24 



NORTH AMERICAN FAUNA 74 



Fig. 17. Distribution of sightings of walruses (all months, 1930-79) in relation to the 

 position of the 100-m isobath in the Bering-Chukchi region. Each dot represents one 

 sighting, regardless of the number of animals. 



Even when the eastern and western passages are open beyond Barrow and Long 

 Strait, however, only a few animals stray outside the area bounded by 155 °W 

 and 175°E longitude (Figs. 11 and 12). The failure of more animals to move into 

 the Beaufort and East Siberian seas in late summer is somewhat of an enigma but 

 suggests that the conditions (food?) there are not satisfactory for walruses or, at 

 least, are less satisfactory than those west of Barrow and near Wrangell Island. 



There seem to be no physical limits to distribution of walruses south of the 

 Bering Sea, except that the continental shelf is much narrower and the climate 

 much warmer than to the north. Benthic invertebrates are abundant in the 

 sublittoral and shoal waters of the North Pacific Ocean, and many of the same 

 species of mollusks that are ordinarily eaten by walruses occur as far south as 

 Fuget Sound and Japan (MacGinitie 1959). The possibility that climate is the 

 principal limiting factor was investigated by Fay and Ray (1968) and Ray and 

 Fay (1968) with inconclusive results, but there were numerous suggestions of 

 negative response to solar radiation and air temperatures exceeding those in the 

 southern Bering Sea. During warm summer days at Round Island, the animals 

 on the hauling grounds tend to remain at the water's edge or offshore, apparently 

 in response to excessive heat on the beaches (Miller 1975a, 1976, and unpublished 

 data). 



Canadian biologists have indicated that the traditional hauling grounds in 



