ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



161 



at that time were the adult males (25/62 = 40%); those least often containing 

 food were the adult females with newborn calves (3/46 = 6%). All others were 

 intermediate between those extremes (6/27 = 22%). Because a large proportion 

 of the adult males remains in the Bering Sea throughout the summer, 

 presumably continuing to feed intensively, the resources of the summering areas 

 in the Chukchi Sea are available mainly to the females and young. 



Feeding Behavior 



Feeding Rhythm 



Loughrey (1959) reported that the walruses in Hudson Bay seemed to feed 

 mainly in the early morning hours, whereas Vibe (1950) indicated that their 

 feeding schedule in summer in northwestern Greenland was linked more with 

 the tides. Tomilin and Kibal'chich (1975) and Nyholm (1975) observed walruses 

 feeding at various times during the day and night. During more than 50 whaling 

 and walrus hunting trips with the St. Lawrence Islanders in March to June, I 

 sighted walruses in the water more often in the morning and evening than at 

 other times, and observed that those taken in early morning and late evening 

 most often had food in their stomachs. 



Fay and Ray (1968) recorded the diurnal activity schedule of walruses in 

 captivity, thinking that it might resemble that of the free-living animals. Their 

 data indicated two peaks of activity in the water, one in mid-morning to late 

 morning, and the other in late afternoon and evening. Comparative data from 

 sightings of walruses during shipboard and aerial surveys, however, have not 

 confirmed that pattern (Fig. 101). Although each curve suggests that there are 

 two or three periods per day when the animals tended to be in the water 

 (principally feeding?), none of the curves closely resembles any of the others in 

 regard to the timing of those periods, and none resembles the pattern shown by 

 the captives. Thus, it seems that the Pacific walrus does not have any regular diel 

 periodicity that could be related to feeding, possibly because the prey are 

 relatively immobile and not rhythmic in availability. 



Depth and Duration of Feeding Dives 



The duration of feeding dives presumably is a function of the water depth and 

 abundance of food, as well as the capability of the diver. The observations 

 reported thus far seem to bear that out. Nyholm (1975) recorded the surface and 

 subsurface times of walruses during 42 feeding dives at depths ranging from 6.4 

 to 12.1 m. In the shallowest water, the mean subsurface time was 2 min and the 

 surface time about the same. In the deeper water, the animals were beneath the 

 surface for nearly 5 min, and 2.5 min at the surface between dives. Freuchen 

 (1935) observed two walruses feeding in water that was about 10 m deep and 

 noted that they remained beneath the surface for 2 to 3 min per dive. 



Tomilin and Kibal'chich (1975) reported that walruses feeding near Wrangell 

 Island did so in groups of two or three animals, which dove and surfaced in 

 unison. They watched one pair feeding in 40 m of water for about 4 h, during 

 which the dives ranged in duration from 6 min 3 s to 9 min 7 s, and the surface 

 intervals between dives were from 55 to 77 s. The dives of another feeding pair 



