Table l .—Estimated numbers of male pups (born, dead, and livmg at the time of migration! and age-specific commercial kill of males 

 from the 1950-70 vear classes on St. Paul Island, Pribilof Islands. Alaska.' 



'Sources tor data in Table 1 and tootnotes are given belov^r 

 Pups born 1 950-60 table 1 1 2 Irom Ctiapman 1 1 973) . 1 961 -65 and 1 969-70, table 1 4 from Marine Mammal Biological Laboratory ( 1 971 ■). 1 967-68, table 1 from 



l^anne lulammal Division (1976^) A 1 1 sex ratio is assumed (Kenyon et al 1954, H Kaiimura pers common ) 

 Dead pups 1 950-60 (except 1 952), appendix table 39 from Marine Mammal Biological Laboratory ( 1 961 ) . 1 952, counts (Irom same source) on sample rookenes 



only, extrapolated to island total Irom average contribution ol these rookeries to known totals in 1951 and 1953 1961-69 table A.12 Irom Manne Mammal 



Biological Laboratory (1971) A 1 1 sex ratio is assumed (Kenyon et al 1954, M C Keyes pers common ) 

 Living pups Pups born less dead pups, rounded to nearest thousand 



Kill by age 1950-56 year classes, table 1 trom Marine Mammal Biological Laboratory (1961'), 1957-64 year classes, table 1 trom Manne Mammal Biological 

 Laboratory (1971), 1965-70 year classes table 1 from Marine Mammal Division (1976^) 



"Marine Mammal Biological Laboratory 1 971 Fur seal invesligation, 1 970 Unpubl manuscr , 1 55 p US Dep Commet . Natl Mar Fish Serv Northwest 



Fish Cent , Seattle, WA 98112 



"Marine Mammal Division 1976 Fur seal investigations, 1975 Unpubl manuscr , 1 15p US Dep Commer Natl Mar Fish Serv , Northwest Fish Cent , 



'Marine Mammal Biological Laboratory 1961 Fur seal investigation, Pribilol Islands, Alaska Unpubl manuscr , 148 p US Fish Wildl Serv , Bur 

 Commer Fish 



1950). However, the average numbers of pups 

 migrating from land and of seals harvested at age 

 Syr are approximated for the 1920-22 year classes 

 in order to include in the yield-pup relationship a 

 data point for the relatively small pup population 

 then present. It should be mentioned that basic 

 data were not taken during 1925-46 from which to 

 estimate annual pup production. 



The 1920-22 averages are based on kill data 

 from Lander and Kajimura^ and on pup data from 

 Kenyon et al. ( 1954). The average number of pups 

 born annually on St. Paul Island during 1920-22 

 was approximately 150,700. Their mean mortality 

 rate on land was 2.2'7f , so an average of about 

 74,000 male pups migrated to sea annually. Be- 

 cause the harvest always has been selective for 

 animals the size of 3- and 4-yr-olds, these 1920-22 

 year classes contributed to the kills mainly in 

 1923-26. The annual average kill then was 14,300, 

 of which about 9,100 were age 3 yr assuming the 

 same average (64'7f ) as in the kills from the 1950- 

 70 year classes (Table 1). 



'Lander, R. H, and H Kiyimura, 1976 Status of northern 

 fur seals. Food and Agriculture Organization of the United 

 Nations, Scientific Consultation on Marine Mammals, Bergen, 

 Norway, August 31-September 9, 1976, 50 p. (Unpubl. rep. I 



The kill of 3-yr-olds is used as an index of abun- 

 dance at that age. The assumption is justified 

 reasonably well by the generally stable harvest- 

 ing regime and the usual predominance of this age 

 group in the kills. 



Annual population monitoring and behavioral 

 data (Bartholomew and Hoel 1953; Peterson 1968) 

 show the median date of birth on St. Paul Island is 

 about 8 July, pup mortality on land is essentially 

 over by mid-August, and the median date when 

 pups migrate to sea is around 1 November. Survi- 

 val of pups on land is calculated as the ratio of 

 living pups to pups born (Table 1). 



Few seals haul out on land until 24 mo of age, 

 and survival is estimated for the first 20 mo at sea. 

 These ocean survival rates are calculated from the 

 data for living pups and age-specific kills (Table 1) 

 and from the model of Lander (1975) with time 

 intervals appropriately modified. 



Results 



Figure 1 shows wide fluctuations in the kill at 

 age 3 yr around the regression line for pups born. 

 After the effects of pup mortality on land are re- 

 moved, high variability persists around the line 



312 



