How big is a Risso's dolphin?

Risso's clock in at up to 4m in length and up to 500kg in weight. The species is the biggest of the cetaceans we call 'dolphins'. They have blunt heads with an indistinct beak and a V-shaped cleft at the front, and a tall dorsal fin. There is a huge variation in colour, according to, among other things, age and region.


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Where are Risso's dolphins found?

Worldwide, from tropical to cool temperate waters, but they prefer the deep waters beyond the edge of continental shelves. They can be seen off the UK - the majority of UK sightings are off the west coast of Scotland and the Outer Hebrides.

Why are Risso's dolphins scarred?

Risso's is the most heavily scarred of all dolphins. They are born grey and gradually accumulate pale scarring as they age, to the extent that they can appear almost white. These scratches are known as 'rake marks' and are inflicted by members of their own species when playing or fighting, using the teeth. The scarring patterns are unique and can help scientists to identify individuals.

Who is Risso's dolphin named after?

The species is named after French naturalist Antoine Risso (1777-1845), who is also immortalised in the names of Risso's lanternfish and many species of marine snail

What do Risso's dolphins eat?

Risso's dolphins mostly prey on squid and octopus, but are also known to take cuttlefish and krill. They tend to 'suck in' their food, rather than chomping it down using their teeth, which explains why they have relatively few - just 2 to 7 pairs in their lower jaw, and only vestigial teeth in the upper jaw. In comparison, a bottlenose dolphin, which uses its teeth to capture prey, has more than 80 teeth across both jaws. Risso's use their teeth more for social interactions.

How do Risso's dolphins breed?

Gestation is around 13-14 months. Females form 'nursery pods' and take it in turn to forage while others look after the young. It's still not known when weaning takes place.

What Risso's dolphin research is taking place?

Risso's dolphins are not as well known as other dolphin species, and there is still a lot we don't know about them. Studies are currently being carried out off the Balearic Islands by the Altinak Research Institute. The species was recently declared Endangered by the IUCN in these waters.


Main image © Enrique Aguirre Aves/Getty


Sarah McPhersonFeatures editor, BBC Wildlife Magazine