checkmark (see section on Tags vs. Other 

 Marks). The opposite was true, however, for 

 2-year-old males of the 1965 year class re- 

 covered in 1967 and those of the 1966 year 

 class killed in 1968. 



Estimates of the pup population from inarked 

 fen-iales are higher than those from marked 

 males but decrease at a similar rate by year 

 class (tables 17 and 18). Estimates from re- 

 coveries of marked females vary considerably, 

 according to age at recovery, probably be- 

 cause females that lose their tags cannot be 

 identified accurately as to year class except 

 for those in ages 2, 3, and 4. In addition, the 

 number of females killed in each of these age 

 groups is small. The estimates from re- 

 coveries of females are probably biased, so 

 the data for the sexes were not combined to 

 provide a pooled estimate. Generally, the use 

 of con^bined data would produce estinnates 

 slightly greater than those based only on re- 

 coveries from males. 



Because most or all of the nnortality of pups 

 on land occurs before marking, the number of 

 dead pups counted was added to population 

 estimates "at the tinne of marking" to obtain 

 the total number of pups born for each year 

 class. For reasons discussed previously, 

 the most reliable estimates of the number of 

 pups at the time of marking based on the 

 recovery of marked males are believed to be 

 at ages 3 and 4. According to the estimates, 

 the total number of pups born has decreased 

 each year since I960 (table 20). 



The pup population on four rookeries was 

 estimated by shearing and sampling (Chapman 

 and Johnson, 1968). Three rookeries were 



Table 20. — Estimates of the seal pup 



population, year classes 1960-65, at time 

 of tagging from recoveries of marked male 

 seals in ages 3 and -4, and the count of 

 dead pups, Pribilof Islands, Alaska 



Year 

 class'^ 



Estimate of 



pups at time 



of tagging 



Count of 

 dead pups 



Total pups 

 born 



1960 

 1961 

 1962 

 1963 

 1964 

 1965 



Number 



568,000 

 489,000 

 -430,000 

 407,000 

 395,000 

 351,000 



Number 



75,000 

 71,000 

 54,000 

 39,000 

 25,000 

 46,000 



Number 



643,000 

 560,000 

 484,000 

 446,000 

 420,000 

 397,000 



■"■ Estimates for year classes 1960-64 were 

 from seals marked by tagging. 



^ Estimates from recoveries of 3-year-old 

 males marked by tagging and by removing parts 

 of flippers . 



sampled four times, and one was sampled 

 twice (table 21). The total of the mean estimate 

 for the four rookeries was 27 percent lower 

 than that obtained last in 1966 (table 22). 



The number of pups countedontwo rookeries 

 in 1968 (table 23) changed little since 1966. 

 The number on Morjovi Rookery was 4 percent 

 less in 1968 than in 1966, and the number on 

 Zapadni Reef Rookery was about 4 percent 

 higher. According to estimates based on shear- 

 ing and sannpling, 17 percent fewer pups have 



Table 21. — Estimates of the seal pup population. 



year class 1968, from shearing and sampling on selected rookeries, 

 St. Paul Island 



- Number - 



First count 



Morjovi 2,529 106 380 2,650 17,636 64 270 1,600 U,987 



Reef 4,216 125 547 3,125 24,086 75 324 1,872 24,359 



Vostochni^... 5,581 — — — ~ 115 464 2,875 34,581 



Zapadni Reef. 721 19 78 475 4,391 17 68 425 4,506 



Second count 



Morjovi 2,529 101 393 2,525 16,249 56 238 1,400 14,876 



Reef 4,216 90 352 2,250 26,949 60 264 1,500 23,955 



Vostochni^... 5,581 — ~ — — 104 454 2,600 31,962 



Zapadni Reef. 721 15 64 375 4,225 13 46 325 5,094 



~^ ; where N=:estimates of the pup population at time of shearing; M=number of pups sheared; C=number of pups 

 counted during sampling; and R=number of sheared pups counted during sampling. 

 ^ Pups v(ere not sampled on Vostochni Rookery 17 August. 



18 



