ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



229 



A, trichechi occasionally becomes superabundant on walrus calves in 

 captivity, where it is a major source of irritation as well as being unsightly. 

 Treatment with any of several formulations of "Dri-Die 67," a silica aerogel 

 sorptive dust, has been found effective in eradication of the lice (L. R. Penner 

 and W. P. Heuschle, personal communication). 



The nasal mite Orthohalarachne rosmari (Oudemans) has been recorded once 

 from a walrus that was captured in the vicinity of Franz Josef Land, northern 

 Barents Sea and held in captivity for 7 years in Hagenbeck's Tierpark, 

 Hamburg, Germany (Oudemans 1925). This mite has not been reported again 

 from walruses of either the North Atlantic or North Pacific regions. I searched 

 for nasal mites in the nasal passages and nasopharynx of about 25 walruses from 

 the Bering Sea but found none. 



Endoparasites 



The internal parasites of the Pacific walrus have been studied most intensively 

 by S. L. Deliamure and his students at the Crimean Pedagogical Institute, Sim- 

 feropol', USSR. A tabulation of recent findings in walruses from the Chukchi Sea 

 was provided by Yurakhno and Treschev (1972), and by Deliamure and Popov 

 (1975); their findings are reproduced in Table 38. 



Trematodes of the genus Orthosplanchnus occur frequently in the bile ducts of 

 the liver and rarely in the intestine; I have found them also in the pancreatic 

 ducts. In 2 of 222 walrus livers that I examined, an unusual abundance of these 

 trematodes was associated with fibrous thickening of the bile ducts, to the extent 

 that the liver was visibly and palpably "lumpy." Thickening of the ducts 

 (Fig. 131) presumably takes place in response to irritation caused by the 

 parasites, and this probably has some adverse influence on biliary function. 



Cestodes of the genus Diphyllobothrium, presumably acquired from ingested 

 fishes, occur infrequently and in small numbers. They localize in the small 

 intestine, where they seem to cause no appreciably irritative or other responses. 



The nematodes Contracaecum osculatum and Phocanema decipiem, also 

 probably acquired from fishes, typically localize in the stomach. In some 

 pinnipeds, they occur there in massive quantities, causing some destruction of the 

 mucosal layer and occasional ulceration of the stomach wall. However, in the 

 Pacific walrus, they are uncommon and, apparently, pathologically inconse- 

 quential. 



A third nematode, Trichinella spiralis, causes severe illness and death in man 

 and some other mammals as a consequence of massive larval invasion of the 

 musculature; its effect on walruses is unknown. Infective larvae of this parasite 

 have been found in skeletal muscles of 2 out of 131 walruses taken in the Bering 

 and Chukchi seas (Rausch et al. 1956; Fay 1960; Yurakhno and Treschev 1972) 

 and in comparable proportions from the North Atlantic region (Fay 1960; 

 Rausch 1970). 



Acanthocephalans are the most common internal parasites of the Pacific 

 walrus, usually localizing in the lower (ilial) part of the small intestine and in the 

 colon. The one species identified, Corynosoma validum, probably is acquired 

 through ingestion of an invertebrate intermediate host. In my experience, these 

 helminths usually are not very abundant and seem not to cause any significant 

 inflammation or other responses. 



