Risso's Dolphin
Risso's Dolphin inhabits deep tropical and warm temperate waters in both the Northern and Southern Hemispheres. They are not thought to migrate over large areas.
Classification: Risso's Dolphin was classified as Grampus griseus, meaning 'Grandfish' and 'grey' respectively.
Local Names: Grampus; Grey Grampus; White-Head Grampus; Grey Dolphin. Confusingly, several members of the 'Blackfish' family, in particular the immense Orca (Killer Whale) were called 'Grampus' in older literature and are sometimes still referred to as such.
Description:
This is a more 'barrel-shaped' dolphin with a large blunt head and no beak. In
this respect it is similar to the large Sperm Whale. Risso's Dolphins vary in
colour from blue-grey, grey-brown or almost-white, depending on age and
injuries. Scars from other male Risso's Dolphins can often be seen, dark on
lighter individuals and light on darker individuals. The mouth slants upwards
and there are seven or fewer pairs of teeth at the front of the lower jaw. The
dorsal fin is tall and curved, with a distinct point at the tip, rather like the
flippers. The tail stock is thick and ends in powerful flukes. Risso's Dolphins
measure between 2.8-3.85m in length, and they can weigh as much as 500kg.
Recognition at sea: The adult Risso's Dolphin is quite easy to recognise at sea with their distinctive scarring.
Habitat: Risso's Dolphins prefer warm temperate and tropical offshore waters and are only seen close to shore when the continental shelf is narrow.
Food & Feeding: The main prey is squid and octopi but they are also known to take fish.
Behavior: Risso's Dolphins are usually seen in groups of 3-50 animals. Occasional aggregations of up to 4,000 are also seen, and they often mix with other dolphin species. They often surface leisurely side-by-side in a form of 'chorus line' but when moving quickly are aerial acrobats and often breach, bowride and 'porpoise'. Risso's Dolphins create a series of varying sounds including signiture whistles. Mass and individual strandings are not uncommon.
