ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 163 





Table 26. Depth and duration 



of feeding dives of walruses. 













Surface: 







Number of 



Mean duration (min/s) 



subsurface 





Depth (m) observations 



Surface 





time ratio 



Source^ 



6.4 



10 



2/08 



2/01 



1:0.9 



NY 



8.2 



4 



2/26 



4/59 



1:2.0 



NY 



9.0 



20 



2/28 



4/46 



1:1.9 



NY 



12.1 



8 



2/48 



4/53 



1:1.7 



NY 



40 



?b 



0/55 



5/0 



1:5.4 



TK 



40 



20c 



1/04 



8/20 



1:7.8 



TK 



55 



2 



0/52 



5/38 



1:6.5 



U 



79 



12 



1/34 



7/46 



1:5.0 



FE 



aPE = F. H. Fav and J. A. Estes (unpublished data), NY = Nvholm (1975), TK = Tomi- 

 lin and Kibal'chich (1975), U = F. H. Fay (unpublished data). 

 ^Number of observations not given. 

 ^Approximate; exact number not given. 



Pacific walruses in general tend to ventilate at the surface for about 1 min, after 

 every 5 to 8 min of subsurface activity. 



The maximum depth at which walruses can feed, according to Vibe (1950) is 

 about 80 m. Although many have been sighted in deeper waters of the Bering 

 and Chukchi seas, none have been identified as feeding at depths greater than 

 79 m. 



Search for Food 



Nearly all of the invertebrates that are eaten by the walrus reside on or at very 

 shallow depths within the surface of the benthic sediments. Hence, most of them 

 are readily accessible without extensive digging or plowing of the bottom. 

 Because these prey are not uniformly distributed, the walrus must have the 

 ability to locate clumps or "patches" of suitable prey and by tactual or visual 

 means to distinguish them from other organisms and from inanimate objects. 



Johansen (1912:214) claimed to have observed walruses in search of food 

 under natural conditions, presumably having viewed them from above as they 

 dove in clear, shallow water. Unfortunately, his description of their methods is 

 somewhat ambiguous, for he stated that, "with regard to the manner in which 

 the animals obtain their food, it was observed that they sink down to the bottom 

 in a sloping direction (the front end downmost), until they almost stand on their 

 head; they then move backwards ploughing the bottom with their tusks." I have 

 added the italics since the meaning of this statement is dependent on inter- 

 pretation of "backwards" in this context. One must mentally "stand on his head" 

 to recognize that it could mean dorsally (literally "toward the back"), whereby 

 the tusks would have been "ploughing the bottom" by being dragged through it, 

 rather than thrust point-first into the sediments. 



That the animals generally move snout-first along the bottom, dragging their 

 tusks, rather than moving posteriad, digging or plowing with the tusks, is 

 indicated by their method of propulsion with the hind limbs, patterns of 

 abrasion on the tusks, and vibrissae, and by the search behavior of captive 



