Animal Diversity Web

Ge­o­graphic Range

North Pa­cific Ocean: The range of Hy­dro­damalis gigas in his­toric times ap­pears to have been lim­ited to the coastal wa­ters of the Ko­man­dorskiye and Blizh­nie Is­lands in the Bering Sea. Ac­counts of sight­ings from other is­lands in the Bering Sea, along the north­west coast of North Amer­ica and the north­east coast of Asia, in the Arc­tic Ocean and Green­land are dif­fi­cult or im­pos­si­ble to con­firm and gen­er­ally dis­counted. Fos­sil ev­i­dence in­di­cates that the past dis­tri­b­u­tion of genus Hy­dro­damalis was much wider, in­clud­ing the coasts of Japan and North Amer­ica. Fos­sil re­mains of Hy­dro­damalis cues­tae are known from as far south as the south­ern coast of Cal­i­for­nia.

• Biogeographic Regions
• arctic ocean
  • native
• pacific ocean
  • native

Habi­tat

Hy­dro­damalis is known to have oc­curred in cold, shal­low, coastal ma­rine wa­ters rich in algae and sea grass. Herds were fre­quently found near the mouths of streams or rivers. Its range was re­stricted to is­lands in the Bering Sea dur­ing his­toric times, but ex­tended to Cal­i­for­nia and Japan dur­ing pre­his­toric times.

• Habitat Regions
• temperate
• polar
• saltwater or marine

• Aquatic Biomes
• coastal

• Other Habitat Features
• intertidal or littoral

Phys­i­cal De­scrip­tion

The few first-hand ac­counts of Hy­dro­damalis that are avail­able note sev­eral dis­tinc­tive fea­tures. The an­i­mal was con­sid­er­ably larger than any other ex­tant siren­ian. Steller (1751) gives a length of 296 inches (7.5 me­ters) for a fe­male spec­i­men that he ex­am­ined. Larger sizes have been sug­gested, but after ex­am­i­na­tion of avail­able skele­tal ma­te­r­ial Domn­ing (1978) es­ti­mated an upper size limit of about 7.9 me­ters. How­ever, Domn­ing (1978) also notes that the Bering Sea pop­u­la­tion ap­pears to have oc­cu­pied a sub-op­ti­mal habi­tat for the species that may have pre­vented in­di­vid­u­als from reach­ing their max­i­mum pos­si­ble size. Pub­lished mass es­ti­mates range from 5400 to 11,196 kilo­grams. It has been re­ported that Hy­dro­damalis dis­played sex­ual size di­mor­phism, but Domn­ing (1978) could find no ev­i­dence to sup­port this as­ser­tion.

Steller (1751) de­scribes the head and neck as being short and weakly de­lim­ited from the rest of the body. Pin­nae were ab­sent, the nos­trils were paired and lo­cated near the tip of the snout, and the eyes were rel­a­tively small. Many large, vib­ris­sae-like bris­tles sur­rounded the mouth. Teeth were ab­sent in adults, but the ker­ati­nous ros­tral pads found in other sire­ni­ans were re­tained in Hy­dro­damalis. The neck ap­pears to have been more flex­i­ble than in other liv­ing sire­ni­ans and may have helped the an­i­mal feed over a wider area with less move­ment of the large body. The body ta­pered cra­nially and cau­dally, but the belly and sides were rounded and swollen look­ing. When healthy, the back was slightly con­vex. Hy­dro­damalis re­sem­bled other dugongids in hav­ing a whale-like fluke at the end of its tail. The skin of the an­i­mal was un­usual in hav­ing a black, thick­ened, bark-like epi­der­mal layer that may have pro­tected it from abra­sion against rocks in the shal­lows where it fed.

The fore­limbs of Hy­dro­damalis are highly de­rived rel­a­tive to the flip­per-like limbs of most other sire­ni­ans. They lack pha­langes and show sev­eral spe­cial­iza­tions for a dis­tinc­tive style of lo­co­mo­tion. Steller (1751) de­scribed the fore­limbs as being rel­a­tively short with a dis­tinct hook-like shape. Sev­eral re­cent artis­tic re­con­struc­tions por­tray Hy­dro­damalis as hav­ing flip­per-like limbs, but draw­ings made by ob­servers who had seen live in­di­vid­u­als sup­port Steller's (1751) ac­count. The epi­der­mal layer was very thick on the limbs, and Steller (1751) de­scribes Hy­dro­damalis using the limbs to pull it­self along while feed­ing in shal­low water.

