Southern Elephant Seal

Genuinely enormous

Numbers do not really convey this animal, but here they are anyway. A big male southern elephant seal measures somewhere between fourteen and nineteen feet long and weighs up to about four tonnes. That is heavier than a pickup truck, in an animal that can still move fast enough on a beach to catch a person who has misjudged the distance.

Females are a completely different proposition, running eight to ten feet and four hundred to nine hundred kilograms. A bull can be ten times the mass of a female, which is one of the most extreme size differences between sexes of any mammal on Earth. The name comes from the male's inflatable proboscis, a great pendulous nose he uses as a resonating chamber to roar.

Deeper than most submarines are rated to go

Elephant seals routinely feed at 400 to 800 meters, holding their breath for twenty to thirty minutes at a time. That alone would make them exceptional. But the record is astonishing: a bull southern elephant seal has been tracked to 2,388 meters, close to a mile and a half straight down, and individuals have stayed submerged for around two hours.

They also do it relentlessly. At sea, an elephant seal dives almost continuously, surfacing for only a few minutes between dives, day and night, for months on end. They spend the overwhelming majority of their lives underwater and in the dark, hunting squid and fish in the deep scattering layer.

The beachmasters

Once a year the ocean life stops and the beach life begins. Bulls haul out on subantarctic islands like South Georgia and Macquarie and fight for control of stretches of shoreline and the females on them. A winning male, called a beachmaster, may hold a harem of dozens of females, and a small number of males father the overwhelming majority of the pups.

The fights are serious. Two bulls rear up chest to chest, several feet of body lifted off the sand, inflate their noses, roar at a volume you can feel, and slam down onto each other, tearing at the neck with their teeth. The thick, scarred, calloused chest shield each mature bull carries is armor built for exactly this. Most disputes are settled by display and posture, because the stakes of an actual fight are high enough that both animals prefer to avoid it.

Throughout the entire breeding season a beachmaster does not eat. He may hold the beach for two months, burning through his own blubber the whole time, and lose a third of his body weight before returning to the sea.

The fastest childhood in the ocean

A female gives birth to a single pup weighing around forty kilograms. She then nurses it for about three weeks on milk that becomes extraordinarily fatty, in some stages more than 40 percent fat, richer than heavy cream.

The pup roughly triples or quadruples its weight in those three weeks, ballooning into a round, wide-eyed animal often called a weaner. The mother, meanwhile, is fasting the entire time, converting her own body directly into her pup.

Then she leaves, abruptly, and returns to sea. The weaner stays on the beach alone for another several weeks, living off the fat it just accumulated, teaching itself to swim in shallow pools and tide margins. Nobody instructs it. When the blubber runs low enough, it goes to sea and starts diving, and either learns to hunt in time or does not.

Hunted to the brink, and back

In the nineteenth century elephant seals were killed in staggering numbers for their blubber, which rendered into a high-quality oil. Whole populations were wiped out. The northern elephant seal, a separate species off California and Mexico, was reduced to perhaps a few dozen individuals and was believed extinct at one point before a tiny remnant colony was found.

Legal protection changed the story. Both species recovered dramatically through the twentieth century, and southern elephant seals now number in the hundreds of thousands and are listed as Least Concern. It stands as one of the more encouraging marine conservation outcomes on record.

There is a lasting scar, though. The northern species passed through such a severe genetic bottleneck that today's animals, however numerous, carry very little genetic diversity, which can leave a population more vulnerable to disease and to environmental change. You can restore the numbers. Restoring the variation is a much longer proposition.