This dolphin looks like someone ice-skated all over it.
As an adult, its greyish-black skin can have such extensive scarring it almost looks white, and we can even use photo recognition software on it. They’re pretty impressive markings considering they’re made by something with no top teeth. In both cases.
Males, for example, use their 2-7 pairs of bottom teeth to playfully and/or aggressively rake each other in skirmishes or just in passing. It also takes time out to harass other species like bottlenose dolphins or the similar-looking false killer whale, but that’s not the only reason for its wounds.
A bit squiddly-fiddly
The life of a Risso’s dolphin is full of ups and downs, including those found in oceanic geography.
Usually feeding at night, it’s mostly spotted near continental shelves, slopes, or over undersea canyons pretty much anywhere except the polar regions. It can dive as deep as 1,000 metres (3,280 feet) and for up to 30 minutes, which is pretty handy when its favourite prey prefers a deeper, darker swim.
Squid species, including the weird half-shell-half-squid argonauts are top of its menu, and they can get rather handsy when trying to escape death – hence a lot of the scarring. Cookie-cutter sharks also try their luck from the other end of the food chain, but the Risso’s life isn’t all about the fight.
An incredibly social dolphin, it’s been seen in mega-pods of up to 4,000, and although males and females with calves are generally segregated, they seem to form long-term bonds within their own groups.
Female pods tend to be bigger, so there are more babysitters around, and male pods smaller so there are fewer rivals. In a social group communication is key, and according to Pavan and Borsani, although Risso’s dolphins may not seem as vocal as other dolphin species, their whistles and clicks are distinctive and unique. In Phillips et al.’s opinion, this may be linked to the vertical dent in their foreheads giving them a more angled sonar beam.
It can also click even when most of its head is above water, although that might be the equivalent of nonsensical human gargling. It may seem different to, and sometimes antagonistic to other dolphin species, but again, it might just be its way of saying it likes them.
Hybrids of Risso’s and bottlenose dolphins have been recorded, both in the wild and captivity, so it’s not just cabin fever, and it’s occasionally been seen swimming peacefully alongside them as well as grey whales.
A particularly famous Risso’s dolphin even ingratiated himself with humans in the 19th century.
I mentioned earlier that Risso’s dolphin is found almost everywhere except the polar regions, but it’s pretty rare around New Zealand. That was the first thing that made “Pelorus Jack” stand out from the crowd back in 1888.
The second thing was his penchant for escorting boats from Pelorus Sound over to the edge of French Pass, a particularly hazardous stretch of water with waves approaching 8 knots. Following boats to and from the area, he enjoyed riding the bow waves and became something of a celebrity, to the point that 19th-20th century literature heavyweights Mark Twain and Frank T. Bullen ventured over to see what all the fuss was about.
Of course, celebrities and friendly animals quickly find themselves in the firing line, and also sometimes literally.
An unknown party fired at Pelorus Jack from their steamboat. Fortunately he survived, and his popularity was such that people lobbied for his protection under the Sea Fisheries Act of 1894 and Fisheries Act of 1908. Unfortunately said legal protection only officially extended to seals, but was renewed twice anyway. The jury’s still out as to whether it helped, because Pelorus’ fate is something of a mystery.
One theory claimed he was harpooned by visiting Norwegian whalers. Another, following a death-bed confession from one of the men, was that he was killed after being stranded by a storm. The theory that seems most likely is that he died of old age and was washed up on a beach; he escorted boats up and down for a good 24 years, and the lifespan of Risso’s dolphin hovers around 30.
However, he was not forgotten, and was immortalised in both a chocolate bar and a Scottish dance. Who wouldn’t be happy with that?
In some parts of Europe, it’s Risso’s dolphin that carries a little bit of human memory inside it, and it’s not a good thing.
Difficult to digest
At a quick glance, a plastic bag can look like a tasty squid, or appear as something tasty to said squid or other prey item, and it’s one of the worst things to have in your stomach. Pesticides and other horrible industrial chemicals or PCBs can also hitch an interior ride, especially if you’re cruising the Mediterranean.
