240 



NORTH AMERICAN FAUNA 74 



evidence at present on which to base estimates of mortahty, which probably 

 differ widely between years and between the different sex and age classes. 



Population 



The world population of walruses in 1978 probably included more than 

 200,000 animals, about 80% of which were in the North Pacific (Bering-Chuk- 

 chi) region. The actual numbers are unknown but certainly were in that order of 

 m.agnitude. Clearly, these animals were much less numerous than they had been 

 a few centuries earlier. In all parts of their distributional range they were 

 severely depleted by commercial exploitation at various times during the past 350 

 years. Although protected to some degree in all areas in recent years, the North 

 Atlantic populations still have not recovered. Only the North Pacific population 

 appears to be approaching its pre-exploitation level. 



The history and current status of walrus populations in the North Atlantic 

 region and in the Laptev Sea were reviewed by Reeves (1978). In this chapter, 

 my principal objective is to summarize briefly the known history and vital 

 statistics of the North Pacific population. 



Identity 



The walrus appears to be a relative newcomer to the North Pacific region, for 

 the fossil evidence of its presence there dates back no more than about 100,000 

 years to the middle Pleistocene (Sangamon) interglacial stage (Hopkins 1967; 

 Repenning and Tedford 1977). At that time, climate and sea temperatures in 

 Beringia apparently were somewhat milder than at present, and sea ice in winter 

 extended no farther southward than the vicinity of Bering Strait (Hopkins 1972). 

 I presume that walruses first entered the area at that time from the northwest, 

 having traversed the northern coast of Eurasia from the North Atlantic region. 



At present, walruses are essentially circumpolar in distribution (Scheffer 

 1958), but they are not uniformly distributed. There are several areas of 

 concentration, between which few or no walruses have been sighted in recent 

 times (Fig. 3). This discontinuity suggests the presence of several discrete 

 populations which have little or no chance of interbreeding. The present 

 isolation of some of those populations probably resulted from depression of their 

 numbers by overharvests. Differences in body and tusk size between some 

 regional concentrations, however, even as close as Hudson Bay and Foxe Basin 

 (Mansfield 1958a), suggest longer reproductive isolation. 



Walruses of the Bering-Chukchi region differ from those of the Laptev Sea 

 principally in size (Heptner et al. 1976), and these two populations are physically 

 separated by at least 1,200 km of unoccupied or sparsely occupied sea. 

 Individuals and small groups occasionally stray from the Chukchi Sea as far west 

 as the mouth of the Kolyma River and Bear Islands (Chapskii 1940; Nikulin 

 1941), but strays from the Laptev population have been sighted no closer than 

 the eastern part of the New Siberian Islands, some 350 km away (Chapskii 1940; 

 Popov 1960fc). Hence, there appears to be little if any possibility of extensive 

 interchange between the Laptev and Pacific populations. 



