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Risso’s dolphin

a scientific drawing of a risso's dolphin

Scientific Name: Grampus griseus (Cuvier, 1812).

Common Name: Risso’s dolphin.

Classification: Odontoceti, family Delphinidae.

Physical notes: Up to 4 m and 500 kg. Heavily scarred body with a blunt, rounded forehead and no beak. Uniform dark grey to patchy grey-and-white as they get older.

Distribution and habitat use: Tropical to temperate waters in both hemispheres. Inhabits coastal and oceanic waters between 200 and 1000m, with a preference for waters above 12ºC and areas with a steeper upper continental slope.

Group size: Normally seen in groups of 5 to 30 individuals, but occasionally larger groups of 100 can be encountered.  Stratified group structure with stable clusters grouped by age and sex classes..

Life span: At least 30 years.

Gestation period: 13-14 months. Calves are born with ca. 1.35m. Females reach maturity at 8-10 years and males at 10-12 years.

Diet and Feeding: Mainly deepwater squid and octopuses and other cephalopods. They can dive up to 500 m and hold their breath up to 30 minutes.

Typical Behaviour: During the daytime it is usually socializing (performing breaches, spyhops, headslaps, lobtails) resting or travelling. Typically, doesn’t approach boats, maintains a ‘personal space’ and slowly turns away.

Population: Unknown, it is estimated that the sum of existing is 350 thousand, but it is likely to be a fraction of the actual total. The population trend is unknown.

Threats: By-catch in fishing activities, pollution of heavy metals and plastic, noise exposure.

IUCN status: Least concern for overall species worldwide (2018). In Portugal, vulnerable (2023), and Mediterranean sub-population Data Deficient (2010).

Carwardine, M. (2022). Whales, Dolphins and Porpoises. Bloomsbury Wildlife. London, United kingdom.

Ferreira, M., Eira, C., López, A., & Sequeira, M. (2023). Grampus griseus golfinho de Risso. In Mathias, M. L. (coord.), Fonseca, C., Rodrigues, L., Grilo, C., Lopes-Fernandes, M., Palmeirim, J. M., Santos-Reis, M., Alves, P. C., Cabral, J. A., Ferreira, M., Mira, A., Eira, C., Negrões, N., Paupério, J., Pita, R., Rainho, A., Rosalino, L. M., Tapisso, J. T., & Vingada, J. (eds.): Livro Vermelho dos Mamíferos de Portugal Continental. Fciências.ID, ICNF, Lisboa.

Shirihai, H.  (2006).  Whales, Dolphins and Seals: A Field Guide to the Marine Mammals of the World.  Bloomsbury Wildlife. London, United Kingdom.

Still, R., Harrop, H., Stenton, T., & Dias, L. (2019). Europe’s Sea Mammals Including the Azores, Madeira, the Canary Islands and Cape Verde: A field guide to the whales, dolphins, porpoises and seals. Princeton University Press.