Facts about Risso’s Dolphins
Little is known about this unusual looking dolphin. Their bodies become whiter as they age and accumulate scars. They can dive to depths of up to 300m.
Risso’s Dolphin identification
Risso’s Dolphins belong to a group called the Cetaceans, which includes all other dolphin species, as well as porpoises and whales. They are also members of Family Delphinidae, the so called Small Toothed Whales, which are also sometimes referred to as the true dolphins. The word dolphin is adapted from the word delphis which means fish with a womb.
Risso’s Dolphins get their common name from Mr. Risso, who first described the species in 1812. The scientific name Grampus griseus is derived from the word grisieus meaning grizzled (mottled with grey). The term grampus may come from the Latin words granis for large and piscis for fish.
These dolphins have a robust body. Their head is bulbous and lacks a distinct beak. They also have a distinct crease that runs up their forehead. The dorsal fin is situated mid way down their back and is tall and falcate. Like other toothed whales, delphinids have a single blowhole situated on the top of their head.
Risso’s are very light grey to white in colour; adults usually have many scars from teeth raking with other dolphins. They may also have marks caused by lampreys and cookie cutter sharks.
Risso’s Dolphin adaptations
Risso’s Dolphins can dive to depths of up to 300m, holding their breath for up to 30 minutes, although they usually only dive for 1-2 minutes at a time. The dentition of the Risso’s Dolphin is abnormal in that there is a low overall number of teeth (2-7 pairs) and they lack teeth on their upper jaw.
Where do Risso’s Dolphins live?
Risso’s Dolphins occur in temperate, tropical and subtropical waters (where temperatures range from 10 to 30°C). They are generally found in areas with depths greater than 1,000m, although they are known to inhabit shallower coastal areas in the waters off Northern Europe.
How big are Risso’s Dolphins?
How long do Risso’s Dolphins live?
Risso’s are estimated to live for at least 45 years.
What do Risso’s Dolphins eat?
The diet of Risso’s consists mainly of squid, although they may also eat other cephalopods such as octopus and cuttlefish, as well as fish and krill. Over 70% of the prey taken by Risso’s Dolphins are luminous or have cells that emit light called photophores, suggesting that they depend heavily on eyesight when feeding.
What eats Risso’s Dolphins?
Humans are the only known predators for this species.
Risso’s Dolphin life cycle and reproduction
Little is known about reproduction. However, we do know that breeding and calving can occur year round. The species also has a gestation period of 13-14 months.
Are Risso’s Dolphins endangered and if so why?
Risso’s Dolphins are listed as ‘Least Concern‘ by the IUCN. This means that they are not currently at risk of extinction.
The primary threat to Risso’s Dolphins is unintentional capture as bycatch from fishing gear. Risso’s Dolphins have also been directly hunted for their meat and oil in Japan, Indonesia, the Solomon Islands and the Caribbean. A small number of Risso’s have been taken from the wild for display in public aquariums.