Risso's dolphin

Latin: Grampus griseus

Manx: Lheimmeyder marrey garroo

IUCN Red List status: Least Concern

Physical description

The Risso’s dolphin is a large, robust dolphin with an adult body length of 4 metres (13ft). The head is square and beak-less. The dorsal fin is large in comparison to body size and can be sickle shaped or tall and straight. Body colour can range from dark grey to almost white, depending on the level of scarring on an individual.

Heavy scarring is almost always apparent in adult Risso’s dolphins and is caused by two main factors; feeding and fighting.  Scarring can be inflicted by the tentacles and beaks of their chosen prey; squid, cuttlefish and octopus (cephalopods), but can also be caused by the teeth of other Risso’s dolphins. The amount of scarring on an individual can help us estimate age as scars can build to such extent that some mature Risso’s dolphins are almost completely white.  

Manx distribution

Risso’s dolphins return to the Isle of Man every year in March or April and stay until September.

They can be observed close inshore at hotspots such as Port St Mary, Marine Drive and Langness and on the west at Niarbyl. These coastal areas have water depths of just 22-35 metres, which is quite different to their worldwide habitat.

During the summer months, Risso’s dolphins are often seen around the Calf of Man, either passing through The Sound, or between the Calf and Chicken Rock. Nursery pods involving a number of mothers and calves are usually seen every year. 

Group size in Manx waters is 8-20 individuals, on occasion groups may come together but it is extremely rare to see any more than 40 Risso’s dolphins in one place. 

Risso’s dolphins can be mistaken for Orca due to similarities in appearance, see here for more information. 

Worldwide distribution

Relatively little is known about the Risso’s dolphin and no worldwide population estimates exist. They have been observed in temperate and sub-tropical waters as far north as Greenland and as far south as New Zealand and are found throughout the Mediterranean.  They usually favour steep shelf edge habitats 400-1000 metres in depth where they prey on bottom dwelling cephalopods.

There are only a handful of inshore populations in Europe, of which the Isle of Man is one.  In Britain, they are spotted around the Western Isles, Hebrides, Wales and Cornwall. 

Photo by Jon Penman

Risso’s dolphins have a relaxed travelling pace, but they do break out into bursts of highly active behaviour during or after foraging. This behaviour can include breaching, head slapping, spy hopping, head and tail standing, swimming upside down and logging. Such behaviours are generally only observed in the ‘square headed’ cetaceans, with other examples being pilot whales and killer whales.


Risso’s dolphins are deep divers and prey on cephalopods (squid, cuttlefish and octopus.)

Keep on Gramping participants
Risso’s research worldwide

Within the marine mammal science community, there are few who focus on the study of Risso’s dolphins. In fact, the Isle of Man is one of only 16 Risso’s study sites in the world. 

In 2019, MWDW joined 25 other Risso’s researchers at the World Marine Mammal Conference in Barcelona. One of the outcomes of the workshop was to produce a website and Facebook page which compiles all known Risso’s dolphin research papers and information in one place. Bryony from MWDW helped lead this project and created the Keep on Gramping website. 

Report a Sighting

Have you seen a Risso’s dolphin in Manx waters? Report your sighting to us.