
INTRODUCTION 
The breeding colonies of fur seals Von the Pribilof Islands 
were discovered in 1786 and 1787 by Gerassim Pribilof, Russian navigator 
and fur trader. The herd at the time of discovery was estimated to con- 
tain 2,500,000 sesls (Sims, 1906, p. 38). In the next 150 years the 
seals went through alternate periods of intensive exploitation, when 
their numbers were reduced, and periods of rest, when they were allowed 
to recover (appendix A). In 1911, when the United States Government 
took over direct administration of the sealing industry, the seal popu- 
lation had reached an all-time low of about 215,000 animals. Under 
careful management, backed by the Treaty of 1911 which prohibited pelagic 
(open-ocean) sealing in the North Pacific, the seal herd recovered rapidly 
and at the same time returned a profit to the Government. 
With renewed growth of the population, the problem of taking 
a census grew increasingly difficult. The earliest estimates were little 
more than field guesses. Later, when the herd was at low ebb, maps were 
drawn and field counts were made with considerable care. Noteble among 
the early investigators were Bryant, Elliott, members of the Jordan 
Commission, Hanna, Clark, Osgood, Preble, and Parker (see Literature 
Cited). As a result of their work, a system of computing annually the 
size and growth rate of the seal herd was established in 1922. This 
system used as its point of departure field counts of pups and harem bulls 
as well as counts of bachelors in terms of the numbers killed. In the 
years that followed, 1923-48, the count of pups was abandoned, and popu- 
lation computations were based largely on earlier counts without 
renewed evidence of the size of the two most important herd elements, 
pups and breeding cows. For 10 or 12 years the management was able under 
this system to predict quite accurately each season's commercial take of 
seals. Beginning in the late 1930's, the take began to fall each year 
progressively below expectations. Simultaneously, the computed size of 
the average harem began to show an increase, from about 42 cows in 1935 
to about 94 in 1947. This increase (on paper) developed through use of 
a system wherein the number of cows and pups was computed annually along 
a straight line of increase, with little regard for observations that the 
kill and the count of harem bulls failed to increase in a similar way. 
It was not realized that the growth trend of the herd was following a 
sigmoid curve, rather than a rectilinear one, and consequently was 
flattening out as it approached its natural ceiling. By 1940 it became 
obvious that the old system of computation was no longer applicable—-that 
the herd was approaching its population limit, a limit imposed by the 
natural, as well as artificial, factors of life and death. Published 
computations of the size of the herd based on the old extrapolation pro- 
cedure are shown in table 1. 
1/ Callorhinus ursinus Linnaeus, 1786 
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