Risso's Dolphin

Risso's Dolphin: Grampus griseus

IUCN Status: Data deficient

Status and distribution summary:

Occurs in all temperate to tropical seas of the world, concentrated along the shelf edges and inshore near headlands. Not known to be migratory. Locally common in some areas, for example the west coast of Ireland.

Exploitaiton:

May be taken by local inshore hunts but not thought significant

Where is it usually seen:

Is recorded anywhere from the outer Channel and Bay of Biscay, though probably more frequent close to coasts.

Frequency of sightings:

Not infrequent, but sporadic, suggesting nomadic behaviour. Usually occurs in small to medium sized groups (3-20). Seen more often in summer, though this could be a function of calmer seas making viewing easier.

Recognition:

Large dolphin, reaching 3.5 metres in length.

Upper parts are all grey; relatively dark in juveniles, but increasingly pale with age.

Adults are usually covered in whitish scars, inflicted during dominance contests by other Risso's Dolphins.

Very tall, thin dorsal fin, which is slightly falcate and is more upright than in other dolphins, and is round tipped.

Blunt headed, with a steep forehead and virtually no beak.

Behaviour:

Usually seen in small pods (usually 3 - 20 in our waters but can occur in very large schools of over 100).

Often swims slowly at the surface, milling lazily. Breathes regularly, every 15 seconds or so when at the surface. Dives for variable periods, up to 30 minutes.

When active, will half-breach frequently, lob-tail or spy-hop.

In steady swimming, domed forehead breaks the surface when breathing, often before dorsal fin is seen.

Confusion species:

  • Bottlenose Dolphin; is similar in size and overall colouration, but have shorter and more falcate dorsal fin, lacks extensive scarring, and has a distinct beak which is often visible at the surface.
  • Female and juvenile Killer Whales; have similar dorsal fins, but are black with white head patches and no scarring.
  • Grey Cuvier's Beaked Whales; are possibly confusable, with similar paling of upper parts, however, the dorsal fin is set well back, and is small and falcate.