related differences in loss of tags or mor- 

 tality) in the early and late groups in 1964. 

 Tags used in August were attached at the 

 hairline, whereas those used in September 



were attached between the fourth and fifth 

 digits (fig. 13). Both groups of tags used in 

 1963 were attached to the rear edge of a front 

 flipper at the hairline. 



POPULATION ESTIMATES 



This section presents estin-iates of the size 

 of various segments of the population based on 

 the most recent data. Methods used and sources 

 of data have been described by Roppel, John- 

 son, Bauer, Chapman, and Wilke (1963); Roppel, 

 Johnson, and Chapman (1965); and Roppel, 

 Johnson, Anas, and Chapman (1965 and 1966). 



NUMBER OF PUPS BORN 



The size of each year class at birth is 

 estimated from recoveries of tagged and 

 marked seals and from marked-to-unmarked 

 ratios obtained in the year of birthby shearing 

 and sampling live pups. 



Estimates Based on Tag Recoveries 



Estimates of the pup population based on 

 tag recoveries (including seals that lost their 

 tags) from male seals are presented in tables 

 13, 14, and 15. The estimates based on tag 

 recoveries from 3- and 4-year-old males by 

 S-day periods were reasonably consistent 

 (table 13). The estimated number of pups born 

 has steadily decreased from 643,000 in I960 

 to 440,000 in 1964 (table 15). 



The ratio of tagged to lost-tag seals re- 

 covered in 1966 was higher on St. Paul Island 



than on St. George Island. An adjustment in the 

 number of lost-tags recovered on St. George 

 Island, however, was not made because of 

 uncertainty as to whether the difference was 

 real or was caused by incomplete recovery of 

 seals that had lost their tags. 



Estimates Based on Shearing and 

 Sampling Live Pups 



Fur seal pups have been marked on St. Paul 

 Island each year since 1963 by shearing a 

 patch of fur from the top of the head, and 

 groups of 25 pups have been later sampled to 

 obtain marked-to-unmarked ratios for esti- 

 mating the number of pups born. The program 

 was extended to St. George Island and Sea Lion 

 Rock in 1966. Tagged-to-untagged ratios for 

 estimating the number of pups born were 

 obtained on St. Paul Island in 1961 and 1962. 

 The sampling stations have been permanently 

 marked on St. Paul Island rookeries by 

 91.4-cm. (3-foot) steel stakes set 23.1 m. 

 (25 yards) apart in concrete or rock. On St. 

 George Island and Sea Lion Rock we selected 

 stations by pacing or by visually estimating 

 distances during sampling. 



A total of 30,942 pups were marked by 

 shearing in 1966. The pup population on St. 

 Paul Island was sampled twice to obtain a 



Table 13. --Estimates of the pup population based on tag recoveries from 3- and 4-year-old male 

 seals, by 5-day periods, year classes 1962-63, Pribilof Islands, Alaska 



Ags 3 (year class 1963) 



Age 4 (year class 1962) 



Population Population 

 Date Killed Tagged Tag estimate at Killed Tagged Tag estimate at 

 recoveries time of tagging recoveries time of tagging 



Number Number Number 



July 

 6-11 4,790 24,971 



317 



Number 



376, 229 



Number Number Number 



4, 578 49, 908 



605 



Number 



377, 118 



12-16 



3, 636 



203 



445, 212 



2, 695 



322 



416, 578 



17-21 5,515 



22-26 5,437 



27-31 6,399 



Aug. 



1-5 5,329 



Total 31, 106 



179 



443, 913 



1, 953 



409, 463 



21 



