Steller's sea cow
|Steller's sea cow|
|Drawing by Steller in 1743 on a dead female, thought to be the only first-hand illustration|
The Steller's sea cow (Hydrodamalis gigas) is an extinct herbivorous marine mammal. It was the largest member of the order Sirenia, which includes its closest living relative, the dugong (Dugong dugon), and the manatees (Trichechus spp.). It reached up to 9 metres (30 ft) in length, making it among the largest mammals other than whales to have existed in the holocene epoch. It was first described by Georg Wilhelm Steller. Although the sea cow had formerly been abundant throughout the North Pacific, by the mid 1700s, its range had been limited to a single, isolated population surrounding the uninhabited Commander Islands. It was hunted for its meat, skin, and fat by fur traders, and was also hunted by aboriginals of the North Pacific coast. Within 27 years of discovery by Europeans, the slow-moving and easily captured Steller's sea cow was hunted to extinction.
Discovery and extinction
Steller's sea cow was discovered in the mid-18th century by Georg Wilhelm Steller, who studied a relict population near Bering Island while he was shipwrecked there. His account was written in his posthumous publication De bestiis marinis, or "The Beasts of the Sea". Their range at the time of their discovery was apparently restricted to the Commander Islands, though fossils discovered dating to the late Pleistocene were found in Monterey Bay, California. There is evidence that sea cows also inhabited the Near Islands during historic times. Although Steller had said they were numerous and found in herds, zoologist Leonhard Hess Stejneger later estimated that at discovery there had been fewer than 1,500 remaining, and thus had been in immediate danger of extinction from overhunting.
The species was quickly wiped out by the sailors, seal hunters, and fur traders who followed Vitus Bering's route past the islands to Alaska, who hunted it for its meat before sailing to nearby islands in search of sea otter pelts. It was also hunted for its valuable subcutaneous fat, which was not only used for food (usually as a butter substitute), but also for oil lamps because it did not give off any smoke or odor and could be kept for a long time in warm weather without spoiling. By 1768, 27 years after it had been discovered by Europeans, Steller's sea cow was extinct.
It has been argued that the sea cow's decline may have also been an indirect response to the harvest of sea otters by aboriginal people from the inland areas. With the otters reduced, the population of sea urchins would have increased and reduced availability of kelp, the sea cow's primary source of food. Thus, aboriginal hunting of both species may have contributed to the sea cow's disappearance from continental shorelines. In historic times, though, aboriginal hunting had depleted sea otter populations only in localized areas. The sea cow would have been easy prey for aboriginal hunters, who would likely have exterminated accessible populations with or without simultaneous otter hunting. In any event, the sea cow was limited to coastal areas off islands without a human population by the time Bering arrived, and was already endangered. It is possible that the extinction of these remaining endangered populations of sea cow could have been affected solely by the hunting of the sea cow for meat by fur-trading mariners of the time, and no other factors (such as overpopulation of sea urchins) need contributed.
The sea cow grew to at least 26 to 30 ft (8 to 9 m) in length as an adult, much larger than the manatee or dugong; however, concerning their weight, Steller's work contains two contradictory estimates: 4.4 and 26.8 short tons (4 and 24.3 metric tons). The true value is estimated to lie between these figures, at around 9 to 11 short tons (8 to 10 metric tons). Their large size was probably to reduce their surface-area-to-volume ratio and conserve heat. The forelimbs, according to Steller, were used as sort of a holdfast to anchor themselves down to prevent being swept away by the strong nearshore waves. Unlike other sirenians, the Steller's sea cow was positively buoyant, meaning they could not completely submerge. They had a thick epidermis to prevent injury from abrasions on sharp rocks and ice, and possibly to prevent the skin that is not submerged from drying out.
Its head was small and short compared to the huge body. The upper lip was large and broad, and extended so far beyond the mandible, that the mouth appeared to be located underneath the skull. Instead of teeth, Steller's sea cow had a dense array of white bristles, 1.5 inches (3.8 cm) long, which were used to pull out seaweed and hold food, and used keratinous plates for chewing. According to Steller, these plates, or "masticatory bones", were held together by papillae and had many small holes for nerves and arteries. The rostrum was pointed downwards, as in all sirenians, to better grasp kelp.
Like other sirenians, the Steller's sea cow was an obligate herbivore, and kelp was most likely their main food source. They may have also fed on seagrasses, but they could not have been a main food source while supporting a viable population, because they did not occur in sufficient numbers. Since they floated, they most likely fed on canopy kelp. Kelp releases a chemical deterrent to prevent grazing, but canopy kelp release a lower concentration, allowing the sea cows to graze without developing resistance.
