
SUMMARY 
Twice since its discovery in 1786-87 the Pribilof fur-seal 
herd has been exploited to the verge of extermination, first under 
Russian and later under American ownership. Twice it has recovered. 
Under the present management system and within the framework of present 
environmental conditions the herd appears to have reached its popule- 
tion ceiling. At the same time, adjustments within the herd will continue 
to take place so that, for example, some of the smaller breeding units 
(rookeries) may continue to grow at the expense of the larger ones. 
The herd now fluctuates between a late-spring minimum of 1,300,000 seals 
and a summer maximum of 1,840,000. 
To obtain an approximation of the size of the fur-seal herd 
and its different age and sex classes, the authors have used the accumu- 
lated counts of harem bulls, the commercial sealing statistics, field 
counts and estimates of living and dead pups, returns at various ages 
of tagged and branded seals, ege and mortality data based on the recovery 
of tags and the reading of teeth for age, studies of reproductive success 
from seals taken on land and at sea, and aerial photographs of seal 
rookeries. 
The total size of the herd is estimated by three methods, of 
which the first listed below is considered the most reliable. All 
figures represent maximum-size estimates of the population, including 
the newborn-pup increment. 
From tag recoveries ---------+------- 1,840,000 
From the trend of the commercial harvest - - - ~ 1,670,000 
From the trend of the harem bull count - - - - - 1,550,000 
The average number of pups born annually in recent years as 
estimated by six methods is: 
From tag recoveries -------------+--- 530,000 
From rapid field estimates -------- 7" + — ~ 440,000 
From sample counts plus ground-area measurements 
from aerial photos -----------+--°- 580 ,000 
From sample counts plus harem-bull counts - ~ - - - 470 ,O00 
From the trend of the commercial harvest - ~ - ~ - 590 , 000 
From the trend of the harem-bull count ----- - 550,000 
Although the various estimates differ, all are of a similar 
order of magnitude, and it can be said with confidence that the approxi- 
mate number of fur seals in the Pribilof herd is a million and a half. 
The herd can be expected to fluctuate about its present mean size because 
of weather conditions, food supply, and mortality from hookworn. 
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