Risso’s Dolphin Profile
In Central Europe, to complement the Santa Claus legend, there’s the Jolly Old Fat Man’s antipode: a horned, shaggy, demonic creature, whose role is to go down the chimneys of the kids in Saint Nic’s black book – the naughty ones – and beat them with branches, eat them or take them straight to hell.
This terrifying servant of Santa is called Krampus, a name that is remarkably similar to the entirely unrelated, yet almost as mythical topic of today’s post: the Risso’s Dolphin, Grampus griseus.
Risso’s Dolphin Facts Overview
| Habitat: | Marine, coastal and off the coastal shelf |
| Location: | Worldwide except for the Black Sea and polar waters |
| Lifespan: | Up to 30 years in the wild |
| Size: | 2.6 to 5 m (8.53 to 16.40 ft) |
| Weight: | 300–500 kilograms (660–1,100 lb) |
| Colour: | Grey, mottled/scarred patterns |
| Diet: | Cephalopods, krill |
| Predators: | Unknown, likely sharks, perhaps orcas |
| Top Speed: | Unknown |
| No. of Species: | 1 |
| Conservation Status: | Least Concern |
Artistic (lazy) segues aside, Risso’s dolphin certainly looks like it’s been beaten with sticks.
This incredible creature, alone in its creepy genus, and little known, despite being one of the most common and largest animals in the ocean. These are unique in a number of ways, not least their ability to communicate.
Like pilot whales, these squid-eating cetaceans are deep divers and travel long distances from what appear to be feeding grounds to over-wintering sites.
In some of their range, they’re hunted enormously, even used as bait, and like all cetaceans, threatened by the fishing industry’s reckless and indiscriminate practices, but this species appears to be doing surprisingly well, regardless.
Interesting Risso’s Dolphin Facts
1. They’re unique
There are over 20 genera in the well-known Delphinidae, or dolphin, family, and this doesn’t include the related families of freshwater dolphins (of which there are four).
They range in size from the petite Hector’s dolphin at just over a metre long, to the monstrous, Orca, at up to nearly 10 metres in length and ten tonnes in weight.
Risso’s dolphin is a member of a single dolphin genus, Grampus, the etymology of which isn’t clear. They’re the only member of this mysterious genus, and are quite large for the family, at up to five metres long themselves.
But it’s not just their taxonomy that sets them apart; these dolphins have behaviours not seen in other members of the family, too, including some exceptional vocal abilities.
All members of the family are known for their ability to talk, but Risso’s have a wider range than most and can make vocalisations that are not heard from other species. Some of these include various barks and grunts.
They’re also able to emit sonar clicks with most of their heads out of the water, showing a level of control that isn’t known in other dolphins.
2. They’re very social
But even their social groups are unique. Dolphins typically have a chimp-like fission-fusion dynamic in their society where members bud off and join other groups quite loosely. If not this, then they usually have a matriarchal hierarchy instead.
Risso’s dolphins have a cluster system based on age and sex, with the strongest bonded groups consisting of adult males and females.
These societies collaborate to look after the offspring of any female, so mothers are able to wander off and get her nails did or otherwise look after themselves without jeopardising the safety of her calf.
A single pod of this species can consist of up to 4,000 individuals! And it’s not just conspecifics they hang out with.
They’ve been seen fraternising with other cetaceans like the white-sided dolphins and the most well-known species, the bottlenose.
They can get so chummy with the latter that they have been recorded forming hybrid offspring between the two species. 1
3. They move a lot
These large groups are physically active, both in terms of their interactions with one another and their movement as a group.
Adults are covered in scars, seemingly from the teeth of other members of the groups, but it’s not clear that this is from fighting, as much as it is from just enthusiastically interacting.
While they can talk, they also use chasing and biting, jumping out of the water, and various other physical behaviours as part of their social repertoire.
They can be aggressive, too, especially when harassing other species such as bottlenose dolphins and false killer whales.
But the majority of their time is spent travelling. They spend 77% of their lives doing this, compared with 13% socialising, and 5% feeding. The remainder is spent resting, which doesn’t leave them with many hours of sleep. 2
4. They’re deep divers
This species spends most of its time in deep water, just off the continental shelf. They like areas where the ocean dips down from 400 – 1000 metres, as long as it’s above about 10 °C.
Here, they engage in deep dives, as far as 600 metres down, where they forage for cephalopods, krill, and other crustaceans.
One of the most significant items in its diet is the widespread, yet little-known paper nautilus, or greater argonaut. This animal is neither a nautilus nor an ancient Greek sailor, but a bizarre species of octopus. 3
5. They’re migratory
Of course, these animals aren’t going around in circles during the 77% of their time spent travelling – they are incredibly rangy dolphins.
There isn’t a great deal of detail on their exact routes but population counts in California, for example, show an almost 10-fold increase in number in the Winter than in the Summer.
These immigrants are thought to have moved down from the cooler Northerly waters to spend Summer where it’s warmer, and other populations are known to follow the seasonal path of their food species, too.
This active lifestyle means the Risso’s dolphin really gets around. 4
6. They’re as common as muck
For such a little-known species, the Risso’s dolphin sure is common. It is likely the fourth-most abundant of all cetaceans in the Indian Ocean, after the common dolphin, the bottlenose, and the spinner; and it’s the second-most frequently spotted after the spinner around Tanzania.
Sri Lanka had somewhere between 5,500 and 13,000 of them when studied in the ‘80s, and their species is still listed as Least Concern by the IUCN, though more recent surveys are suggesting a decline in their number.
7. They’re hunted a lot
Cetaceans are the closest thing to people that we know of, living in the ocean, and their deliberate drowning, herding into nets and stabbing with knives and spears is unconscionable in any context outside of the most extreme desperation, and second only to the relentless massacres that occur in the name of “By-catch” by the global fishing industries.
Risso’s dolphins are killed in all of these ways, on top of their natural threats of orcas, sharks, and leviathans yet to be discovered by humanity.
Sadly, like so many others, they are caught in immense numbers as by-catch both on longline and in gill nets. They’re also hunted on purpose and threatened greatly by deep water sonar, such as is used by the militaries and in seismic surveys.
Mammals who dive deeply like the Risso’s dolphin are found with punctured ear drums from such events, and often race to the surface in a panic, getting decompression sickness in the process.
8. They’re contaminated
Like in many other species of cetacean, the mercury and other heavy metals that enter the ocean from land-based industrial waste, make their way up the food chain to the top predators and sit there as so-called reservoirs of toxicity.
Risso’s dolphins are another example of a contaminated food source, making their meat potentially dangerous to consume and also likely affecting the reproductive success of the animal in general.
Still, this hasn’t been enough to dangerously disrupt the species, yet.
On an individual level, these dolphins are faced with all of the above threats along with natural ones like killer whales, sharks and Cthulhu himself. So, it’s probably quite a frightening existence, but at the species level, it’s safe to say that Risso’s dolphin is doing very well.
This remarkably widespread species is found from the Southern tip of Argentina all the way to the Northern Faroe Islands and the Gulf of Alaska, and with any luck, will continue to thrive.
Risso’s Dolphin Fact-File Summary
Scientific Classification
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Family: | Delphinidae |
| Genus: | Grampus |
| Species: | griseus |
Fact Sources & References
- Kelsey Hans, “Grampus griseus Risso’s dolphin”, Animal Diversity Web.
- Deep Marine Scenes (2023), “Facts: Risso’s Dolphin”, YouTube.
- “Risso’s Dolphin”, NOAA Fisheries.
- “Risso’s Dolphin”, IUCN Red List.