Whether or not Stellar's sea cows had any predators is unknown. They may have been hunted by killer whales and sharks, but their buoyancy may have made it difficult for killer whales to drown them, and the rocky kelp forests may have protected them from sharks. According to Steller, the young were kept into positions wherein the adults would guard them from predators.
Portrayals in media
Tales of a Sea Cow is a 2012 film by Icelandic-French artist Etienne de France "documenting" a fictional 2006 re-discovery by scientists of a population of Steller's sea cows off the coast of Greenland via sound recordings or their calls. This film has been exhibited in public institutions such as art museums and universities in Europe. Art critic Annick Bureaud found the film a "tongue in cheek and joyous but unsettling fable".
- List of extinct animals
- List of extinct animals of North America
- List of recently extinct mammals
- Evolution of sirenians
- Holocene extinction
- Domning, D.; Anderson, P.K.; Turvey, S. (2008). Hydrodamalis gigas. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 19 August 2016.
- Steller, Georg W. (2011) . "The Manatee". In Royster, Paul. De Bestiis Marinis. Lincoln: University of Nebraska. pp. 13–43. ISBN 978-1-295-08525-5.
- Anderson, Paul K. (July 1995). "Competition, Predation, and the Evolution and Extinction of Steller's Sea Cow, Hydrodamalis gigas". Marine Mammal Science. Society for Marine Mammalogy. 11 (3): 391–394. doi:10.1111/j.1748-7692.1995.tb00294.x.
- MacDonald, Stephen O.; Cook, Joseph A. (2009). Recent Mammals of Alaska. University of Alaska Press. pp. 57–58. ISBN 978-1-60223-047-7.
- Corbett, D. G.; Causey, D.; Clemente, M.; Koch, P. L.; Doroff, A.; Lefavre, C.; West, D. (2008). "Aleut Hunters, Sea Otters, and Sea Cows". Human Impacts on Ancient Marine Ecosystems. University of California Press. pp. 43–76. ISBN 978-0-520-93429-0. JSTOR 10.1525/j.ctt1pphh3.
- Haycox, Stephen W. (2002). Alaska: An American Colony. Seattle: University of Washington Press. pp. 55, 144. ISBN 978-0-295-98249-6.
- Jones, Ryan T. (September 2011). "A 'Havock Made among Them': Animals, Empire, and Extinction in the Russian North Pacific, 1741–1810". Environmental History. 16 (4): 585–609. doi:10.1093/envhis/emr091. JSTOR 23049853.
- Estes, James A.; Burdin, Alexander; Doak, Daniel F. (2016). "Sea otters, kelp forests, and the extinction of Steller's sea cow". Proceedings of the National Academy of Sciences of the United States of America. 113 (4): 880–885. doi:10.1073/pnas.1502552112. PMC .
- Ellis, Richard (2004). No Turning Back: The Life and Death of Animal Species. New York City: Harper Perennial. p. 134. ISBN 978-0-06-055804-8.
- Turvey, ST; Risley, CL (March 22, 2006). "Modelling the extinction of Steller's sea cow". Biol Lett. 2 (1): 94–7. doi:10.1098/rsbl.2005.0415. PMC . PMID 17148336.
- Marsh, Helene; O'Shea, Thomas J.; Reynolds III, John E. (2011). "Steller's sea cow: discovery, biology and exploitation of a relict giant sirenian". Ecology and Conservation of the Sirenia: Dugongs and Manatees. New York: Cambridge University Press. pp. 18–35. ISBN 978-0-521-88828-8.
- Scheffer, Victor B. (November 1972). "The Weight of the Steller Sea Cow". Journal of Mammalogy. 53 (4): 912–914. doi:10.2307/1379236. JSTOR 1379236.
- Perrin, William F.; Wursig, Bernd; Thewissen, J. G. M. (2008). Encyclopedia of Marine Mammals (2 ed.). San Diego: Academic Press. p. 306. ISBN 978-0-12-373553-9.
- Whitmore, Jr., Frank C.; Gard, Jr., L. M. (1977). "Steller's Sea Cow (Hydrodamalis gigas) of Late Pleistocene Age from Amchitka, Aleutian Islands, Alaska" (PDF). Geological Survey Professional Paper. Washington D. C.: United States Government Printing Office. 1036: 9.
- "Tales of a Sea Cow (2012)". IMDb.
- "Etienne de France, "Tales of a Sea Cow" — Exhibition at Parco Arte Vivente, Torino, Italy". alan-shapiro.com.
- Bureaud, Annick. "Tales of a Sea Cow: A Fabulatory Science Story" (PDF). Retrieved August 19, 2016.
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