- Scientific name: Grampus griseus
- Also know as: Grampus Dolphin, Grey Dolphin
- Size: Up to 12 feet in length and 1000lb in weight
- IUCN Status: LC (Least Concern)
- Distribution: Found in relatively deep waters in all of the seas and oceans of the world.
- Feeds on: Mostly thought to feed on squid but will also eat fish.
- Description: Large, robustly bodied dolphin species. The body is stout and tapers to a relatively small tail. Head is large and bulbous with a large mouth which only has teeth present in the lower jaw. Fins are streamlined and sloped backwards. The body is usually light greyish, sometimes almost white, and is usually covered in a range of scars.
Risso’s Dolphin is named after Antoine Risso, a biologist and zoologist, born in 1777 in modern-day France, who also has a species of lanternfish, algae and snail named after him. Risso’s dolphin is one of the most mysterious cetacean species as a number of aspects of their behaviour and life cycle remains unknown.
Risso’s dolphin has a very wide distribution, being found in all of the major seas and oceans of the world, including the waters around the British Isles. They can be present in both temperate and tropical waters and only actively avoid the colder Nordic and polar regions. This species is generally found in deeper waters far away from land, but can occasionally be sighted near to the shore.
Life Cycle, Social Behaviour and Other Species
This species lives in pods of up to fifty individual animals, but pods of several hundred Risso’s dolphins have been sighted from time to time. Little is know about the social structure of Risso’s dolphin groups, but some pods appear to be made up of only female Risso’s dolphins and their young. Similarly, little is know about the reproduction of this species but the gestation period is thought to be over one year and females are believed to care for the young for a long period of time after birth. Like most other marine mammal species Risso’s dolphin communicate using sounds.
Risso’s Dolphin have been known to form pods with other species such as the common dolphin and the bottlenose dolphin. It has also been proven that Risso’s Dolphin can interbreed with other species – hybrid Risso’s/bottlenose dolphin have been sighted in the wild and born in captivity.
Risso’s dolphins have been successfully held in captivity, with a number of sea parks in Japan and the United States featuring Risso’s dolphins. Typically Risso’s dolphins are taken from the wild as calves and then brought up in captivity. This is a controversial practice with the taking of young thought to have a massive impact on the complex social structures of intelligent marine species
Squid is thought to be the main source of food for the Risso’s dolphin, with the majority of feeding being done at night when squid move up into shallower water. Smaller fish species and octopus may also be a key part of Risso’s dolphin’s diets in some parts of the world.
Scars and Unknown Social Behaviour
While some believe that the scars which cover the body of Risso’s Dolphin are caused by battles with squid it is now thought that they are actually caused by Risso’s Dolphin biting and scraping their teeth over each other. The exact reason why Risso’s Dolphins inflict these scars on each other remains unknown. It is theorised that it could be from play-fighting, competing with others for food or territory, mating conflicts or some other form of social interaction which humans have yet to understand. Risso’s Dolphin have also been observed breaching (jumping out of the water), chasing and ramming each other – behaviour which constitutes another form of social interaction which is yet to be fully understood.
Hunting and Conservation Status
Risso’s Dolphin are not hunted on anything other than a very minor scale, mostly by Japanese fishermen. The main threats to this species come from bycatch in commercial fishing nets and entanglement in fishing gear and pollution across some of their range. However, Risso’s Dolphin are thought to be relatively abundant in number and this, combined with the fact that their distribution is spread widely throughout the world’s seas, means that the IUCN (International Union for the Conservation of Nature) class Risso’s dolphin as a species of Least Concern on a global basis. In Europe, the numbers of this species are less clear, with the IUCN classing this species as Data Deficient in both the Mediterranean and Europe.