Mirounga angustirostris
Declared extinct in the 1880s. Every one alive today descends from the handful that were missed.
In the nineteenth century, northern elephant seals were hunted for the oil rendered out of their blubber. A single large bull yielded a great deal of it, and the species was killed along the whole coast, colony after colony, until by the 1880s it was believed to be extinct.
It was not, quite. A tiny remnant survived on Isla Guadalupe, a remote island off Baja California. Estimates of how many animals actually came through that bottleneck range from a few dozen to fewer than a hundred, and some accounts put it as low as around twenty. Nobody can be certain, because there was nobody there counting. What is certain is that every northern elephant seal alive today, all two hundred thousand and more of them, descends from that one group.
Mexico gave the species legal protection in 1922 and the United States followed. Numbers climbed steadily through the twentieth century. Seals recolonised beaches they had not touched for a hundred years, and today NOAA's US stock assessment gives a conservative minimum of about 85,000 animals, with roughly 80 percent of the US population at the Channel Islands. Range-wide figures including Mexico are usually put somewhere above 200,000, with a commonly cited recent census figure of about 239,000. The trend is upward.
The recovery is one of the clearest successes in marine mammal conservation. It is also one of the clearest demonstrations that saving a species late is not the same as saving it in time.
The bottleneck is visible in the genome. Northern elephant seals have strikingly low genetic diversity compared with other seals, which is exactly what population geneticists predict after a population is squeezed through a very small number of survivors. All the variation carried by the animals that were killed is gone permanently. Protection stops the killing, but it cannot put back genes that no living animal is carrying.
That matters for the future. A population that is genetically uniform has fewer options if a new disease arrives, because there is less chance that some individuals happen to carry resistance. Two hundred thousand seals is a healthy-looking number sitting on a narrow genetic foundation.
An elephant seal at sea dives more or less continuously, typically to 300 to 800 metres for 20 to 30 minutes at a time, then surfaces for only two or three minutes before going back down. The deepest recorded dives exceed 1,500 metres, with a record near 1,735 metres, and long dives can approach two hours. They spend around nine months of the year at sea and almost all of it underwater, which is why so few people ever see one away from a breeding beach.
Doing this requires a body organised entirely around oxygen. Elephant seals carry a very large blood volume for their size, loaded with haemoglobin, and their muscles are dense with myoglobin, which is why seal meat is so dark. An enlarged spleen holds a reserve of oxygen-rich red blood cells and releases them during a dive. On the way down the lungs collapse deliberately, pushing air out of the parts where gas exchange happens, which reduces the risk of nitrogen problems. Heart rate slows dramatically and blood is redirected away from the extremities toward heart and brain.
Much of the hunting happens in the oxygen minimum zone, a mid-water layer where dissolved oxygen is so low that most large fish stay out. Squid and mesopelagic fish that tolerate it gather there. A predator that can hold its breath for half an hour gets to raid a pantry its competitors cannot enter.
Until recently, nobody knew when elephant seals sleep. They are at sea for most of the year, they cannot doze at the surface without becoming easy work for great white sharks and killer whales, and they dive almost constantly.
In 2023 a team led by Jessica Kendall-Bar published results in Science from seals fitted with EEG recorders that measured brain activity directly. The seals sleep while diving. They swim down to around 300 metres, stop swimming, and drift. As sleep deepens and muscle tone is lost, the animal rolls over and sinks slowly upside down in a spiral, which the researchers named a sleep spiral, then wakes and swims back up.
The naps run about ten minutes each, and the daily total comes to less than two hours for months on end. Among mammals, only elephants are known to sleep so little. The logic holds: the safest bedroom available to an elephant seal is a few hundred metres below the sharks.
The breeding season inverts everything about their lives. From December to March the seals crowd onto beaches, and none of them eat. Bulls arrive first and fight for position, rearing up chest to chest and slamming down with open mouths, which is what the thick calloused chest shield is for. The winners control access to groups of females, and a small number of males end up fathering most of the pups. A big bull can exceed four metres and approach 2,000 kilograms, three to four times the mass of the female he is mating with.
The famous nose is a resonator. A bull inflates it and produces a slow, percussive, drum-like roar that carries down the beach. The calls are individually distinctive, and males learn to recognise specific rivals by sound, which means a great deal of the conflict gets settled without anybody bleeding.
Females give birth within days of arriving, nurse for about a month on milk that can exceed 50 percent fat, mate again, and leave. NOAA records that fasting elephant seals can lose up to 36 percent of their body weight over a breeding season. The weaned pup, black coat now moulted to sleek silver, sits on the beach for weeks living off its own fat, then teaches itself to swim, dive and hunt with no instruction at all.
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