ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 17 



Fig. 11. Walruses sighted in August (symbols as in Fig. 4). 



September (Fig. 12) 



The pack ice usually retreats to its least extent in September, and the mean 

 position of its southern edge at that time in the central Chukchi Sea is about 

 74°N. To the east and west, the edge is substantially farther south, and there is 

 some formation of new ice, especially in the East Siberian and Beaufort seas. 



Apparently, most of the walrus population at this time is situated north of 

 70°N. In years when the ice retreats far to the north, the animals haul out on 

 Wrangell Island in enormous numbers, particularly at Cape Blossom (Gol'tsev 

 1968; Tomilin and Kibal'chich 1975). A large number of animals remains along 

 the northern coast of Chukotka and in the vicinity of Barrow. Other herds are 

 distributed along the fringe of the pack between Barrow and Wrangell Island 

 but are concentrated mainly east of 170°W and west of Herald Island (Estes and 

 Gilbert 1978; J.J. Burns, personal communication). To the south, large herds of 

 males remain on Big Diomede (Ratmanov) Island and on the Arakamchechen, 

 Rudder, Meechken, and Round Island hauling grounds. In some years, 

 individual migrants first appear in late September at St. Lawrence Island and on 

 the coast of western Alaska between the Kuskokwim and Yukon deltas. 



The western, northern, and eastern limits of distribution in the northern part 

 of the range in September have been established respectively, by sightings at 

 70°24'N, 166°55'E and near Cape Shelagskii in the East Siberian Sea 

 (Anonymous 1965), at 75^35^, 179^58^ and at 75°52'N, 164^15^ in the 

 Arctic Ocean (Krylov 1968; C. A. Barnes, personal communication), and at 



