Steller's sea cow

Name and taxonomy

The common name honours Georg Wilhelm Steller, the naturalist who described the living animal. Eberhard von Zimmermann gave the species its first formal name, Manati gigas, in 1780. Anders Jahan Retzius moved it into a new genus, Hydrodamalis, in 1794. Johann Karl Wilhelm Illiger placed it in the genus Rytina in 1811, and many writers used that name. Theodore Sherman Palmer first used the current combination Hydrodamalis gigas in 1895.

The species belonged to the order Sirenia, the sea cows, and to the family Dugongidae. Russian hunters called it the cabbage-eater, because it grazed the kelp they knew as sea cabbage. Its rough hide earned it the nickname bark animal, and several European languages still call it that. GBIF lists the English name great northern sea cow as well.

Evolution and relatives

Hydrodamalis and its sister genus Dusisiren form the subfamily Hydrodamalinae. This line split from the other sirenians about 4 to 8 million years ago. Its ancestors lived on warm mangrove coasts before they moved into the cold North Pacific. Steller's sea cow descended from the Cuesta sea cow, Hydrodamalis cuestae, which lived off California. The Cuesta sea cow probably died out when the Quaternary ice ages cooled the oceans. One lineage adapted to the cold and became Steller's sea cow.

Over time the genus grew larger and lost both its teeth and its finger bones. The dugong, Dugong dugon, is the only living member of the family Dugongidae. It is therefore the closest living relative of Steller's sea cow, though it reaches only about 3 metres. Genetic work shows that the sea cow converged with other marine mammals in genes for metabolism and immunity.

Appearance

Adults were reported at 8 to 9 metres long, far beyond any living sirenian. Steller measured one female at 7.5 metres, and Domning later estimated an upper limit of about 7.9 metres. Published weight estimates run from 5,400 to 11,196 kilograms, with an average near 8,000 kg. Steller himself wrote down two conflicting weights, 4 and 24.3 tonnes. The body was rounded and swollen at the belly and tapered towards the head and the tail.

The head was small and short, with tiny eyes and no external ears. The skin was brownish-black, and some animals carried white patches. Its outer layer was about 2.5 centimetres thick and rough like tree bark on the sides. Under the skin lay 8 to 10 cm of blubber against the cold. The forelimbs were short, hooked and about 67 cm long, and the tail ended in a forked fluke.

The mouth had no teeth at all. Instead, the upper lip carried a mat of white bristles about 3.8 cm long, and two horny plates ground the food. Stiff bristles 10 to 12.7 cm long also stood out from the muzzle. Domning found no evidence that males and females differed in size.

Habitat and range

When Steller found it, the species lived only in the shallow seas around the Commander Islands. These islands, Bering and Copper, lie in the Bering Sea between Kamchatka and Alaska. The animals stayed in cold, shallow coastal water rich in kelp and seaweed. Herds gathered near the mouths of streams, which suggests they needed fresh water to drink. They floated so close to shore that hunters could wade out to them.

Fossils show a much wider range in the Pleistocene. Bones have turned up on Amchitka in the Aleutians, in Monterey Bay in California, and on Honshu in Japan. A rib from Kiska Island was dated to about 1,000 years old. Bones from St. Lawrence Island came from an animal that lived between 800 and 920 CE. Aleut accounts suggest that sea cows still lived in the Near Islands shortly before 1741.

GBIF holds records of the species from 4 countries, all of them specimens or fossils. The Commander Islands themselves had no people until 1825, when the Russian-American Company moved Aleuts there.

Diet and feeding

Steller's sea cow was a strict herbivore, and it ate mostly kelp. It fed on brown and red algae, with seagrass as a minor part of the diet. Because it floated, it could reach only plants within about 1 metre of the surface. It took only the soft parts of the kelp, so tough stems and holdfasts washed ashore in heaps. Canopy kelp holds fewer chemical deterrents than deeper kelp, which probably let the sea cow graze safely.

An animal spent most of the day feeding and lifted its head to breathe every 4 to 5 minutes. It pulled itself along the shallows with its hooked forelimbs while it grazed. The bristles on the lip tore seaweed stalks and held the food, and the horny plates chewed it. Its gut was about 151 metres long, more than 20 times the length of the body. In winter the kelp grew slowly, and the animals became so thin that their ribs showed.

Behaviour and social life

Steller described the sea cow as highly social. It lived in small family groups, and herds held males, females and young together. Adults kept the calves in the middle of the herd, or between themselves and the shore. When hunters harpooned a female, the others rammed and rocked the boat. Her mate followed the boat to shore and stayed near her body after she died.

Steller believed the species was monogamous, and the pair bond seemed strong. The animals showed almost no fear of people. Boats could row into a herd, and men could wade among the animals with little reaction. After feeding, the animals often slept on their backs at the surface. They swam slowly by sweeping the fluke from side to side, and faster with strong vertical beats.

