Risso's Dolphin
Grampus griseus

Other Names: Gray Dolphin, White-head Grampus, Gray Grampus, Grampus

Habitat: Offshore and inshore

Status: Common

Population: Unknown

Threats: Hunting/whaling and entanglement in fishing nets

Group Size: 3-50, temporary gatherings of several hundred

Fin Position: Center

Newborns: 4 ¼-5 ¾ ft (1.3-1.7 m), Unknown weight

Adults: 8 ½-12 ½ ft (2.6-3.8 m), 660-1,100 lb. (300-500 kg)

Diet: Squid or octopus and occasionally fish

Teeth: 0 on top row, 4-14 on bottom row

Description

Dorsal fin:

- very tall dorsal fin, up to 20 in (50 cm) high
- tip may be rounded or pointed
- concave trailing edge

Flukes:

- pointed tips
- distinct notch in middle
- flukes have "swept-back" appearance
- broad, dark flukes

Flippers:

- long, sickle-shaped flippers
- pointed tips

Jaw Bone:

- strong, oval teeth at tip of lower jaw

Other characteristics:

- slightly bulging forehead slopes steeply to mouth
- mouth line slopes upward
- body covered in white scars
- blue-gray, gray-brown, or almost white body color
- narrow tail stock
- pale underside (variable)
- body robust in front of fin

Behavior

- young animals are known to breach; older animals tend to do a half-breach, then slap side of head onto the surface
- it occasionally spyhops high in the water, with flippers exposed
- may lobtail and flipper-slap, and will surf in waves
- seldom bow-rides but may swim alongside a vessel or in its wake
- typically dives for 1 to 2 minutes, then takes up to a dozen breaths at 15- to 20-second intervals; can stay underwater for up to 30 minutes
- flukes may appear above water when diving
- sometimes swims by porpoising
- may surface at a 45° angle to breathe
- groups sometimes spread out in a long line when hunting
- some groups very shy, but others allow a close approach

Distribution

- deep tropical and warm temperate waters in northern and southern hemispheres
- fairly abundant, with a wide distribution
- prefers deep offshore waters, but may be seen close to shore around oceanic islands and where there is a narrow continental shelf
- in Britain and Ireland, most records are within 7 miles (11 km) of the coast
- in USA, found primarily near the shelf edge
- present year-round in most of range, although there may be a seasonal onshore-offshore movement in some areas
- sometimes found in cooler regions during summer months

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