South American Fur Seal

The seal nobody had counted

This species runs the entire coastline of South America, from Peru south through Chile, around Cape Horn and back up through Argentina and Uruguay to southern Brazil, plus the Falkland Islands, also known as the Malvinas. For decades everyone agreed that Uruguay held most of them.

Then in January 2018 Baylis and colleagues flew drones over the Falklands and counted the pups. There were 36,425 of them, against fewer than eight thousand counted the same way in Uruguay.

One survey. It roughly doubled the known Atlantic population of the species and moved its headquarters about fifteen hundred kilometres. Nothing about the seals changed that January. Only what we knew about them did.

It is a good lesson in how conservation numbers actually work. The Falklands are hundreds of scattered islands, and most of these colonies sit on cliffs and boulder beaches you cannot walk to. Until small drones got cheap, there was no practical way to count them, so nobody had.

Which leaves the official world figure looking old. The last full IUCN assessment, from 2016, puts the species at somewhere around two hundred thousand animals, and its own pages do not quite agree with each other on that. Everybody now treats it as too low anyway, and a fresh assessment is under way. Until it arrives, the honest answer is that there are more of these seals than we thought and nobody can yet tell you how many more.

Sealing, from 1775 to 1991

The record starts early. In 1775 a ship out of Boston called the States left the Falklands loaded with 13,500 skins. The islands were worked hard for the next century and a half.

By the time somebody sat down and counted, in January 1920, there were 5,500 seals of every age left in the whole archipelago. The Falkland Islands Government stopped handing out sealing licences the following year. Getting from that low point to the drone survey is one of the quieter comeback stories in this family, and nobody wrote it up while it was happening, because nobody was watching.

Uruguay went the other way and kept going longer than anybody on Earth. Between 1965 and 1991 the harvest there took 234,000 fur seals. Writing in 1993, the FAO called it the longest running sealing operation anywhere in the world, and by then it had only just stopped.

There was an uglier chapter too, one that never went in any official record. Through the 1970s and into the 1980s, fur seals were shot illegally in southern Chile and Argentina, chopped up and dropped into traps as bait for the king crab fishery. The best estimate of how much seal went into those traps runs to hundreds of tonnes a year.

Air, not fat

Look closely at the skin and you find bundles: one thick guard hair with 35 to 40 fine underfur hairs packed beneath it, all emerging through a single opening. On a dive the outer coat wets through, but a layer of air stays sealed against the skin. That air does the insulating. A fur seal carries proportionally less blubber than a true seal, so the coat is not a luxury, it is the survival system, and anything that ruins it, oil above all, is lethal.

Everything else about the body says eared seal. The ear flaps are long and prominent, and in females and older subadults there are often lighter patches around them, along with a band of paler colour wrapping the lower neck, which is the single most useful field mark on this species. The fore flippers are longer and narrower than in most other fur seals, and they are the engine: an eared seal swims by flapping its front limbs like wings, while a true seal drives with its hind end. Those hind flippers rotate forward under the body instead, so a South American fur seal walks, climbs and scrambles over the boulder beaches and cliff bases where it breeds.

The whiskers are creamy white and only short to moderate in length, which is a useful contrast with the Antarctic fur seal's very long, conspicuous ones. Pups are born black and moult to a lighter brown grey at three to four months.

El Niño on the Peruvian coast

The Peruvian seals live along one of the richest coastlines on Earth. Cold water wells up from the deep there, carrying nutrients with it, and fish stack up on top of that. El Niño switches the whole thing off.

When it does, the seals starve. The El Niño of the early eighties killed every single pup born that year, the entire year group, without exception.

The next big one, in the late nineties, was measured properly. A census counted about twenty four thousand seals before it arrived. Two years later the same count found about eight thousand.

Two thirds of them, gone. The way it happened is simple and horrible. With the fish scattered, mothers had to stay out at sea for ten days or more at a stretch just to find a meal, and their pups, waiting on shore with nothing to drink, starved before they got back. So few animals came through that you can still read the dent they left in the species' DNA.

You will see that crash quoted three different ways on three different websites. The version on this page is the one tied to two real censuses with dates attached, which is why it is the one we use.

Food is a competition problem here as well. In Peru these seals eat anchoveta, the same small fish that feeds one of the biggest fishing industries on the planet, and the fleets have repeatedly hauled the anchoveta down to very low levels. In the Falklands the key prey is lobster krill, and the seals' main hunting ground sits directly on top of the thickest of it.

The Peruvian and northern Chilean seals, roughly twenty one thousand of them, are assessed separately from the rest of the species and listed as Vulnerable.

Mothers who nurse three offspring at once

Most fur seals stop nursing a pup somewhere between four months and a year old. Peruvian South American fur seals do not work to a timetable like that. Weaning here can happen at six months or it can take three years, and a mother will feed a yearling and a newborn at the same time.

Now and then one has been recorded feeding three at once: a newborn, a yearling, and an older brother or sister already two or three years old and still queueing up for a meal.

This is an unpredictable coastline, and flexibility is the answer to unpredictability. In a good year a pup grows fast and leaves. In a bad year it stays, and the mother carries it through.

The rest of the schedule is standard for the family. A female comes ashore, gives birth, and mates again within a few days. Then she settles into a rhythm of four or five days out at sea hunting and a day or two back on land with the pup.

The clever part is a pause. After she mates, the tiny new embryo simply stops and waits for three or four months before it attaches and starts growing. Add that pause to eleven months of actual pregnancy and you get a birth on almost exactly the same date every year.

In Uruguay the mating system is a lek, which means the males hold small display patches and the females wander wherever they please. No male gets to fence a group of them in. Among fur seals that is unusual.