Ecology and Biology of the Pacific Walrus, Odobenus rosmarus divergens Illiger

AbstractThe distribution, physical development, pelage, dentition, feeding behavior, reproduction, causes of mortality, and population structure of the Pacific walrus (Odobenus rosmarus divergens) were studied intermittently from 1952 to 1979. In winter, these animals tend to concentrate in north-central and southeastern Bering Sea, where sea ice conditions are most favorable for them. In summer, they concentrate mainly in northwestern and northeastern Chukchi Sea, along the edge of the ice. Most of the northward migrants are females and young; a large proportion of the adult males remains in the Bering Sea throughout the summer. Pacific walruses show strong sexual dimorphism; adult males are about 18% longer and 45% heavier and tend to have larger, more divergent tusks, as well as thicker, lighter-colored, and less hairy skin than adult females. As in other sexually dimorphic otarioid pinnipeds, males undergo secondary growth, beginning about the time of puberty and ending in full physical maturity about...