Elephant Seal

A southern elephant seal bull can weigh 8,800 pounds, more than a pickup truck, and still dive over a mile deep and hold its breath for two hours.

They spend most of the year at sea, almost entirely underwater, surfacing for a couple of minutes between dives and sleeping as they sink.

Then they haul out on beaches, and the males fight. A breeding beach is one of the loudest, most violent gatherings of mammals anywhere.

There are two species, both in the genus Mirounga.

• Northern elephant seal (Mirounga angustirostris), along the Pacific coast of North America.
• Southern elephant seal (Mirounga leonina), around Antarctica and the southern oceans. This is the larger of the two and the largest seal in the world.

• Kingdom: Animalia
• Phylum: Chordata
• Class: Mammalia
• Order: Carnivora
• Family: Phocidae
• Genus: Mirounga

They are true seals, in the family Phocidae, which have no external ear flaps and cannot turn their hind flippers forward. That is why an elephant seal moves on land by humping along like an enormous caterpillar.

The name comes from the male’s inflatable nose.

Routinely 1,000 to 2,000 feet, and the deepest recorded dives pass 7,800 feet, around a mile and a half down. They hold their breath for 20 minutes to 2 hours.

The adaptations behind that are remarkable:

• Oxygen in the blood, not the lungs. An elephant seal exhales before diving and carries oxygen in its blood and muscles instead, which are unusually rich in it. Its blood makes up a far larger share of its body than ours does.
• Collapsible lungs. The lungs squash flat under pressure, so no nitrogen is forced into the blood and the seal avoids the bends.
• A slowed heart. The heart drops to just a few beats a minute while diving, and blood is diverted away from everything except the brain and heart.
• Almost no rest. They surface for only two or three minutes between dives and spend around 90 percent of their time at sea underwater.

They also sleep underwater. Elephant seals drift down in a slow spiral while asleep, hundreds of feet below the surface, in what researchers call sleep drifting. They get only around two hours of sleep a day at sea, which is among the least of any mammal.

The size difference between the sexes is among the most extreme of any mammal. A southern bull reaches 16 to 20 feet and up to 8,800 pounds. Females are 8 to 10 feet and 900 to 2,000 pounds, making a male up to eight times heavier than a female.

• The nose. Males grow an inflatable proboscis that develops from around age five. Inflated, it acts as a resonating chamber, turning his roar into something that carries across a crowded beach.
• Blubber. A thick fat layer for warmth in freezing water and as a food store during the months they fast on land.
• Eyes. Very large, for hunting in near-total darkness far below the surface.
• Whiskers. Highly sensitive, detecting the water disturbance left behind by swimming fish.
• Chest shield. Males develop thick, scarred, calloused skin on the chest and neck, armor built for fighting.

Northern elephant seals live along the Pacific coast from Alaska to Mexico, breeding on beaches and islands in California and Baja California.

Southern elephant seals live around Antarctica and on subantarctic islands including South Georgia, Macquarie and Kerguelen.

They are extraordinary travelers. Northern elephant seals make two long migrations a year, and a female may cover 11,000 miles annually, crossing open ocean alone and returning to the same beach she was born on.

They come ashore only twice a year: once to breed and once to molt.

Elephant seals are carnivores, eating squid, deep-sea fish, rays and small sharks.

Squid is the staple, and they hunt it in deep water where there is essentially no light. They find prey using those sensitive whiskers and their huge eyes, and some researchers think the faint glow of bioluminescent animals helps.

Then they stop eating entirely. Breeding bulls fast for up to three months on the beach, defending territory the whole time, and may lose a third of their body weight. Nursing females fast too, losing weight fast while pouring energy into a pup.

All of that comes out of blubber built up at sea. The entire breeding season runs on fat banked months earlier.

At sea, elephant seals are solitary. On land they gather in dense, noisy colonies.

Breeding beaches run on a brutal hierarchy. A dominant male, the beachmaster, controls a harem of dozens of females and fights off challengers. Bulls rear up chest to chest, roar through their inflated noses, and slam into each other, biting at the neck. Fights draw blood and leave permanent scars, and occasionally kill.

Most contests are settled by sound alone. Northern elephant seal males recognize each other’s individual calls and remember who beat whom, so a lesser male hearing a known beachmaster simply leaves rather than fight a battle he has already lost once.

Only a small fraction of males ever breed. The rest spend their lives at sea and never hold a beach.

Females give birth to a single pup after about 11 months, on the beach, in the middle of the colony.

The milk is extraordinary. Elephant seal milk reaches around 50 percent fat, richer than double cream, and a pup roughly quadruples its weight in under a month.

Then the mother leaves. After about 28 days she returns to sea, and the pup is on its own. It lives off its fat on the beach for several weeks, teaching itself to swim in shallow water, before heading out to the open ocean with no guidance at all.

Many do not survive the first year. Those that do live 14 to 20 years, with males dying younger because of the fighting.

Great white sharks and orcas are the main predators, and both concentrate around breeding beaches when seals are coming and going. Leopard seals take pups in the south.

Historically the threat was whaling and sealing. Elephant seals were hunted relentlessly in the 1800s for the oil rendered from their blubber, and both species were driven to the brink.

Today’s pressures are fishing gear entanglement, plastic, disturbance at breeding beaches, and the effect of warming oceans on the deep-sea prey they depend on.

Both species are listed as Least Concern today, and the northern elephant seal is one of the most dramatic recoveries in conservation history.

By the 1890s hunting had reduced it to perhaps 20 to 100 animals, all on one island off Mexico. It was believed extinct more than once. Protection by Mexico and later the United States allowed it to rebuild, and there are now well over 200,000.

There is a lasting cost. Every northern elephant seal alive descends from that tiny surviving group, so the species has very little genetic variation, which leaves it more exposed to disease than its numbers suggest.

Elephant seals are major predators of deep-sea squid and fish, and they are one of the few animals linking the deep ocean to the surface world. Nutrients they bring up and release in shallow water feed coastal systems.

They are also prey, supporting white sharks and orcas, and the carcasses and afterbirth left on breeding beaches feed gulls, vultures and scavengers.

They have turned out to be excellent scientists. Researchers fit elephant seals with small sensors that record depth, temperature and salinity, and the animals then collect data from parts of the deep Southern Ocean that ships rarely reach. A great deal of what we know about water conditions under Antarctic ice was gathered by seals wearing instruments on their heads.