Hydrodamalis gigas

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Kingdom Animalia

Hunt on the Steller's sea cow. Unknown copyright licence.
Phylum Chordata 
Class Mammalia
Order Sirenia
Family Dugongidae
Genus Hydrodamalis
Species Hydrodamalis gigas
Authority (Zimmermann, 1780)
 
English Name Steller's Sea Cow
Danish Name Stellers Søko
Dutch Name Steller-zeekoe
French Name Rhytine de Steller
German Name Stellersche Seekuh, Riesenseekuh, Borkentier
Norwegian Name Stellers Sjøku
Polish Name Krowa Morska
Portuguese Name Dugongo de Steller
Spanish Name Vaca Marina de Steller
Swedish Name Stellers Sjöko
 
Synonyms Manati gigas Zimmermann 1780; Manati balaenurus Boddaert 1785; Trichechus manatus var. borealis Gmelin, 1788; Hydrodamalis stelleri Retzius 1794; Sirene borealis Link, 1794; Manatus borealis Link, 1795; Trichechus borealis Shaw, 1800; Rytina manatus borealis Illiger, 1811; Nepus stelleri G. Fischer, 1814; Rytina borealis Illiger, 1815; Rytina cetacea Illiger, 1815; Rytina stelleri Desmarest, 1819; Stellerus borealis Desmarest, 1822; Haligyna borealis Billberg, 1827; Rytina borealis F. Cuvier, 1836; Rhytine stelleri Burmeister, 1837; Rytina gigas Gray, 1850; Manatus gigas Lucas, 1891; Hydrodamalis gigas Palmer, 1895.
 
Taxonomy A cladistic analysis of the Sirenia (Domning, 1994) has shown that Hydrodamalis falls within the family Dugongidae. The genera Dusisiren and Hydrodamalis form the sub-family Hydrodamalinae. Domning (1976; 1978; 1994) has commented on the relatively good fossil record of the hydrodamalines and its documentation of the transition from a more traditional sirenian ancestor to the highly specialized Hydrodamalis. (Weinstein & Patton, 2000)
 
Characteristics Steller's Sea Cows were the largest and the only cold-water members of the scientific order 'Sirenia' to which manatees and dugongs also belong. These sea cows could reach a length of about 7,9 meters (25,9 feet). Published mass estimates range from 5400 to 11196 kilograms. With a heavy bone structure, they had huge midsections, a disproportionately small head, and a large, flat, twin-lobed tail. In the rough sea it was protected from rocks and ice floes by its 3-cm (1-inch) thick bark-like black skin (see left picture) and a 20-cm (4-9 inches) thick fat layer. Their external ear openings were only about the size of a pea, but the internal ear bones were very large, so excellent hearing can be assumed, although when they were feeding, would completely ignore even a boat. The Steller's sea cow was almost mute, making only deep breathing sounds when coming up for air and loud moaning sounds when wounded (Forsten & Youngman 1982).
 
Lifestyle The Steller's Sea Cow was gregarious, and herds appear to have included juveniles, males and females. Juveniles were kept toward the middle of the herd, and Steller (1751) describes herd members attempting to come to the aid of captured individuals. Steller's Sea Cows appears to have been monogamous, and Steller's account of the animal's behaviour suggests the pair bond was quite strong. Individuals spent the majority of their time feeding or resting, and Steller (1751) notes that the head could be kept submerged for 4-5 minutes at a time. Several first-hand observers comment on the apparent fearlessness of this large sea cow. According to Steller (1751), boats could be easily rowed into a herd and humans could wade among individuals near shore with little or no reaction. (Weinstein & Patton, 2000)
 
Range & Habitat They inhabited the shallow cold marine waters rich in algae and sea grass near the shore around Bering Island and Medney Island (Copper Island). These two islands are, together with two small islets, part of the Komandorski Islands (Commander Islands), a group of treeless islands east of the Kamchatka Peninsula in the Russian Far East, in the Bering Sea. (Forsten & Youngman 1982)

Image: range map of the Steller's sea cow. The red dot shows the position of the Komandorski Islands. Created by Peter Maas for The Extinction Website. This image has been released under the Creative Commons Attribution Non-commercial No Derivatives 3.0 Licence.

