ECOLOGY AND BIOLOGY OF THE PACIFIG WALRUS 



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importance in the diet. Most common was the slender Thyonidium commune, 

 about 15 cm long and 2 cm in diameter, which usually was found intact in the 

 ingesta (Fig. 96d). Holothurians are mainly detritus feeders, living on or in the 

 surface sediments at water depths ranging from the littoral zone to more than 

 1,000 m. 



Urochordata. —Tunicates (sea squirts) of at least three genera were 

 represented in the ingesta and feces of walruses in the St. Lawrence wintering 

 area in north-central Bering Sea and in the Wrangell Island region of western 

 Ghukchi Sea. Most often and most abundantly represented in both areas was 

 Pelonaia corrugata (Fig. 96/). One other, Tethyum aurantium, is said by the St. 

 Lawrence Islanders to be common in the stomachs of walruses taken in autumn; 

 another species, probably of this genus, was found occasionally in stomachs of 

 walruses taken in both the St. Lawrence and Bristol Bay wintering areas. P. 

 corrugata is sessile on the surface of soft to sandy bottom sediments at depths 

 from the sublittoral zone to more than 100 m; Tethyum is an inhabitant of rocky 

 areas, mainly at lesser depths. 



Vertebrata. —The scarcity in walruses of endoparasites of known piscine 

 origin indicates that fishes rarely are ingested (Deliamure 1955; Deliamure and 

 Popov 1975). Only 2 of 240 stomachs from Pacific walruses that contained 

 identifiable foods had remains of fishes. These were eight blennies in one 

 specimen and two pricklebacks in the other (Krylov 1971). Although the arctic 

 cod, Boreogadus saida, is known to be eaten by Atlantic walruses (Homer and 

 Schaudin 1900 in Chapskii 1936; G. N. Safronova in Nikulin 1941; Pedersen 

 1962) and is abundant in the northern Bering and Chukchi seas, it has not yet 

 been found in any stomachs of Pacific walruses. 



Remains of two species of pinnipeds, the ringed seal {Phoca hispida) and 

 bearded seal, consisting mainly of pieces of skin and blubber with some muscles 

 and viscera, have been found with remarkable frequency (1 to 11%) in the 

 ingesta and feces of Atlantic and Pacific walruses. Probably, most of these seals 

 are taken as carrion, although it is conceivable that some are killed by the 

 walruses (Fay 1960; Krylov 1971). L. F. Lowry and K. J. Frost (personal com- 

 munication) found a walrus feeding on the carcass of a freshly killed spotted seal 

 pup {Phoca largha); they found comparable remains of another pup nearby. 

 Shustov (1969) reported the finding of spotted seal flesh in the stomach of a 

 walrus. 



Occurrence of the parasitic nematode Trichinella spiralis in 1 to 9% of 

 walruses from various parts of the Arctic (see review by Rausch 1970) may be the 

 result of their feeding on seals, especially bearded seals, for this is a parasite of 

 carnivores in which transmission usually is accomplished by ingestion of the flesh 

 of the prey by a predator. 



Other ingesta. — In addition to the items classifiable as food, the digestive tract 

 of the walrus usually contains a quantity of benthic sediments, apparendy 

 ingested incidentally. Such materials, ranging in size from fine sand to small 

 stones, made up nearly 2% of the total volume of ingesta in the walruses 

 examined by Fay et al. (1977), and varied in amount from a trace to 1.04 kg per 

 stomach. Other inanimate items in the same stomachs included a small piece of 

 seaweed (La mi nana sp.), a piece of broken glass, and a fragment of gasket 

 material from an internal combustion engine. 