Over in Asia, Risso’s dolphin is still actively hunted, both in the Philippines, Sri Lanka, and the infamous Taiji dolphin drive hunt in Japan every year. If it’s not sold as meat, it’s for fertiliser, or equally demeaning – as a performing animal. But don’t worry – we have taken a few steps to redeem ourselves.
For example, Risso’s dolphin and its cohorts used to come a cropper in purse-seine nets used for tuna fishing. In 1988, the International Marine Mammal Project made some noise (and deeply upsetting videos) about the millions of dolphins caught in the cross-fire, and by 1990, had set up the Dolphin Safe Tuna Program. (If you’re partial to a bit of tuna, you’ve probably spied their logo on the side of the tin.) The result? A 99% drop in dolphin deaths from tuna nets, hoorah!
Risso’s dolphin is also a European Protected Species, so it can’t be hunted or captured, and the Whale and Dolphin Conservation Society is lobbying for its own protected area around the Isle of Lewis in Scotland, a known area for calving and feeding.
Since it sensibly keeps out of our way and prefers deeper water, Risso’s dolphin is still a bit of a mystery. It seems to like giving itself scars, but we shouldn’t try to add to them. What it does in the comfort of its own home is none of our business.
Latin: Grampus griseus
What? The largest marine mammal with “dolphin” in its name.
Where? Tropical and temperate waters worldwide, from 400-1,000 metres / 1,312-3,280 feet deep.
How big? From 2.6-4 metres / 8.5-13 feet long
Endangered? Provisionally Least Concern due to its large range, but there’s a bit of a question mark over its population status.
Probable motto: I like you, and that’s the tooth.
They look cute. Do they need my help at all?
Due to its Least Concern badge, Risso’s dolphin doesn’t have any specific campaigns at the moment. However, it’s threatened due to accidental bycatch, noise and chemical pollution, and commercial hunting.
Just to prove I’m not fibbing:
2009. “Trace elements and vanadium in tissues and organs of five species of cetaceans from Italian coasts“, Chemistry and Ecology, 25(5):311-323.
Bellante, A. et al. 2012. “Stranded cetaceans as indicators of mercury pollution in the Mediterranean Sea“, Italian Journal of Zoology, 79(1):151-160
Bellomo, Stefano. No date. “Understanding the Risso’s dolphin’s scars“. Oceanographic.
2010. “A near mass stranding of cetaceans in St Helena Bay, South Africa“, African Journal of Marine Science, 32(1):163-166.
2013. “A Veterinary and Behavioral Analysis of Dolphin Killing Methods Currently Used in the “Drive Hunt” in Taiji, Japan“, Journal of Applied Animal Welfare Science, 16(2):184-204.
“Dolphin safe fishing“. No date. International Marine Mammal Project.
Drysdale, Neil. 2019. “New report calls for greater protection of Risso’s dolphins in the Western Isles“. The Press and Journal.
Editors of Encyclopaedia Britannica. No date. “Grampus“. Britannica.com.
Hans, Kelsey. No date. “Grampus griseus“. Animal Diversity Web.
Hartman, K.L. et al. 2008. “Social structure of Risso’s dolphins (Grampus griseus) at the Azores: a stratified community based on highly associated social units“, Canadian Journal of Zoology, 2008, 86(4): 294-306.
Hutching, Gerard. 2006. “Dolphins – Humans and dolphins“, Te Ara – the Encyclopedia of New Zealand.
Kiszka, J. & Braulik, G. 2018. “Grampus griseus. The IUCN Red List of Threatened Species” 2018: e.T9461A50356660.
Naish, Darren. 2012. “Grampus griseus joins the globicephalines“. Scientific American.
1997. “Bioacoustic research on cetaceans in the Mediterranean Sea“, Marine and Freshwater Behaviour and Physiology, 30(2):99-123.
“Risso’s dolphin“. No date. Cetacean Search and Rescue Unit.
“Risso’s dolphin“. No date. Hebridean Whale & Dolphin Trust.
“Risso’s dolphin“. No date. Monterey Bay Aquarium.
“Risso’s dolphin“. No date. Scottish Natural Heritage Trust.
“Risso’s dolphin“. No date. Whale and Dolphin Conservation Society.
Featured image credit: “Risso’s dolphin, Grampus griseus“, by J. Maughn.