The forelimbs anchored the body against the surf, and a male used them to hold his partner during mating. Steller wrote that the sea cow could not dive or even submerge completely. Domning doubted this claim, though he agreed that the animal spent most of its time afloat.

Communication and senses

Steller reported that the sea cow was nearly mute. Its only sounds were heavy breathing, a horse-like snort and a sigh. The eyes were small, sat halfway between the nostrils and the ears, and had black irises. A third eyelid covered each eye while the animal fed among the rocks. There were no eyelashes and no external ear flaps.

The nostrils were about 5 cm across and sat near the tip of the snout. Long bristles on the muzzle probably worked as feelers in murky water, as in living sirenians. Like other sirenians, the animal is thought to have relied on touch more than on sight.

Reproduction and life cycle

Mating took place in early spring. Steller judged that gestation lasted a little over a year. Calves could arrive at any time, but most births fell in early autumn. A female had one pair of mammary glands and bore a single calf at a time. Steller saw more calves in autumn than in any other season.

No record gives the lifespan of the species. Living sirenians average 50 to 70 years, with a maximum near 73, so the sea cow probably lived as long. Slow breeding, with one calf every few years, left the population unable to recover from hunting. Calves probably nursed for many months, as dugong calves do.

Predators and threats

Nobody knows whether the sea cow had a natural predator. Killer whales may have hunted it, though its buoyancy would have made it hard to drown. The rocky kelp forests it lived in may have kept sharks away. Adults guarded the calves, which suggests some real threat from predators.

Seabirds perched on the exposed backs of the animals and picked off a parasite, a whale louse named Cyamus rhytinae. Steller also found a roundworm inside the gut. The real threat was people. Sea otter hunting may have added to the pressure, because urchins spread when otters vanish and eat the kelp. Hunters speared an animal from the shallows and waited for the body to drift ashore, and many carcasses were lost.

Population and conservation

The IUCN lists Steller's sea cow as Extinct. Genetic work in 2021 showed that the Commander Islands animals were the last remnant of a population once spread across the North Pacific. Their genetic diversity was as low as that of the last woolly mammoths on Wrangel Island. A bottleneck about 400,000 years ago and shrinking habitat during the ice ages had already cut the numbers. By the time sea levels settled about 5,000 years ago, the population was already tiny.

When Europeans arrived, perhaps 2,000 animals remained. Stejneger estimated in 1887 that fewer than 1,500 had been alive at Steller's discovery. A hunting ban was ordered for the islands in 1755, but by then the animal was already rare. Ivan Korovin hunted sea cows in 1762, and Dimitri Bragin saw none in 1772. Brandt concluded that the species was extinct by 1768.

Native people of Attu told Lucien Turner that sea cows survived into the 1800s. In 1962 a whaling crew reported six large animals, 6 to 8 metres long, grazing off Kamchatka. None of these later sightings has been confirmed. Two groups now say they want to bring the species back by editing the dugong genome, but no suitable surrogate mother exists.

Relationship with humans

Steller's crew failed on their first attempt to catch one, because the hook could not pierce the hide. A month later a harpooner speared one, and men on shore hauled it in with a cable. After that the animals were easy to kill, and fur traders detoured to the islands to restock. The meat tasted like beef and was slow to spoil. The fat burned as odourless lamp oil, and the crew drank it by the cup. The milk was drunk or churned into butter, and the hide made shoes, belts and skin boats.

In the late 1800s the bones sold to museums at high prices. As of 2006, 27 nearly complete skeletons and 62 complete skulls were known, most assembled from several animals. Dense sea cow bone is still carved in Alaska as mermaid ivory, which the law allows because the species is extinct. Commander Island Aleuts played a game of accuracy called kakan with sea cow bones. The Pallas Picture of 1840 is the only known drawing thought to show a whole specimen.

In culture and myth

Writers return to the sea cow again and again. In Rudyard Kipling's story The White Seal, the seal Kotick asks Sea Cow for the way to a safe island. Scottish poet John Glenday wrote The Kelp Eaters in 2003, about the harpooning of the gentle animals. W. G. Sebald's Nach der Natur of 1995 and Andrei Bronnikov's Species Evanescens of 2009 both tell of its loss. The 2023 Finnish novel Beasts of the Sea by Iida Turpeinen follows a skeleton to a Helsinki museum.

In Russian hunting tradition, the animal was the cabbage-eater, a floating store of meat among the sea cabbage. In the tradition of naturalists, the gentle giant became a warning story of human greed, the first marine mammal that hunting erased. In cryptozoology, Loren Coleman suggested that the species reached Hudson Bay, to explain sea monster reports, with little evidence. Etienne de France's 2012 film Tales of a Sea Cow imagines the animal found alive off Greenland in 2006.