PEREZ and MOONEY: LACTATING NORTHERN FUR SEALS 



on data for pregnant females, after excluding fetal 

 mass, which we used to represent body mass of lac- 

 tating females prior to parturition. Figure 3 shows 

 that this loss in body mass occurred for all ages. 



60 



50 - 



40 



E 30 



20 



10 



 Pregnant 

 ▲ Lactating 



10 

 Age 



15 



> 18 



Figure 3.— Mean body mass (minus stomach contents and fetal 

 mass) of pregnant (prepartum) and lactating (postpartum) female 

 northern fur seals by age taken pelagically in the eastern Bering 

 Sea and western Alaska during June and July respectively 

 (1958-74). 



Relative Food Intake 



We found a significant difference (P < 0.05) in the 

 relative magnitude of food consumption between lac- 

 tating and nonlactating female northern fur seals 

 during July-September, but not October, and Figure 

 4 shows the relative percentage frequency of the 

 number of lactating and nonlactating adult females 

 showing different masses of stomach contents dur- 

 ing July-September (pooled data). It is apparent that 

 a greater proportion of lactating females contained 

 food in their stomachs. Lactating females signifi- 

 cantly (P < 0.001) ingested more food because they 

 had lower cumulative percentages of empty stom- 

 achs and stomachs with smaller quantities of food 

 than did nonlactating females. 



Table 2 presents the results of analyses between 

 lactating and nonlactating females for the July- 

 September period by time of collection during the 

 day. Our calculated values of the index of relative 

 food intake after sunrise were 162% during 0-3 h, 

 166% during 4-7 h, 537% during 8-11 h, and 585% 

 during 12-15 h (P < 0.05). The calculated index 

 values during 8-15 h after sunrise are excessive, 

 presumably an artifact of food digestion in the 

 stomach. 



c 



01 



u 



c 



01 



a. 



>■ 

 u 

 c 

 01 



3 



or 



01 



> 



45 



40 - 



35 



30 - 



25 



£ 20 - 



75 15- 



10 



 Lactating (N=981) 



"J Nonlactating (N=2513) 



ri rl J 



rl •* J LM 



hi [■ tH- ■" "■» i" ' " i " — ' '" " 



o 



A 



Total mass of stomach contents (kg) 



Figure 4.— The relative percentage frequency of lactating and nonlactating female northern 

 fur seals (age >4 yr) by total mass of stomach contents during July-September. 



375 



