40 



z 

 < 

 in 



o 



20- 



PUPS BORN 



50 



•53 



90 150 210 



NUMBER OF MALE PUPS (THOUSANDS) 



FiGLTRE 1.— Yield-pup relation for male fur seals of the 1920-22 

 and 1950-70 year classes from St Paul Island Least squares 

 regression lines are shown for pups bom (a = 2.341. 6 = 0.126) 

 and for pups migrating from land (a = 3.740, b = 0.188). 



for pups migrating from land. Most of the varia- 

 tion in abundance at age 3 yr is evidently due to 

 changes in the ocean survival rate undergone by 

 the different year classes, not to changes in the 

 rate of pup survival on land. 



Estimated survival rates for the 1950-70 year 

 classes are in Table 2 (ocean survival could not be 

 estimated for the 1920-22 year classes without age 

 composition data). The means and ranges of survi- 

 val estimates in Table 2 are 87<7f ( 78-95'7f ) for pups 

 on land, 40% (18-497^ ) for the first 20 mo at sea, 

 and 35^?^ (14-45'7f ) for both stages between birth 

 and 2 yr of age. 



Figure 2 shows a statistically significant associ- 

 ation between the ocean and land survival esti- 

 mates (r = 0.67,P<0.01). Conditions of weather, 

 feeding, and disease which promote good survival 



Table 2. — Estimated natural survival rates of male fur seals 

 from St. Paul Island in two stages from birth to age 2 yr, 1950-70 

 year classes. 



Year 

 class 



< 

 o 45 



o 



5 35- 



25- 



Pups on 



land 



First 20 mo at sea 



until start ot kill 



at age 2 yr 



Birth to 

 age 2 yr 



78 86 94 



ESTIMATED SURVIVAL OF PUPS ON LAND (%) 



Figure 2. — Relation of estimated survival rate during first 20 

 mo at sea to estimated survival rate of pups on land for male fur 

 seals of the 1950-70 year classes from St. Paul Island. Functional 

 regression line shown (Ricker 1973) has intercepts = 0.830 and 

 slope [' = 1.425. 



of pups on land apparently equip them to survive 

 relatively well at sea. As in Figure 1, however, the 

 wide scatter about regression is prominent — 

 emphasizing again that events at sea contribute 



313 



