
some of these assumptions may be seriously questioned, particu- 
larly the mortality rates noted in assumption 2 and the total of female 
seals over 10 years of age, in assumption 4. That the mortality rates 
up to age 3 are similar in males and females is reasonable, but there is 
no positive evidence supporting it. From pelagic samples taken off the 
American coast in the spring of 1952 (International Fur Seal Investigation, 
1954, MS), the mortality in the age bracket 4 to 10 is estimated to be 
7.8 percent. However, samples taken elsewhere (of Pribilof seals) indi- 
cate a lower mortality. In the 1952 pelagic sample the proportion of 
females over 10 years of age was 59 percent of those aged 4 to 10. To 
what extent these samples are random in age composition is not known. 
For example, the yearlings, the largest single age group, are poorly 
represented in the 1952 pelagic collection. Consequently it is difficult 
to assess what weight should be given to them. 
That there are some uncertainties in the life table for female 
seals is apparent. These may be due to sampling errors, since even the 
best of the checkpoints are based on estimates of varying degrees of 
accuracy. Furthermore, year-to-year fluctuations in the different com- 
ponents of the herd may cause complications. As additional data and 
observations accumulate, these difficulties will be resolved, and at the 
same time there will almost certainly be some modifications in the 
following estimated life table. 
On the basis of the life tables, the total Pribilof seal 
population is approximately 1,840,000. This is a maximum figure never 
actually attained, for many pups die soon after birth, and while pups 
are dying and others are being born the commercial kill of bachelors is 
in progress. After the sealing season and after hookworm mortality has 
taken its greatest toll, that is, by mid-August, about 1,700,000 seals 
are alive. Before the birth of pups begins in the following summer the 
herd population has dropped, through natural mortality, to about 
1,300,000. For an average all~year estimate it may be said that the 
size of the Pribilof fur seal herd is about 1-1/2 million seals. 
Estimate of the size of the herd from the 
trend of the commercial harvest 
As a check on the figure of 1-1/2 million derived from 
various counts in the period 1948-51, two estimates have been obtained 
from a study of trends in the growth of the seal herd since 1924. The 
first is based on the trend of the commercial harvest, the second on 
the trend of the harem-bull count (fig. 13). 

To estimate the size of the herd from the observed increase 
in kill of group-III males it has been necessary to make the following 
assumptions: 
Ves 

