
Pups 
Virtually all seals are born between mid-June and the end of 
July. The young fur seal is called a pup until it is 5 or 6 months 
old, at the end of December. Thereafter for 12 months it is called a 
yearling. The number of pups born each summer is an extremely important 
census figure for several reasons. (1) It is the only clue to the 
number of breeding cows. (2) It is an index of the reproductive status 
of both male and female elements of the herd. (3) Its fluctuations 
are an indication of changes in the size of the total herd. (4) Its 
fluctuations could, under a perfected method of rapid field estimates, 
be a guide to the management in planning commercial sealing operations. 
Six different estimates of the numbers of pups born on the 
Pribilof Islands in the years 1947 through 1951 are presented below. 
These estimates, based on a variety of data and methods, differ, but 
are all of a similar order of magnitude. The most objective estimates 
are those based on tagged seals, ages 3 and 4, recovered in the 
commercial kill. Because it is believed that tag-recovery estimates 
are the most reliable, they are given the most weight in arriving at 
a mean value for number of pups born and are also used in estimating 
certain mortality rates in the herd. 
For the purpose of this study the sex ratio among pups is 
considered to be 1:1. Among 1,172 fetal seals taken at sea, mostly 
during April and May, the percentage of males was 52.7 and of females 
47.3 (International Fur Seal Investigation, 1954, MS). The sex ratio 
among 1,000 living pups on 4 August 1950 was 50.5 percent males and 
49.5 percent females. 
The increase of pups from 1912, when the Treaty of 1911 took 
effect, to 1924, when pup counting was discontinued as impractical, 
is shown in table &. 
Size of the pup class in 1947 as derived from tag recoveries 
in 1950 and 1951. 
In 1947, metal tags marked in the "A" series were placed on the 
left front flippers of 19,183 seal pups of both sexes (fig. 8). Also, 
a quarter-inch hole was punched in the web of the left hind flipper 
between the first and second digits. In 1948, metal tags of the "B" 
series were placed on the left front flipper of 19,532 seal pups of both 
sexes. The primary objective of the marking program was the recovery 
of tagged seals at age 3 and 4 in the commercial kill, to permit calcu- 
lations of the size of the pup crop in the year of tagging. Other objectives 
were information on mortality rates, migration, homing instinct, and gro th. 
Tag-and-sample method.--The procedure of tagging animals and 
subsequently sampling them to obtain a population estimate has been. 
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