Risso's dolphin  (Grampus griseus)

Classified as Least Concern (LC) on the IUCN Red List (1). Listed on Annex IV of the EC Habitats Directive, and Appendix II of the Bonn Convention (North and Baltic Sea populations), and Appendix III of the Bern Convention (3). All cetaceans (whales and dolphins) are listed on Annex A of EU Council Regulation 338/97; they are therefore treated by the EU as if they are included in CITES Appendix I, so that commercial trade is prohibited. In the UK all cetaceans are fully protected under the Wildlife and Countryside Act, 1981 and the Wildlife (Northern Ireland) Order, 1985 (4).

Risso's dolphin is a large, stocky species with a blunt head (2). They are easily recognised as they are heavily scared and become whiter with age as the number of scars increases (2). Calves are born with grey skin that turns chocolate brown as they age (5), eventually they take on the adult colouring of a grey back and white underside with darker flippers and tail (5). The scars are thought to be caused by the teeth of other Risso's dolphins, due to playing or fighting, however it is also thought that some of the scars are the result of squid bites (2). The tall, centrally positioned sickle-shaped dorsal fin is even taller and more erect in adult males than in females (6).

Widely distributed, inhabiting tropical and warm temperate waters of both hemispheres (7). In UK waters the main concentration is around the Hebrides, but the species also occurs around the Northern Isles and in the Irish Sea. It is also quite common in south-east and western Ireland (4).

Shows a preference for deep, warm temperate and tropical waters in offshore areas (7). Risso's dolphins are fairly abundant, with wide distribution. They prefer deep off shore waters, but can be seen close to shore around oceanic islands. In Britain and Ireland most records are within 11 kilometres of the coast (8).

Risso's dolphin feeds largely on squid, although other cephalopods are also taken, as well as fish and crustaceans (2). Like most dolphins, this species is a highly social animal, typically occurring in groups of between 3 to 50 individuals (2), and may mix with different species of cetaceans (whales and dolphins) (9). When groups are hunting they spread out into a long line (5). This species tends to ride alongside or in the wake of boats, and young individuals often breach (clear the water), slap their flippers on the surface of the water or 'spyhop' (lift their heads clear of the water) (5). A number of sounds are produced, including characteristic 'signature whistles' (7), many of these vocalisations are important in detecting prey through echolocation (9).

This dolphin is vulnerable to hunting (5) and environmental change, chemical and noise pollution (9), and entanglement in fishing nets, which results in drowning (5).

A UK Biodiversity Action Plan priority species, Risso's dolphin is protected in UK waters by the Wildlife and Countryside Act 1981 and the Wildlife (Northern Ireland) Orders, 1985; it is illegal to intentionally kill, injure, or harass any cetacean (whale or dolphin) species in UK waters (4). The Agreement on the Conservation of Small Cetaceans in the Baltic and North Seas (ASCOBANS) has been signed by seven European countries, including the UK. Provision is made under this agreement to set up protected areas, promote research and monitoring, pollution control and increase public awareness (4).

To learn more about the conservation of whales and dolphins see:

• Whale and Dolphin Conservation Society:
  www.wdcs.org

Information authenticated by WDCS, the Whale and Dolphin Conservation Society.
http://www.wdcs.org

• Crustaceans: diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, slaters, woodlice and barnacles.
• Echolocation: detecting objects by reflected sound. Used for orientation and detecting and locating prey by bats and cetacea (whales and dolphins).

1. IUCN Red List (November, 2008)
   http://www.iucnredlist.org
2. Cawardine, M., Hoyt, E., Fordyce, R.E. and Gill, P. (1998) Whales and Dolphins, the Ultimate Guide to Marine Mammals.Harper Collins Publishers, London.
3. Council of Europe: Bern Convention (June, 2002)
   http://www.coe.int/t/dg4/cultureheritage/conventions/bern/default_en.asp
4. UKBAP (June, 2002)
   http://www.ukbap.org.uk/
5. WDCS (June, 2002)
   http://www.wdcs.org
6. Macdonald, D.W. (2001) The New Encyclopedia of Mammals.Oxford University Press, Oxford.
7. Cetacea.org. (June, 2002)
   http://www.cetacea.org/rissos.htm
8. Carwardine, M. (1995) Whales, Dolphins and Porpoises.Dorling Kindersley, London.
9. Burnie, D. (2001) Animal.Dorling Kindersley, London.