
disease. A few pups die of starvation when their mothers fail to return 
from a foraging expedition at sea, or when they do return, fail to find 
their young. Contrary to popular belief, few pups die as a result of 
trampling by adults. 
The greatest natural die-off takes place among the pups when 
they are a few weeks old. In order to study the day-by-day rate of 
mortality a study area was selected on St. Paul Island in 1951. Before 
the arrival of seals, a 15,000-square-foot plot, bounded by painted rocks 
and bisected by an elevated walkway, was laid out on Vostochni rookery. 
With the first pup born a systematic survey of the area was begun, and 
the accumulated carcasses were counted at 5-day intervals throughout the 
season (table 13). 
Estimate of the number of pups born annually, from the trend of the 
en =: Soe 
‘commercial harvest 


As noted earlier, the commercial harvest in a given year is a 
direct product of the pup recruitment of 3 and 4 years earlier and, to a 
very minor extent, of 2 and 5 years earlier. Under a uniform system of 
harvesting, the number of seals killed should bear a fairly constant 
relation to the size of the pup class. Observing that the commercial 
kill has shown an increase over the past 28 years, (1923-51), the writers 
have attempted to draw a parallel in the increase of the annual birth rate 
of pups. A smooth curve has been fitted to the increese in kill (table 6). 
The mean kill in a present-day reference period (1947-51) is 1.5807 times 
the mean kill in an earlier reference period (1928-32). Therefore, the 
size of the pup class today is estimated to be 528,036 (that is, mean 
count of pups 1928-32, or 334,052, times 1.5807). But the mortelity rate 
is higher today than it was in 1928-32, from direct evidence of carcass 
counts (table 11). Thus, the percentage of pups that live to killable 
age is now less than it was. On the basis of 2 to 3 percent mortality 
during the reference period and 12 to 17 percent during the modern period 
(table 11), there has been roughly a 10-percent increase in mortality. 
Applying this correction, the mean birth rate becomes approximately 
590,000. 
The reference period 1928-32 has been selected for three 
reasons. First, the size and growth rate of the pup class then had been 
fairly well established through actual counts between 1912 and 1924. 
Second, the annual kills were about as predicted, indicating that compu- 
tations of herd size were correct. Third, after the closed season of 
1912-17, when the only seals killed were those taken for food, commercial 
harvesting was resumed. By the time of the reference period the effects 
of the sealing holiday would have been reduced to negligible proportions. 
Estimate of the number of pups born annually, from the trend 
of the harem—-bull count 


Assuming, egain, a uniform system of harvesting, and its corollary, 
a uniform system of sparing male breeders, the number of harem bulls should 
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