Fossil evidence indicates that the past distribution of the Steller's Sea Cow was much wider, including the coasts of Japan and North America. A fossil ancestor of the Steller's Sea Cow was the Dugong Sea Cow (Hydrodamalis cuestae). Fossil remains of this prehistoric sea cow are known from as far south as the southern coast of California. Steller (1751) notes that individuals or herds were often found near the mouths of stream or rivers, which suggests they could not tolerate drinking marine water. (Weinstein & Patton, 2000)

 
Food Steller's Sea Cows consumed sea algae lying near the surface, sea grasses, but primarily soft kelp. Since lacking teeth, it ground its food by its deeply grooved keratinous plates in the mandibles. Seasonal food availability may have been a problem for the Bering Sea population, as Steller described individuals losing enough weight during the winter months to cause their ribs and vertebrae to be visible under the skin. Steller notes that individuals or herds were often found near the mouths of freshwater streams or rivers, which suggests they could not tolerate drinking marine water.
 
Reproduction Few details are known of the mating system of the Steller's Sea Cow. Steller describes them, as monogamous and mating activities appear to have been concentrated in the early spring. Steller's account of the animal's behaviour suggests the pair bond was quite strong. Offspring were observed to be born at anytime of the year, but most births took place in early autumn. Females produced only one calf per breeding attempt. Steller inferred the length of gestation to be over one year.
 
History & Population

The ancestor to Steller's Sea Cow was possibly an extinct Dugongidae sea cow, Dusisiren jordani, previously named Metaxytherium jordani. Dusisiren was common in the shallow coastal waters of late Miocene California 10-12 million years ago. Although Sirenian evolution is not fully understood, there is a very clear and compelling fossil record leading up to Steller's sea cow (Domning 1987). 

Mitochondrial DNA research suggest that the sea cow-dugong divergence was likely as ancient as the dugong-manatee split (30 million years ago). The sea cow-dugong divergence appears to have been much earlier, namely 22 million years ago, than the previously estimated 4–8 million years ago. (Ozowa et al. 1997) Hydrodamalis cuestae had evolved by late Miocene time, around 5 million years ago (Dykens & Gillette 2006). This fossil species is considered to be ancestral to the Steller's sea cow (Deméré 2006).

The crew of Vitus Bering's ship 'St. Peter, shipwrecked off the coast of Kamchatka in early November 1741. One of them was Georg Wilhelm Steller, the naturalist and physician on Bering's expedition. During the months that Steller and the other survivors of Bering's crew spent on what would later be named Bering Island. They discovered there the Steller's sea cow, Hydrodamalis gigas. The presence of Steller's sea cow off Bering Island was only as an evolutionary relict, a small population confined to a very restricted area of cold waters near the Kamchatkan peninsula (Dykens & Gillette 2006). Steller was able to gather considerable information on the habits of the Stelller's Sea Cow as well as an extensive set of measurements of various parts of the sea cow's anatomy. Bering's crew could escape in August 1742, after building a new boat from the wreckage of the 'St. Peter'. Steller published his observations in 1751. Another extinct species, which was discovered by Georg Wilhelm Steller at Bering Island, was the Spectacled Cormorant (Phalacrocorax perspicillatus).

The meat of these sea cows, which most often referred to as being similar to veal and remained fresh for much longer than any other available meat source in that time. The fat was described as tasting like sweet almond-oil. Bering's crew only killed their first Steller's Sea Cow 6 weeks before their escape in August 1742. The meat was crucial in restoring their strength during the final stages of building their new boat. Based on the information from Steller's observations, the crew of other ships arriving there unscrupulously slaughtered the sea cows for their meat and fat. Also fur hunters flocked to the area. Only one out of five Steller's Sea Cows hit by harpoon or rifle fire was retrieved, but the majority escaped only to die at sea from their injuries. 

Off Copper Island, where the population was initially low, there were no animals left by 1754 . In 1768, explorer Martin Sauer entered in his journal an account of the death of the last known Steller's Sea Cow off Bering Island. So only 27 years after Steller first saw these sea cows, the Steller's Sea Cow became extinct. (Forsten & Youngman 1982)

