The Pacific walrus (Odobenus rosmarus divergens) : spatial ecology, life history, and population

Francis Hollis Fay
The Pacific walrus inhabits the Bering Sea during winter and the Chukchee Sea in summer, generally in close association with sea ice. The year-round northern limit to this range is marked by the southern edge of the relatively unbroken pack ice which, though not impenetrable, is usually avoided. The southern limit appears to be set by air temperatures, regions with monthly means of 50 F or more being unoccupied. Between these two "barriers," the animals frequent waters of less than 50 fathoms
more » ... s than 50 fathoms depth in which their preferred food, the pelecypods Mya, Saxicava, Astarte, Macoma, and Clinocardium occur. Seasonal migrations between the Bering and Chukchee Seas appear to be partly in response to changing physical conditions and partly due to an innate or learned behaviour pattern. Females are the most regular migrants; males are more subject to the inconsistencies of ice drift. The bull Pacific walrus reaches sexual maturity at six to eight years of age, the cow at five years of age. Breeding takes place mostly from April to June as the animals are migrating northward , and there is no evidence of any organized polygamy or "harem breeding." Gestation is one full year, and twinning is unknown. An individual cow rarely conceives in successive years, the first three pregnancies generally being at 2-year intervals and later ones three or more years apart. Males become senile at about fifteen years of age. Full adult body size is achieved at four to six years of age by both sexes, though growth continues slowly thereafter. The tusks and other teeth grow at a relatively high rate throughout the life span, and analyses of their structure and size have yielded good techniques for age determination. The population, upwards of 40,000 animals at present, has declined slightly in the past fifteen years, but it has reached or is approaching equilibrium. The birth rate and death rate are about equal, human predation accounting for most of the latter. Since the population is currently too small to satisfy the Alaskan Eskim [...]
doi:10.14288/1.0106248 fatcat:qv76gsfutffzxa3scwnft7mawm