Histriophoca fasciata
The most boldly marked seal alive, wearing a pattern nobody has been able to explain.
The ribbon seal's pattern is unique among mammals. Four crisp white bands on a near-black body: one collar around the neck, one broad band around the hips and tail, and one closed ring around each foreflipper, so the flipper sits inside a white loop. It is not camouflage, it is not a warning colour, and it does not match any signalling system anyone has identified.
The contrast depends on who is wearing it. Adult males are the extreme version, deep black with near-white bands. Females carry the same layout in silvery-grey and warm brown, so the bands read as pale smudges rather than paint. Juveniles have almost nothing.
The pattern builds slowly. Pups are born white, moult to a plain blue-grey and silver, and then with each annual moult over the next few years some patches darken and others lighten until the ribbons resolve. A ribbon seal does not look like a ribbon seal until roughly its fourth year, which means a young animal and an adult male in the same photograph look like two different species. Because the bands vary slightly between individuals, some researchers use them for photo identification the way tiger stripes or whale flukes are used. What the pattern is actually for remains one of the more honest gaps in marine mammal biology.
Ribbon seals have an anatomical feature no other seal has: a large inflatable air sac connected to the trachea, running back over the ribs on the right side of the body. It is much larger in males than in females.
Its purpose is not settled. The leading idea is sound production, because male ribbon seals make loud downward-sweeping underwater calls during the breeding season, and an air sac would let a seal recycle air instead of losing it with every call. A second idea is buoyancy, letting the animal hang at the surface or hold its position in the water column without effort. Both could be true at the same time.
The sexual dimorphism is a strong clue. When a structure is much bigger in one sex and appears at maturity, it usually has something to do with competition for mates, which points toward the sound explanation. But "probably" is as far as the evidence currently goes.
Most true seals move on land by humping forward like a caterpillar, driving with the belly and chest. Ribbon seals do something else. They undulate the whole body in a snaking motion while gripping the ice with the claws of the foreflippers and pulling with alternating strokes, left, right, left, swinging the head and hips from side to side.
It is fast, and it is highly specialised. Observers have noted that the same movement fails completely on other surfaces, apparently because friction between the fur and anything other than smooth ice is too high. A ribbon seal on a wooden dock is a much less impressive animal than a ribbon seal on a floe.
There is a related oddity. Ribbon seals are notably unbothered by people or vessels approaching them while they are hauled out, in sharp contrast to ringed seals, which flee instantly. NOAA links this to predation pressure: ribbon seals breed far offshore in ice that polar bears and Arctic foxes rarely reach, so the escape reflex was never needed and never developed.
For most of the year, nobody knows where ribbon seals are. They haul out on pack ice in spring to give birth, nurse and moult, and once the moult is finished they leave the ice entirely. They do not use shorefast ice, and they are almost never seen on land. They spend the rest of the year alone in the open North Pacific.
That makes them one of the least observable seals in the northern hemisphere. Most of what is known about their diet, which includes pollock, eelpout, Arctic cod, squid and crustaceans, comes from spring samples, which is exactly the season when they are eating least. What a ribbon seal eats in October is largely guesswork.
Occasionally one turns up somewhere it has no business being. Healthy ribbon seals have been recorded as far south as Squamish in British Columbia, Long Beach in Washington, and Morro Bay in California, and one young adult spent time hauled out on docks in inland Washington. None of these animals showed signs of illness. They had simply kept swimming.
Ribbon seals need pack ice within a narrow window. Pups are born far offshore over roughly five to six weeks from April into early May, most are weaned by mid-May, and mothers mate again shortly afterward. The whole reproductive cycle is compressed into the period when the Bering and Okhotsk ice is already retreating.
That timing is the vulnerability. It is not the total amount of ice that matters most, but whether suitable floes are in the right place at the right moment. Ice that breaks up two weeks early can separate mothers from pups that are not yet weaned.
The US National Marine Fisheries Service reviewed the species twice for Endangered Species Act listing. It was made a Species of Concern, a lawsuit followed in 2009, and in July 2013 NMFS concluded again that listing was not warranted. The IUCN still lists the species as Least Concern on its 2016 assessment, with the population likely somewhere at or above 200,000 to 300,000 animals and the trend recorded as unknown. That last word is doing a lot of work.
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