 
Extinction Causes The Steller’s Sea Cow was hunted primarily as a source of food. Steller (1751) describes the meat as being easily prepared and similar to beef in taste and texture. The blubber was useful for cooking and was also a source of lamp oil. The milk of harvested cows was consumed directly or made into butter. The thick, tough hide was used for shoes, belts and to make skin-covered boats. No sustained yield practices were used, and the low reproductive rate of the population, combined with its probable existence in a sub-optimal environment likely hastened the species' decline. Anderson (1995) has also noted that the intense hunting of sea otters on the Bering Sea islands may have contributed to the final extinction of the Steller's Sea Cow. It is known that sea urchin populations can severely deplete sea grass and algae communities when otters are removed, and as this happened on the Bering Sea islands, the sea cows would have faced a new competitor for food.  (Weinstein & Patton, 2000)
 
Conservation Attempts Yakolev, a first-hand observer of the Steller's Sea Cow, claims that an order was given to the headquarters of the outpost on the Komandorskiye Islands on 27 November 1755, prohibiting hunting of the sea cows (translated in Domning, 1978).
 
Museum Specimens Photo: a reconstructed skull of the Steller's sea cow in the Rosensteinmuseum in Stuttgart, Germany. Courtesy by Sordes. Copyright, all rights reserved.

Today, the sea cow seems an almost imaginary creature, but Steller's descriptions and a few intact skeletons, skulls and pieces of skin, preserved in museums, prove that this amazing animal lived in the Bering Sea just over 200 years ago. 

Specimens can be found in the Royal Museum (Edinburgh, United Kingdom), Natural History Museum (London, United Kingdom), The Manchester Museum (Manchester, United Kingdom), Naturkundemuseum (Braunschweig, Germany), Schausammlung (Darmstadt, Germany), Staatliches Museum für Tierkunde (Dresden, Germany), Roemer- und Pelizaeus-Museum (Hildesheim, Germany), Niedersächsisches Landesmuseum (Hanover, Germany), Naturhistoriska Museum (Götenborg, Sweden), Zoologiska museet (Lund, Sweden), Naturhistoriska Riksmuseum (Stockholm, Sweden), Museum of Natural History (Helsinki, Finland), Muséum National d'Histoire Naturelle (Lyon, France), Musée National d'Histoire Naturelle (Paris, France), Naturhistorisches Museum (Vienna, Austria), Museum of Zoology (Krakow, Poland), Hungarian Natural History Museum (Budapest, Hungary), Oceanographic Museum (Monaco-Ville, Monaco), Naturkundemuseum (Basle, Switzerland), Nature Museum (Kharkiv, Ukraine), Museum of Paleontology (Kiev, Ukraine), Museum of Zoology (Kiev, Ukraine), Zoological Museum (Lviv, Ukraine), Zoological Museum (Odessa, Ukraine), Museum Ekaterinburg (Ekaterinburg, Russian Federation), Museum Of Regional Studies (Irkutsk, Russian Federation), Regional Lore Museum (Khabarovsk, Russian Federation), Zoological Museum (Moscow, Russian Federation), Paleontological Institute (Moscow, Russian Federation), Biological Timiryazev Museum (Moscow, Russian Federation), State Darwin Museum (Moscow, Russian Federation), Museum of Local Lore (Nikolskoye, Bering Island, Russian Federation), Museum of Kamchatka Local Lore (Petropawlowsk, Kamchatka, Russian Federation), Zoological Institute of Academy of Sciences (St. Petersburg, Russian Federation), Oceanarium (Wladiwostok, Russian Federation), Primorsky Museum of Local Lore (Wladiwostok, Russian Federation), Zoological Museum of the Far Eastern State University (Wladiwostok, Russian Federation), Numata Fossil Laboratory (Numata-cho, Hokkaido, Japan), Redpath Museum (Montreal, Quebec, Canada), National Museum of Natural Sciences (Ottawa, Canada), Australian Museum (Sydney, Australia), Smithsonian's National Museum of Natural History (Washington DC, USA), Burke Museum of Natural History and Culture (Seattle, Washington, USA), Museum of Comparative Zoology (Cambridge, Massachusets, USA), Museum of Paleontology (Berkeley, California, USA), Museum of Vertebrate Zoology (Berkeley, California, USA)

 
Relatives The closest living relatives of the Steller's sea cow is the dugong (Dugong dugon) followed by the three manatee species; the West Indian manatee (Trichechus manatus), the African manatee (Trichechus senegalensis), and the Amazonian manatee (Trichechus inunguis). Other living relatives are the Hyrax species; the Southern tree hyrax (Dendrohyrax arboreus), the Western tree hyrax (Dendrohyrax dorsalis), the yellow-spotted rock hyrax (Heterohyrax bruceii), and the Cape hyrax (Procavia capensis). More distant relatives are the three elephant species; the Asian elephant (Elephas maximus), the African Savannah Elephant (Loxodonta africana), and the African Forest Elephant (Loxodonta cyclotis). (Ozowa et al. 1997)

