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Ribbon Seals: Stunning on the Outside, Bizarre on the Inside

The views expressed are those of the author and are not necessarily those of Scientific American.


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ribbon seal

Credit: Josh London (NOAA)

Look at this guy. So casual. People pay money to look this casual. Just out on the ice in his black and white pyjamas. Waiting for his mulled wine and hard cheeses. Look at him.

Meet the ribbon seal (Histriophoca fasciata), the most striking and handsome of all the world’s pinnipeds, found in the icy waters off the southern coast of Russia and to the north of Korea and Japan.

Both the males and females sport the glorious banded pelt, but the females are slightly less glorious in their white-on-brown variation. Every ribbon seal is patterned with four white bands – one around the neck; one around each of the front flippers; and one around the lower back, just before its hind-flipper – but their size and exact location will differ from seal to seal. This has led some researchers to suggest that the variations might help ribbon seals to identify each other when they’re looking for mates. Another theory regarding their distinctive patterning is that it could help to break up and disguise the shape of the seal’s body when seen from far away, blending it into the shadows and sharp-edged mounds of ice that surround it on the ice floes.

For years, anywhere from 6,500 to 23,000 ribbon seal pelts, along with the animal’s flesh and oils, were sold annually by the Russians, but since the collapse of the Soviet Union 1991, commercial hunting has largely come to a halt.

ribbon-seal-pups

Ribbon seal pups being very friendly. Credit: (L) Josh London (NOAA) (R) Heather Ziel (NOAA)

And the babies? The babies look like soft, velvety clouds of unbridled joy and obesity. Newborn, they weigh in at around 9.5 kg, and over the next 3-4 weeks, they’ll gain an extra 20 kg or so. After a month, they’ll be completely abandoned by mum on an ice floe, right when they’re so fat they can barely swim. So they’ll spend the next three weeks living off nothing but their fat stores while they teach themselves how to survive. It usually takes another two months before a ribbon seal pup can swim as proficiently as the adults, and it’ll start off hunting small crabs and prawns before working its way up to the species’ preferred diet – walleye pollock (Theragra chalcogramma), eelpouts (Zoarcidae), and magistrate armhook squid (Berryteuthis magister). As adults, ribbon seals will need to eat around 9 kg of food each day.

At around five weeks old, ribbon seal pups will moult away their thick, grey coats to reveal the stripy pyjamas beneath, and these will continue to develop over the next three years as the seal approaches sexual maturity. Adult females can usually only birth one pup per year.

Male ribbon seal

Adult male ribbon seal peeks over the edge of a ridge on an ice floe after release. Credit: Josh London (NOAA)

It’s not just the stripy coats that make ribbon seals entirely unique – their insides are bizarre too. In all males, and some females and juveniles, a delicate air sac is attached to the lower end of the trachea. No one really knows what it does, but it could have to do with providing extra buoyancy in the water, or perhaps it helps the seals to vocalise to one another. They also have the biggest internal organs (relative to body weight), plus the highest volume of red blood cells and haemoglobin, of all known seal species. Combined, these features could help the species cope with having to dive up to 600 metres below the surface in search of food. That higher storage capacity for oxygen in the blood and the lungs is probably a lifesaver.

Ribbon seals don’t have the best eyesight, but they don’t seem that fussed about what’s going on around them anyway. They’re pretty easy to sneak up on, they pay little attention to incoming boats or humans, and the mothers are cool with leaving their week-old pups alone on the ice for long periods of time. It’s possible that this general lack of awareness points to the fact that ribbon seals don’t seem to have any natural predators. So they’re basically the blue-footed boobies of the Arctic. In a 2008 status review of the species for the National Oceanic and Atmospheric Administration (NOAA), it was concluded that:

“There is little or no direct evidence of significant predation on ribbon seals and they are not thought to be a primary prey of any predators. Polar bears and killer whales may be the most likely opportunistic predators in the current sea ice regime, but walruses could pose a potentially greater risk if reduced sea ice conditions force these pagophilic [existing in ice] species into closer proximity in the future.”

Turns out the only active predators of ribbon seals are humans, but fortunately this has been toned down in recent decades.

There are three populations of ribbon seals – two in the Sea of Okhotsk and one in the Bering Sea – but no one quite knows how many ribbon seals there are in these populations. It’s been more than more than three decades since the last official survey came up with an estimate of 450,000 to 500,000 individuals in the wild, but more recently, researchers have suggested that the numbers could be anywhere from over 200,000, to more than 500,000, because with no natural predators and drastically reduced instances of hunting, it’s reasoned, they should be increasing in numbers. However, they are an entirely ice-dependent species, so who knows what climate change will mean for these guys in the future. The IUCN Red List currently lists the species as “Data Deficient”.

Here’s a video of a curious ribbon seal who strayed all the way to Squamish in Canada:

Related posts:

World’s rarest whale seen for first time: Spade-toothed whale

Thresher sharks tail-slap sardines into oblivion

Lumpsucker Fish: Just When You Thought the Ocean Couldn’t Get More Lumpy and Adhesive

Bec Crew About the Author: Bec Crew is a Sydney-based science writer and award-winning blogger. She is the author of 'Zombie Tits, Astronaut Fish and Other Weird Animals' (NewSouth Press). Follow on Twitter @BecCrew.

The views expressed are those of the author and are not necessarily those of Scientific American.





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