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The Risso's dolphin
Grampus griseus
​General description
With its robust and cylindrical body, the Risso's dolphin stands out for its unique appearance. Its prominent melon gives it a rounded head with no visible beak. Its dorsal fin, large and arched, is located in the middle of its back. It is also distinguished by its pectoral fins, thin and long, and its wide-spanning caudal fin. Risso's dolphins have a bluish-gray hue that lightens with age, their bodies becoming covered in white scars due to interactions with conspecifics or prey.
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Habitat
Cosmopolitan, the Risso's dolphin prefers tropical, subtropical and warm temperate waters. Mainly pelagic, it frequents deep areas, particularly when searching for food. It is particularly found in regions where the seabed slopes quickly.
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Diet
Teutophagous, the Risso's dolphin feeds primarily on squid, although it also takes fish on occasion. It is capable of diving to depths of more than 500 meters, with apneas that can last up to 30 minutes, although its typical dives are shorter and shallower (usually between 100 and 200 meters deep).
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Behavior
Risso's dolphins are social cetaceans. They live in groups of 10 to 30 individuals, but it is not uncommon to see them alone or in larger gatherings, sometimes numbering hundreds of members. They associate with other species of cetaceans, such as bottlenose dolphins. Very playful, they often jump out of the water, strike the surface with their fins or tail, and perform "spy-hops" (vertical body exit) to observe their environment.
Family : Delphinidae​​
Height (m)​​
Weight (Kg)
Lifespan (years)
Sexual Maturity
(years)
Gestation
(month)
2.75 – 4.00
300 – 500
40 – 50
10 - 12
2.75 – 4.00
300 – 500
40 – 50
8 - 12
12 - 16
Global distribution of the Risso dolphin, adapted from Hartman, Karin L. 2018. "Risso's Dolphin: Grampus griseus". In Encyclopedia of Marine Mammals (Third Edition), edited by Bernd Würsig, J.G.M. Thewissen, and Kit M. Kovacs, 824‑27. Academic Press. https://doi.org/10.1016/B978-0-12-804327-1.00219-3.
Observations in the Lesser Antilles (CCS)
Main threats
Risso's dolphins face numerous threats that compromise their survival. Entanglement in commercial fishing gear, such as gillnets and trawls, is a major hazard, leading to injury or death. Direct hunting for their meat and oil is also practiced. Furthermore, underwater noise from human activities disrupts their natural behavior and keeps them away from their essential habitats, even increasing the risk of stranding. Finally, environmental contaminants, such as heavy metals and organochlorines, accumulate in their bodies due to their position at the top of the food chain. These substances, coming from various sources such as industrial and urban discharges, threaten their immune and reproductive systems, particularly affecting coastal populations.
Least concern
IUCN Status :
References
- Sylvestre, Jean-Pierre. 2014. Cetaceans of the World Systematics, Ethology, Biology, Ecology, Status. Practical Guide. Quae Publishing.
- Rone BK, Sweeney DA, Falcone EA, Watwood SL and Schorr GS (2022) Movements and diving behavior of Risso’s dolphins in the Southern California Bight. Front. Mar. Sci. 9:873548. doi: 10.3389/fmars.2022.873548
- Patricia Arranz, Kelly J. Benoit-Bird, Brandon L. Southall, John Calambokidis, Ari S. Friedlaender, Peter L. Tyack; Risso's dolphins plan foraging dives. J Exp Biol 15 February 2018; 221 (4): jeb165209. doi: https://doi.org/10.1242/jeb.165209
- NOAA Fisheries
- International Whaling Commission