Image: a  maximum parsimony tree showing the relatedness of the superorder of Paenungulata, consisting of the orders of Proboscidae (elephants), Sirenia (sea cows and manatees) and Hyracoidea (hyraxes). Based on Ozowa et al. Created by Peter Maas for The Extinction Website. This image has been released under the Creative Commons Attribution Non-commercial No Derivatives 3.0 Licence.

Sadly, some of the closest relatives of the Steller's sea cow, like the dugong (Dugong dugon), are endangered today. These species' populations are declining as a result of pollution, deaths caused by the propellers of outboard boat motors, and habitat loss caused by human development.

 
Links

IUCN Red List of Threatened Species – Hydrodamalis gigas.  

Stellers Seacow by Hans Rothauscher.

University of Michigan – Animal Diversity Web – Hydrodamalis gigas – Steller’s Sea Cow.

Steller’s Sea Cow – Kevin R.’s Report.

Sirenian International – Steller’s seacow.

Extinct Stock Photography.

Istitut Virtuel de Cryptozoologie – La rhytine de steller a-t-elle vraiment disparu?

Steller tengeri tehene – Hydrodamalis gigas (Steller, 1751).

Hydrodamalis gigas - Stellerzeekoe.

 
References Anderson, P. 1995. Competition, predation, and the evolution and extinction of Steller’s sea cow, Hydrodamalis gigas. Marine Mammal Science, 11: 391-394.

Deméré, T. 2006. SDNHM: Fossil Sea Cow (Dugong) Discovered. San Diego Natural History Museum. Downloaded on 12 August 2006 from http://www.sdnhm.org/research/paleontology/seacow.html. 

Domning, D., V. de Buffrénil. 1991. Hydrostasis in the Sirenia: quantitative data and functional interpretations. Marine Mammal Science, 7: 331-368

Domning, D. 1976. An ecological model for Late Tertiary sirenian evolution in the North Pacific Ocean. Systematic Zoology, 25: 352-362

Domning, D. 1978. Sirenian evolution in the North Pacific Ocean. University of California Publications in Geological Sciences, 118: 1-176

Domning, D. P. 1987. Sea cow family reunion. Natural History April 1987 Vol.96(4):64-71.

Domning, D. 1994. A phylogenetic analysis of the Sirenia. Proceedings of the San Diego Society of Natural History, 29: 177-189

Domning, D. 1996. Bibliography and index of the Sirenia and Desmostylia. Smithsonian Contributions to Paleobiology., 80: 1-611. 

Dykens, M. & Gillette, L. 2006. SDNHM Fossil Mysteries Field Guide: Extinct Sea Cow. San Diego Natural History Museum. Downloaded on 12 August 2006 from http://www.sdnhm.org/exhibits/mystery/fg_seacow.html. 

Forsten, A. & Youngman, P.M. 1982. Hydrodamalis gigas. Mammalian Species, 165: 1-3. American Society of Mammalogists. (Available online)

Ozowa T., Hayashi S. and Mikhelson V.M. 1997. Phylogenetic position of mammoth and Steller’s sea cow within Tethyteria demonstrated by mitochondrial DNA sequences. J. Molecular Evolution 44: 406-413.

Rothauscher, H. 2005. Steller's Seacow. Accessed November 13th, 2005 at http://www.hans-rothauscher.de/steller/steller.htm 

Steller, G. 1899 (orig. 1751). The beasts of the sea. (translated by W. Miller and J. E. Miller, orig. published in 1751).. Pp. 180-201 in D. Jordan, ed. The fur seals and fur seal islands of the North Pacific Ocean. Part 3.. Washington, D.C.: U.S. Government Printing Office

Weinstein, B. and J. Patton. 2000. "Hydrodamalis gigas" (On-line), Animal Diversity Web. Accessed November 06, 2005 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hydrodamalis_gigas.html 

World Conservation Monitoring Centre 1996. Hydrodamalis gigas. In: IUCN 2004. 2004 IUCN Red List of Threatened Species. <www.redlist.org>. Downloaded on 06 November 2005.

Last updated: 12th August 2006.

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