Risso’s Dolphin (Grampus griseus)
Suborder: Odonticeti Family: Delphinidae
Occurs in Hawaiian waters.
Other known names:
Grey dolphin, White-head grampus, Grey grampus, Grampus
General description and habits:
Risso's dolphins are quite easy to identify, especially when they get older because they become scarred and battered. They only have teeth in the front of their lower jaw. When born they are gray all over, and then become chocolate-brown and eventually pale gray with a pale underside. Their flippers and tail remain darker, and the flukes are broad with pointed tips. They have a very tall dorsal fin that can be up to 20 inches high, the tip of which may be curved or pointed. Instead of a beak, it has a blunt head with bulging forehead that slopes steeply to the mouth that curves upwards. Adults weigh 300 - 500kg. Risso's do not often 'bow- ride' in front of boats, but may swim beside or in the wake of the boat. They generally swim in groups of between 3 and 50 animals. These groups spread out in a long line when hunting for food. Some groups are shy, but some allow humans to approach close to them. Young animals are energetic, and may breach, slap their flippers against the surface of the sea, spyhop, or surf in the waves.
Identity Keys to use in the field:
Robust body, abrupt forehead, single blowhole, gray in color, lighter under-side, tall dorsal fin, white scratches and scars. Adults range from about 2.6 to 3.8m (8.5 to 12.5ft), and newborns from 1.3 to 1.7m (4.25 to 5.75ft).
Squid and fish
Risso's dolphins have a wide distribution. They prefer deep offshore waters. They keep within warm waters, but sometimes have been spotted in cooler regions during the summer.
Common in certain areas but population size is unknown.
Hunting, entanglement in fishing nets, environmental changes
Hybrid offspring from Risso’s (x) Bottlenose matings have been seen both in captivity and in the wild.