Domn­ing (1978) ex­am­ined the skele­tal struc­ture of the fore­limbs and pec­toral gir­dle of Hy­dro­damalis. Al­most all of the bones show ex­ten­sive mod­i­fi­ca­tion and changes in mus­cle orig­i­na­tions and in­ser­tions that re­flect a greater em­pha­sis on parasagit­tal move­ments of the limb. Domn­ing com­pares these spe­cial­iza­tions to those of gravipor­tal mam­mals and tree sloths, an­i­mals that also have rel­a­tively straight limbs that move in a parasagit­tal plane. Hy­dro­damalis ap­pears to have had a nar­rower, deeper chest in the area of the pec­toral gir­dle than most other sire­ni­ans, bring­ing the limbs closer to the mid­line of the body and al­low­ing greater fore-aft mo­bil­ity of the limbs. This re­con­struc­tion strongly sug­gests that Hy­dro­damalis was spe­cial­ized to "walk" along in the shal­lows while feed­ing, as de­scribed by Steller (1751).

Steller (1751) and other first-hand ob­servers also de­scribe Hy­dro­damalis as being un­able to dive or even com­pletely sub­merge its body. Sire­ni­ans gen­er­ally have pre­cise con­trol of their buoy­ancy as a re­sult of spe­cial­iza­tions of their skele­ton, di­aphragm and lungs (Domn­ing and de Buffrénil, 1991). Domn­ing (1978) spec­u­lated that in­creased buoy­ancy may have been in­di­rectly se­lected for as a con­se­quence of large body size be­cause of cor­re­spond­ing in­creases in lung vol­ume, in­testi­nal vol­ume and thick­ness of blub­ber. There may also have been a di­rect se­lec­tive ad­van­tage to in­creased buoy­ancy be­cause it would have re­duced the area ac­ces­si­ble to par­a­sites, re­duced drag when swim­ming, re­duced heat loss to the water via con­duc­tion, and al­lowed Hy­dro­damalis to enter shal­lower wa­ters to feed and es­cape preda­tors. How­ever, Domn­ing (1978) dis­putes Steller's (1751) claim that Hy­dro­damalis could not dive, even if it spent most of its time float­ing. (Domn­ing and de Buffrénil, 1991; Domn­ing, 1978; Steller, 1899 (orig. 1751))

• Other Physical Features
• endothermic
• bilateral symmetry

• Range mass

  5400 to 11196 kg

  11894.27 to 24660.79 lb

• Average mass

  8000 kg

  17621.15 lb

Re­pro­duc­tion

Few de­tails are known of the mat­ing sys­tem of Hy­dro­damalis. Steller (1751) de­scribes them as monog­a­mous, and mat­ing ac­tiv­i­ties ap­pear to have been con­cen­trated in the early spring. Off­spring were ob­served to be born at any­time of year, but most births took place in early au­tumn. Fe­males pro­duced only one calf per breed­ing at­tempt. Steller (1751) in­ferred the length of ges­ta­tion to be over one year. (Steller, 1899 (orig. 1751))

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• viviparous

Be­hav­ior

Hy­dro­damalis 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. As noted above, Hy­dro­damalis ap­pears to have been monog­a­mous, and Steller's ac­count of the an­i­mal's be­hav­ior sug­gests the pair bond was quite strong.

Herds of Hy­dro­damalis con­gre­gated in shal­low wa­ters near the shore, some­times so close that hunters could sim­ply wade out to them. 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. 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 Hy­dro­damalis. 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.

• Key Behaviors
• motile

Com­mu­ni­ca­tion and Per­cep­tion

• Perception Channels
• tactile
• chemical

Food Habits

First-hand ac­counts of the feed­ing habits of Hy­dro­damalis are often vague and con­tra­dic­tory. Based on Steller's (1751) de­scrip­tions of plants he saw Hy­dro­damalis eat­ing, it ap­pears that brown and red algae were its pri­mary food sources, with sea grass a minor com­po­nent of the diet (Domn­ing, 1976; 1978; An­der­son, 1995). Liv­ing sire­ni­ans are known to in­gest brown algae in times of food short­age, but this does not ap­pear to be a pre­ferred food. Steller (1751) de­scribes Hy­dro­damalis as feed­ing on parts of algae and sea grass grow­ing near the sur­face or on rocks in the shal­lows. Sea­sonal food avail­abil­ity may have been a prob­lem for the Bering Sea pop­u­la­tion, as Steller (1751) de­scribes in­di­vid­u­als los­ing enough weight dur­ing the win­ter months to cause their ribs and ver­te­brae to be vis­i­ble under the skin.

