A large, robust Dolphin, this species reaches up to 3.8metres in length and has a large quite upright dorsal fin. The colour varies greatly with age and between individuals. At birth they are pale grey which then changes to a dark grey/brown colour. Later in life the colours lightens again to an almost silvery grey and they often have lots of scars and scratches across their body. These are thought to be caused by other Risso's Dolphins and Squid, a main food source for the species. A very identifiable feature of this species is the blunt head that lacks the distinctive beak of many of the other Dolphin species.
Risso's Dolphins inhabit all of the major oceans and live in most areas except for the polar regions; the North of Scotland is their northern limit. They tend to be found in deeper water as this is where the majority of their prey is found, however occasionally they can come into more coastal waters as they do around Mull. The number of sightings around Mull seems to have decreased within recent years, however it appears that this species may have been observed more in other areas around the Hebrides.
Around the Hebrides, Risso's Dolphins are usually seen in small groups of up to 20 individuals. Whilst they rarely approach boats and it is almost unheard of to see them bow-riding, they are very active as a species. You will often see them tail slapping, breaching and spy hopping and there is also a lot of interaction between individuals; this may account for a lot of the scarring that appears on some animals.
Risso's Dolphin's main prey is squid, however they will also feed on octopus and cuttlefish. They can dive for up to 30 minutes and reach depths of up to 1000 metres, however it has been suggested that they tend to wait until the prey moves up the water column at night and will feed then. They will feed co-operatively and will grasp prey in their lower jaw, but swallow it whole. As with many other species that feed on squid, Risso's Dolphins are susceptible to harm from accidentally ingesting plastic bags, assuming that they are food.