PEREZ and MOONEY: LACTATING NORTHERN FUR SEALS 



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Unimak Pass 



61° N 



59° 



57° 



55° 



53° 



51' 



177°W 



167° 



157 c 



Figure 1.— Locations where 3,494 adult female northern fur seals (ages >4 yr), whose data were analyzed in this study, were taken 

 by the United States and Canada in the eastern Bering Sea during July-September 1958-74. 



in the diet was determined by frequency, while the 

 ration of each species within only fish and squid was 

 determined by volume. Statistical comparison of the 

 diets of lactating and nonlactating females included 

 1) the Spearman rank correlation coefficient (Siegel 

 1956; Fritz 1974), 2) percentage similarity (Goodall 

 1973), and 3) 2 x 2 contingency table analysis (Zar 

 1974) on the number of stomachs with fish or squid. 



Feeding Time at Sea 



The largest breeding population of northern fur 

 seals (currently estimated at 8.7 x 10 5 for a declin- 



ing population; North Pacific Fur Seal Commission 

 1984) resides on the Pribilof Islands during the sum- 

 mer months. Pups first appear in late June (Bar- 

 tholomew and Hoel 1953) and the mean date of pup 

 birth based on recent data is 5 July (Gentry and Holt 

 in press); a date median between values cited by Bar- 

 tholomew and Hoel (1953) and Peterson (1968). 

 After this time, adult females spend a number of 

 days on shore in several visits to the islands during 

 June-November, and the intervening days between 

 these visits at sea foraging for food (Bartholomew 

 and Hoel 1953; Peterson 1968). They do not feed 

 daily. 



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