The Steller sea cow, Hydrodamalis gigas, was an extinct marine mammal described by German naturalist Georg Wilhelm Steller in 1741. Steller discovered the species when he was shipwrecked on Bering Island during Vitus Bering’s Great Northern Expedition. This encounter marked the beginning of its known, short period of existence. The observations made by Steller during his time on the island provide nearly all the detailed information available about this colossal creature.
Physical Characteristics and Home
The Steller sea cow was an immense aquatic mammal, considerably larger than any modern sirenian. Adults could reach lengths of 8 to 10 meters (26 to 33 feet) and weigh between 8 to 10 metric tons (17,600 to 22,000 pounds). Its physical appearance resembled a manatee or dugong.
This creature possessed thick, dark, brownish-black skin, sometimes with white patches, which was rough and wrinkled, leading to the nickname “bark animal.” Its head was small, featuring small eyes and ears.
Unlike other sirenians, the Steller sea cow had no teeth, instead using two horny plates in its mouth and dense bristles on its large upper lip to process food. Its forelimbs were stumpy flippers, used for steering, while its tail was forked, similar to a whale’s or dugong’s. The animal also had a thick layer of blubber, 8–10 cm (3–4 inches) thick, an adaptation to the cold waters of its environment, which made it positively buoyant and unable to fully submerge.
The Steller sea cow’s habitat was restricted to the shallow, coastal waters around the Commander Islands in the Bering Sea. Fossil evidence indicates its range was much wider during the Pleistocene epoch, extending across the North Pacific to areas like California and Japan, but it had significantly contracted due to glacial cycles. These shallow areas provided protection and a stable environment.
Diet and Temperament
The Steller sea cow was a herbivore, primarily consuming kelp and other seaweeds. It fed on canopy kelp, accessing food up to about 1 meter (3.3 feet) below the tide due to its positive buoyancy. Its large, prehensile upper lip, covered with stiff bristles, was adapted for tearing and gathering these marine plants.
This marine giant was known for its docile and slow-moving temperament. Steller noted that the sea cows showed little fear of humans, a trait that made them easy targets for hunters. They were social animals, often seen in groups, and Steller observed instances where other sea cows tried to assist an injured member or a mate followed a captured individual to shore.
Rapid Extinction and Modern Relevance
The Steller sea cow’s existence known to Europeans was brief, with its extinction occurring swiftly after its discovery. Described in 1741, the last known sighting of the species was around 1768. This rapid decline was almost entirely due to overhunting by humans.
Russian fur traders and explorers, en route to hunt sea otters in the North Pacific, found the Steller sea cow a convenient food source. They hunted the animals for their meat, fat for cooking and oil, and thick hides for clothing and boat construction. The sea cow’s large size, slow movement, and inability to submerge made it an easy target for hunters. Records indicate that hunting far exceeded sustainable limits, with an average of 123 individuals killed per year between 1743 and 1762, far surpassing the estimated sustainable catch of 17 per year.
The Steller sea cow’s extinction serves as an example of human impact on biodiversity and offers lessons for modern conservation efforts. Its fate highlights the vulnerability of isolated populations. The “sea cow effect” is a concept suggesting that the sea cow’s grazing habits of the kelp canopy allowed more sunlight to reach the understory, promoting biodiversity and strengthening kelp forest ecosystems. The absence of this megaherbivore may have contributed to the decline seen in some kelp forests today. The conservation of its closest living relatives, manatees and dugongs, which face threats, is now informed by the story of the Steller sea cow.