THE EQUILIBRIUM THEORY. 157 
‘THE EQUILIBRIUM A THEORETICAL FACT. 
There is, however, a certain amount of truth in this idea of equilibrium, and we 
may inquire what it is and what will be the condition of the herd and of the industry 
of pelagic sealing when it is reached. 
As already indicated, the condition of the fur-seal herd is determined by the 
relation of its various losses to its single source of gain, the yearly accession of young 
3-year-old breeders. From the history of the herd in the period from 1871 to 1880 
we know that the various losses which the herd suffered about balanced its gain, and 
there was neither increase nor diminution. From the nature of the losses which the 
herd is subject, to we may infer that in its less crowded condition within the past 
few years, they have been somewhat mitigated. This would be especially true of the 
loss through the parasitic worm and through fights and struggles on the breeding 
grounds. Under normal conditions in its present state, the herd might be expected 
to increase by a slight margin each year. That it does not so increase is due to 
the action of pelagic sealing. The measure of this possible increase in the herd is 
the margin of difference between the number of 3-year-old females which enter the 
breeding grounds in any season and the total number of deaths resulting to the adult 
breeding herd from old age and the incidents of the sea. 
DEATH FROM OLD AGE. 
If we assume for the breeding female an average life of thirteen years, this 
would give a breeding life of ten years, and the death rate from old age must each 
year amount to about 10 per cent of the breeding herd. On the other hand, it is 
clear from the proportion between the breeding herd of 130,000 and the quota of 
20,000 for the present year that the proportion of pups which survive from any birth 
rate to the age of 3 years is about one-third to one-fourth of the total number. The 
quota of the present time is therefore roughly a measure of the gain of the herd, as 
an approximately equal number of young females must survive. 
A HYPOTHETICAL CASE. 
As an illustration, let us assume for any given year a total breeding herd of 
180,000 cows. Of these 150,000 would be adults and 30,000 young cows coming into 
the herd for the first time as breeders and representing the normal gain of the herd. 
Assuming that, as a result of storms at sea, old age, and attacks of enemies, 10 per 
cent of the herd are lost in the winter migration, this would mean the absence of 
18,000 animals for the succeeding season, to cover which and provide for continued 
increase the herd receives a gain of 30,000 young animals. The net gain to the herd 
is, therefore, 12,000 breeding females. This is a liberal estimate of gain. 
THE POSSIBLE ABSTRACTION OF FEMALES. 
If the killing of female seals produced only the direct loss entailed by their 
absence, this removal of 12,000 females from the hypothetical stock of 180,000 
breeders would leave the herd in a state of equilibrium. But for each life thus lost 
results the death of an unborn pup, and with such part of the 12,000 females as are 
taken in Bering Sea nursing pups die also. This secondary loss is felt later in a 
