Table 20. --Estimates of the pup populations based on tag recoveries 

 from females, Pribilof Islands, Alaska, year classes 1958-62 



Killed 14-29 Tagged and tag- Population 

 Year August Tagged lost seals recovered estimate 

 class (n) (t) (s) (N) 



n = number of females killed from each year class, 14-29 August 

 1964. 



t = number of tags applied to each year class. 



s = number of tagged and tag-lost seals recovered from each year 

 class, 14-29 August 1964. 



N = estimated number of pups at time of tagging; 



(n+l)(t+l) 

 (s + 1) • 



Using the above information in the modified 

 Petersen formula, the number of yearling 

 males born in 1961 and still living at the time 

 of tagging in 1962 can be estimated: 



.. _ (600 + l)(28827 + l) 

 N (215 + 1) " 



80,211 



where 



600 is the number of tags applied to year- 

 ling males 

 28827 is the number of 3-year-old males 

 taken from 1 July through 7 August 

 1964 



and 



215 is the number of recovered 3-year- 

 old males tagged as yearlings 1 July 

 through 7 August 1964 



The estimate seems reasonable, but as pre- 

 viously mentioned, it may be slightly high. 



Estimated Pup Population From Sampling 

 Live Pups .-- The methods used in marking and 

 in sampling live pups on St. Paul Island in 

 1964 were the same as those used in 1963 

 (Roppel, Johnson, and Chapman, 1965), with 

 the following exception. Shearing effort was 

 distributed within each rookery according to 

 the counted distribution of the harem bulls on 



the rookery. This method gave a more uni- 

 form distribution of sheared pups than was 

 obtained in 1963. The number of pups sheared 

 was 27,716. 



All the live pups on three rookeries and a 

 separated section of a fourth were counted, 

 and the counts were compared to the estimates 

 obtained on each of the rookeries from sam- 

 pling (table 21). The estimates for the smaller 

 rookeries were higher than the counts, but 

 the estimate from the larger rookery was 

 slightly less. The total area counted contained 

 11.0 percent of the total number of harem 

 bulls on both islands. Though desirable, it 

 would be extremely difficult, if not impossible, 

 to count live pups on additional areas. 



The estimated pup population for each rook- 

 ery on St. Paul Island is given in table 22 

 for two sampling periods. The estimates from 

 pup sampling have been of about the same 

 magnitude since 1961 (table 23). To extend 

 the estimate to include the pup population of 

 both islands, the estimate for St. Paul Island 

 was divided by the usual factor of 0.8, giving 

 an overall estimate of 328,000. This estimate 

 does not include the pups that died prior to 

 shearing, something less than 25,000. 



Estimated Pup Population From the Count 

 of Pups on Four Rookeries .-- The count of 

 live pups on three rookeries and a portion of 

 a fourth can be used to estimate the total pup 

 population. Assuming that the ratio of pups 

 per harem bull is the same for counted and 



18 



