Steller’s sea cow – the giant sea cow of the North Pacific

The Steller's sea cow (Hydrodamalis gigas) is a herbivorous marine mammal and the largest sea cow species, measuring a length of up to 8 m and having a weight of more than 4 tons. It is – excluding the great whales – the largest marine mammal that existed in historic times. Its nearest relative is the dugong (Dugong dugong) of the tropical Indopacific. But also the 3 species of manatees (Trichechus ssp.) at the tropical Atlantic coasts and in the river deltas on both sides of the warm Atlantic belong to the sea cow group. But they form a different family (Manatidae). The main difference between manatees and dugongs is the shape of the tail. Manatees have rounded tails, while the dugongs have fluked and dolphin-like tails. The tail of the gigantic Steller’s sea cow was almost 2 m broad. Another difference is that the skull and teeth of the dugongs are different to those of the manatees. Whilst all the existing sea cow species prefer warm water, the Steller’s sea cow lived in the cold Northern Pacific. Even fossils indicate that the species was formerly widespread along the North Pacific coast, reaching as far south to Japan and to California in the US. They were really abundant throughout the whole Northern Pacific.

Natural history illustration of Steller’s sea cow ①(Click to view larger image).

When the species was first described by Georg Wilhelm Steller in 1741, its range had been already limited to a single, isolated population surrounding the uninhabited Commander Islands. Steller was stranded with the Behring expedition on these islands and had enough time to give a detailed description of the animals and their behavior.According to him the animal looked somewhat like a large seal, but had two stout forelimbs and a whale-like fluke. The sea cow uses the fore limbs for swimming, for walking on the shallow parts of the shore, for supporting herself on the rocks, for digging for algae and sea grass and of course also as defense mechanism. Steller reports that the animal is covered with a thick hide, more like the bark of an old oak than an animal skin. Therefore this sea cow was also called “Bark animal”. The hide is black, mangy, wrinkled, rough, hard and tough. It is void of hairs.

Different sea cows in the wold and their habitat(Click to view larger image).

Today we know that the wrinkles and tubes of the skin were caused by parasites, the amphipod Cyamus rhytinae, and also by some cirripedes, which drilled their pipes through the whole skin. Below the skin there was a 10cm thick layer of fat. The 7cm thick epidermis was very elastic. This skin structure protected the animal against mechanical injuries caused by floating sheets of ice and also, when the animals were thrown by the waves against the rocky coast.

Size comparison of dugong, human and Steller’s sea cow(Click to view larger image).

Compared to the huge sea cow’s body, its head is small and short. The upper lip is very large and broad and extends beyond the mandible. The mouth thus appears to be located underneath the skull. The mouth itself is rather small, toothless, and equipped with double lips, both above and below. When the sea cow closes the mouth, the space between the lips is filled up with a dense array of very thick, white and 38 mm long bristles. These bristles replace the teeth and are used to pull out seaweed and hold food. Mastication is performed by two white bones or solid tooth masses.

Skeleton of Steller’s sea cow(Click to view larger image).

The species was quickly wiped out by the sailors, seal hunters and fur traders who followed Bering's route to pass the islands to Alaska. They hunted the Steller’s sea cows both for food and for their hides, which were used to make boats. The sea cow was also hunted for its valuable subcutaneous fat, which was not only used for food, but also for oil lamps because it did not release any smoke or odour and could be kept for a long time in warm weather without becoming moldy. In 1768, only 27 years after its discovery, the slow-moving and easily captured Steller's sea cow was already hunted to extinction.

Today skulls and parts of the skeletons of the Steller’s sea cow can be seen quite often in the Natural History Museums and in Japan also in the Okinawa Churaumi Aquarium. Nevertheless a perfect whole skeleton is seldom to see. Probably there are only 10-20 perfect skeletons in the scientific collections worldwide. Most of them are in Russia and a few in Britain, France and Germany. - Therefore it is recommended to visit our Lost Zoo, because only here you can find and see this impressive Steller’s sea cow Not only in its full length but even alive.

Executive Curator
JURGEN LANGE