156 



NORTH AMERICAN FAUNA 74 



most abundant. Worms, including Priapulus, Echiunis, and two kinds of 

 polychaetes, were rated second in importance; arthropods were rated third, and 

 "ascidians," including Pelonaia and Cucumaria (an echinoderm) were rated last, 

 since "they were found only in insignificant quantities." Nikulin gave no 

 indications of the sex or age of the consumers or of the specific locations in which 

 they were taken, and he provided no data on the frequency of occurrence, 

 w^eights, or volumes of the prey. 



In Krylov's (1971) material from 35 walruses taken in the vicinity of Wrangell 

 Island (presumably in July and August) in 1960 and 1963, moUusks were most 

 frequently recorded and apparently were the most significant prey in terms of 

 volume. However, these were mainly the smaller forms Macoma, Niwula, 

 Yoldia, and Margarites. Of secondar\' importance in abundance and volume 

 were Priapuhis, gammarid amphipods, crabs, the bivalves Mactra sp. and 

 Thyasira flexuosa, holothurians, and Pelonaia. Tomilin and Kibal'chich (1975) 

 reported that they found the principal foods of walruses in this area in 1972 and 

 1973 to be Priapuhis, Mija, and Ampelisca macrocephala. 



Autumn: St. Lawrence Island. — There are no data on the feeding habits of the 

 Pacific walrus during the southward migration in autumn. However, the St. 

 Lawrence Islanders repeatedly told me during the 1950's that Tethyum 

 aurantium (local name oh'pah) often made up a major part of the stomach 

 contents during October-December, whereas it did not occur in other seasons. 

 This suggests a seasonal change in either the feeding habits of the walruses or the 

 availability of this and other prey. 



General observations. — In all seasons and all areas, bivalve mollusks occurred 

 most frequently in the stomach contents, but it is not clear in all instances 

 whether they usually made up the greatest proportion by weight. Krylov (1971) 

 reported that mollusks made up 1 .59 of 2.58 kg (62 % ) of the stomach contents of 

 one animal in the Wrangell Island area in summer; Fay et al. (1977) recorded 

 that mollusks made up 665.4 of 694.6 kg (96%) of the identifiable organic 

 matter in the stomachs of 107 animals taken in the St. Lawrence Island to Bering 

 Strait region in spring. 



In general, the analyses of stomach contents have indicated that walruses are 

 highly selective in their feeding. Although the stomachs of animals taken in a 

 given area tended to contain a few examples of most of the macrofaunal inver- 

 tebrates known to occur there, they did not contain anything approaching a 

 representative sample of the local fauna (Vibe 1950; Fay et al. 1977). Some 

 organisms such as the very abundant brittle stars (Ophiuroidea) were not repre- 

 sented at all, whereas the larger bivalves in particular were overrepresented. 

 Swift, elusive prey, such as fishes, shrimps, and cephalopods were scarce. 

 Apparently, female walruses tend to select smaller prey than do males, for Fay et 

 al. (1977) found that the unit weight of food items in stomachs of adult males 

 was 5 to 10 times greater than in adult females. 



Flesh of other pinnipeds has been found frequently enough (1 to 11 %) in the 

 stomach contents of walruses throughout the Arctic to indicate that it is an 

 important complement to the basic molluscan fare Qohansen 1912; Gray 1927; 

 Pedersen 1931; Chapskii 1936; Tsalkin 1937; Nikulin 1941; Vibe 1950;'Brooks 

 1954; Mansfield 1958a; Loughrey 1959; Shustov 1969; Kr\'lov 1971; Fay et al. 

 1977). Chapskii (1936) and Vibe (1950) presumed that walruses eat seals only 



