Science for our seas
Taxonomy
Scientific name: Grampus girseus.
Order: Artiodactyla.
Family: Delphinidae.
Genus: Grampus.
Risso's Dolphin
IUCN Status
Least concern.
Other names
Grampus.
Grey grampus.
White-headed grampus.
Gee gee’s.
Appearance
A large dolphin that can grow up to 4 meters in length. Adults are grey and normally covered in whitish scars from fighting, whereas the juveniles are relative dark but get paler as they get older. The dorsal fin is tall and thin, and is sickle shaped with a rounded tip and is more up right than other dolphins. Their head is blunt, but they lack a beak.
Habitat and distribution
Currently, there is no estimate for the overall population of Risso’s dolphins. They are found in temperate to tropical waters and are normally seen off continental shelves.
They head is blunt and the forehead is steep, and they lack a beak.
Behaviour
Risso’s dolphins are normally seen in small pods between 3 to 20 dolphins but have been observed in pods of over 100. They are often swimming slowly at the surface, but are very active; they’ve been seen breaching, spy-hopping and head-slapping. Risso’s dolphins have been seen interacting with other species such as bottlenose dolphins. When they are steadily swimming, their foreheads break the surface, often before the dorsal fin is seen.
Confusion with other species
Bottlenose dolphins: they are similar in size and coloration but have a shorter more sickle-shaped dorsal fin, and they have a distinct beak.
Female and juvenile killer whales: they have a similar dorsal fin but are black with white heads patched and no scaring.
Threats
Risso’s dolphins are threatened from entanglement in fishing gear, pollution from toxic chemicals, collisions with boats, and entanglement in fishing gear.
Interesting facts
Risso’s dolphins can dive to depths of about 1,000 meters.