-51- 



4) Weddell Seals 



Annual movements of Weddell seals are poorly known. 

 Smith (1965) felt that 85% of the McMurdo Sound population 

 migrated northward into pack ice regions during the winter. 

 However, Stirling (1969c) , Lindsey (1937) , and Bertram 

 (1940) stated that evidence indicates that most McMurdo 

 Sound Weddell seals remain and winter under the ice. In the 

 spring, pupping occurs on the fast ice in traditional haul- 

 out areas (Stirling, 1969c) . 



c. Stock Identification 



There may not be well segregated stocks within pack 

 ice seal species (Seal et al., 1971b) as a result of 

 potential mixing effect of the pack ice on the population 

 genetics of crabeater, leopard, and Ross seals. Tagging 

 studies on Weddell seals in McMurdo Sound have indicated 

 that individuals either remain in an area year-round or 

 return annually to the same haul-out areas (Stirling, 1969b, 

 1969c; DeMaster, 1978) . This site fidelity may lead to the 

 development of subgroups of Weddell seals at certain locations 

 Studies of gene frequencies in Weddell seals sampled at 

 widely separated localities substantiate this idea 

 (Shaughnessy, 1969; Seal et al., 1971a). 



d. Standing Stock 



Various estimates of abundance for the four true 

 Antarctic seals are given in Table 8. Recent census efforts 

 of Antarctic seals (Erickson et al., 1971; Gilbert, 1974; 

 Hofman, 1975; Gilbert and Erickson, 1977) have improved 

 earlier estimates of the abundances of Antarctic seals 



(Scheffer, 1958; Ecklund, 1964) . Estimates vary because 

 of the logistic difficulties in censusing and because daily 

 activity patterns and haul-out timing may strongly affect 

 them. For example, Siniff et al. (1970) and Erickson et al. 



(1971) pointed out that the crabeater seals' definite 24 hour 

 activity pattern affects haul-out timing and accuracy of 

 aerial estimates of abundance. Siniff et al. (1971) found 

 the same true for Weddell seals which haul out mostly 

 between 1100 and 1600 hours. Differences in activity 

 patterns and haul-out rates must be considered when inter- 

 preting aerial survey or other census results. 



e. Food Habits 



Delineating the impact of seals upon the ecosystem 

 requires far more than listing prey species. Factors such 

 as amounts of specific prey eaten, feeding rates, and 

 seasonal or age-specific shifts in food preference are all 



