Table 21. --A comparison of total pup counts on four rookeries with 

 pup population estimates from marked to unmarked ratios, St. 

 Paul Island, year class 1964 



Rookery- 



Percent 

 Estimated pup population error in 

 Count 8-9 15-16 Mean mean of 

 Aug. Aug. estimates 



Kitovi Amphitheatre 1, 095 



Little Polovina 7, 180 



Morjovi 

 Zapadni Reef 



17, 530 



5, 700 



1,522 1,243 1,382 +26 



8, 640 8, 130 8, 385 +17 



17,300 16,460 16,880 -4 



6, 130 6, 900 6, 515 +14 



1 Rocky Point south of Sea Lion Neck not included. 

 Count corrected by adding 400 pups estimated to have swum out 



of the rookery area. 



uncounted areas, the total pup population can 

 be estimated from the counted pups and the 

 harem bull count, that is, 



31,505 . N 

 1,222 - 11,074 



N = 285,000 



where 



31,505 

 1,222 



11,074 



is the number of pups counted 



is the harem bull count on areas 



where pups were counted 

 is the total count of harem bulls 



for both islands 



and 



N is the pup population 



The areas where pups were counted contained 

 11.0 percent of the total number of harem bulls 

 on both islands. 



Discussion of the Estimates of the Pup 

 Population . --Recent estimates of the pup popu- 



lation from tag recoveries are lower than 

 those of the mid- and late-1950's. Since 1960, 

 the pup population has also been estimated 

 from marked to unmarked ratios obtained from 

 sampling live pups. The estimate obtained in 

 I960 was based on samples from only two 

 rookeries; since 1961, all rookeries have 

 been sampled. Where the results of the two 

 methods (tag recoveries and sampling) can 

 be compared, the estimates from sampling 

 are lower than those from tag recoveries 

 (table 24). 



Attempts to check the accuracy of the esti- 

 mates from sampling by counting live pups 

 have been partially effective in that total pup 

 counts were successfully made on one rookery 

 in 1963 and on three rookeries in 1964. From 

 the counts and sampling estimates it is im- 

 possible to derive a correction "factor that 

 can be used to improve the estimates. A 

 correction factor may not, however, be needed. 

 The counts show that it is highly improbable 

 that the estimated pup population from sam- 

 pling could be drastically in error. Hence, 

 the best estimate of the 1964 pup population 

 is about 350,000, that is, 328,000 plus pup 

 mortality on land. 



19 



