ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



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autumn, the animals that come ashore during or following severe storms are said 

 by the Eskimos to be extremely lethargic and to strongly resist being driven back 

 into the sea. From this, the islanders have concluded that the walruses are physi- 

 cally exhausted from their long swim and require rest before continuing on their 

 way. In addition to being vulnerable to terrestrial predators (especially man), 

 animals in that condition may be predisposed also to contraction of infectious 

 diseases and to traumatization by other walruses. 



Damage by Rockslides 



Several of the hauling grounds used by walruses in the Bering-Chukchi region 

 are on beaches beneath high, rocky cliffs. Occasional landslides and falling rocks 

 from the cliffs apparently maim and kill a few animals. One example of this kind 

 of mortality was identified by B. P. Kelly and R. M. O'Connor (personal com- 

 munication) on Round Island in 1979. In that instance, an adult male with 

 crushed skull was found beneath a rockfall; a necropsy of the specimen revealed 

 no other plausible cause of death. Other examples have been recorded in the 

 same locality by J. Taggart and C. Zabel (personal communication) in previous 

 years. 



Overview 



The frequency of occurrence of pathological conditions and their effects on 

 walruses individually and as a population are not yet well documented. The evi- 

 dence at hand indicates, at least, that the causative factors are numerous and 

 that few of them are age- or sex-specific in their effects. For most of the past 120 

 years, the main mortality of walruses in the Bering-Chukchi region appears to 

 have been caused by man's harvests of these animals, for the population was 

 severely depressed at least twice during periods when harvest levels were 

 unusually high (see Population). An increasing body of evidence points as well to 

 a large, comparatively unnoticed natural mortality, which has been and still is 

 more difficult to evaluate. 



Presumably, the natural agents of morbidity and mortality described in the 

 foregoing account are the very ones that exerted a regulating influence on the 

 primitive population, before intensive harvesting began. Yet another agent, 

 malnutrition, may have been the proximate regulator, for the food supply is 

 finite and its replacement rate is comparatively low. The synergistic effects of 

 malnutrition with most of the natural agents mentioned here could cause 

 profoundly increased mortality. Malnutrition also probably depressed 

 reproduction. 



The overall rate of mortality from all causes was estimated by Burns (1965) as 

 being about 13% per year, based on the age composition of samples from the 

 harvest. Fedoseev and Gol'tsev (1969) believed that the basis for Burns' estimate 

 was unreliable and that the indicated rate was erroneously high. Harvest samples 

 generally are not representative of age composition, because of hunter selection 

 and the tendency for sex- and age-segregation in a nonrandomly distributed 

 population. Fedoseev and Gol'tsev (1969) speculated that actual mortality was 

 no greater than 8 to 10%, based on the maximum age of animals in the 

 population (about 40 years). Obviously, there is little agreement and no firm 