Many fea­tures of the feed­ing sys­tem of Hy­dro­damalis in­di­cate that it had adapted to its un­usual diet of soft kelps and algae. Per­haps the most ob­vi­ous mod­i­fi­ca­tion is the ab­sence of teeth. Hy­dro­damalis re­tained the ker­ati­nous ros­tral pads found in other sea cows, and the pres­ence of in­ter­lock­ing ridges and grooves on these pads as well as re­in­force­ment of the ros­trum may be ev­i­dence that the an­i­mal used these pads to mas­ti­cate its food. There is also skele­tal and my­olog­i­cal ev­i­dence that sug­gests the crop­ping and mash­ing mo­tions of the front of the mouth were em­pha­sized at the ex­pense of more tra­di­tional chew­ing move­ments in Hy­dro­damalis. In his ac­count, Steller (1751) also de­scribes the an­i­mal as mas­ti­cat­ing its food with the ker­ati­nous plates. Liv­ing dugongids finely chew sea grasses, but tend to swal­low in­gested algae rel­a­tively in­tact. Based on this ob­ser­va­tion, Domn­ing (1978) hy­poth­e­sized that Hy­dro­damalis may have sim­ply ripped off pieces of kelp and swal­lowed them with lit­tle or no pro­cess­ing in the mouth. The great en­large­ment of the gut re­ported by Steller (1751) prob­a­bly re­flects the need for more thor­ough chem­i­cal di­ges­tion of food due to the lack of thor­ough mas­ti­ca­tion. The amount of ros­tral de­flec­tion seen in Hy­dro­damalis is con­sis­tent with an em­pha­sis on sur­face feed­ing habits, and the highly mo­bile lips were used in gath­er­ing and crop­ping food, as in other ex­tant sea cows. The claw-like fore­limbs may also have been used to dis­lodge plant mat­ter from rocks.

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Hy­dro­damalis 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.

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Hy­dro­damalis had no neg­a­tive eco­nomic ef­fects on hu­mans.

Con­ser­va­tion Sta­tus

It is not known ex­actly when the last in­di­vid­ual of Hy­dro­damalis died, but it ap­pears likely that the species was ex­tinct by 1768. Yakolev, a first-hand ob­server of Hy­dro­damalis, claims that an order was given to the head­quar­ters of the out­post on the Ko­man­dorskiye Is­lands on No­vem­ber 27, 1755, pro­hibit­ing hunt­ing of the sea cows (trans­lated in Domn­ing, 1978). How­ever, he also notes that by this time Hy­dro­damalis was ex­tremely rare.

Much has been writ­ten about the ex­tinc­tion of Hy­dro­damalis at the hands of hu­mans. The hunt­ing prac­tices de­scribed in first-hand ac­counts are ex­tremely waste­ful. Often, hunters would sim­ply wade out to an in­di­vid­ual, spear it, and then allow the an­i­mal to swim off, hop­ing that it would later die and drift to shore. 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 Hy­dro­damalis. 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. A sim­i­lar course of events may have oc­curred 12,000-14,000 years ear­lier along the coast of Asia and North Amer­ica as abo­rig­i­nal peo­ples col­o­nized the areas and began hunt­ing ot­ters and sea cows (An­der­son, 1995).

• IUCN Red List

  Extinct
  More information

• IUCN Red List

  Extinct
  More information

Other Com­ments

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.

Steller (1751) de­scribes par­a­sitic crus­taceans that some­times se­verely in­fested the sub­merged areas of Hy­dro­damalis. There has been much spec­u­la­tion as to the iden­tity and re­la­tion­ships of these par­a­sites, but the lack of pre­served spec­i­mens has forced the issue to re­main un­re­solved. In his dis­sec­tions of cap­tured spec­i­mens, Steller (1751) also noted the pres­ence of white, par­a­sitic worms in the gut. It has been sug­gested that these par­a­sites may have been as­carid ne­ma­todes, but the ab­sence of any pre­served spec­i­mens pre­vents a def­i­nite iden­ti­fi­ca­tion.

Hu­mans are the only known preda­tors of Hy­dro­damalis, al­though Domn­ing (1978) sug­gested that sharks and killer whales were also likely preda­tors.

Con­trib­u­tors

Bret We­in­stein (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, James Pat­ton (au­thor), Uni­ver­sity of Cal­i­for­nia, Berke­ley, James Pat­ton (ed­i­tor), Uni­ver­sity of Cal­i­for­nia, Berke­ley.

Ref­er­ences

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

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

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

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

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

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

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.