year around in these waters, they are just sighted a few times. This can be because they are relatively shy cetaceans and do not readily approach boats. Other hypotheses is because their diet is mainly composed of deep-water cephalopods, which leads to a distribution in deep, not being able to see them at surface many times.
Article written by Margarida Leal.
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