106 THE FUR SEALS OF THE PRIBILOF ISLANDS. 
It is evident that between these two seasons the decrease in the herd was more 
strongly marked than between any other two seasons. The reason for this is of 
course plain and will be referred to again in its appropriate connection. In a word, 
the resumption of pelagic sealing in 1894, nearly doubling as it did the draft of the 
preceding year on the herd, naturally showed itself very strongly on the rookeries 
in 1895. , 
PHOTOGRAPHS OF ABANDONED TERRITORY. 
There is one way in which the photographs of successive seasons show definite 
results, and this is in the recording of the absolute abandonment of breeding ground. 
Thus on the flat at the head of the “slide” on Ardiguen rookery there were 78 cows 
in the season of 1596 and none whatever in 1897. This fact is clearly recorded in the 
photographs of the two seasons. Photographs of the large breeding masses on Reef 
rookery, Tolstoi, and Vostochni, which are calculated to show most plainly the effects 
of shrinkage, give clear evidence of the fact even between two successive seasons. 
This evidence might not, however, in view of the daily fluctuations in rookery popula- 
tion, be so clear if it were not corroborated by more definite proof. 
THEIR LIMITATIONS. 
There are, on the whole, many reasons why photographs are at best unsatisfactory 
guides to the actual condition of the rookeries from year to year. In the first place, it 
is difficult to take them on exactly the same dates on account of adverse weather 
conditions, and to be of value for comparison between two successive seasons they 
should be so taken. Again, the period during which photographs of any value can be 
taken is short. It falls within a few days before or after the 15th of July, which was 
found in the season of 1897 to be the maximum date of rookery population. But 
between this maximum and the population of the 8th of July there had been an 
increase of 20 per cent, while on the other hand from the maximum of the 20th of the 
same month there was a decline in population of 38 per cent. 
THEIR RELATION TO THE DAILY COUNTS. 
To take a concrete example: The population of the Amphitheater of Kitovi, as 
counted at its maximum on July 15, showed 703 breeding cows present. On the 14th 
its population was 536, a difference between the two days of 20 per cent. Photographs 
for these two days of this rookery in the breeding season of 1897 would have indicated 
20 per cent of difference, if they indicated anything. Suppose similar conditions for 
the year 1896, and that a photograph taken on the 14th of July in one year is to be 
compared with one taken on the same date of the next, or vice versa. Such a com- 
parison would clearly be misleading. The result would be more striking if the 
comparison was made between a photograph in one season for the 15th and one in 
another season for the 20th. If we continue the comparison we find that by the 31st 
of July our population of breeding cows has declined 46 per cent from its maximum. 
Here, however, comes in another element of confusion in the use of photographs. 
The pups have been growing in the meantime and are becoming more and more 
conspicuous. They are always at least twice as numerous as the cows, and in a 
distance photograph they can not be readily distinguished from their mothers. It 
therefore happens that a photograph taken on the 3lst of July for the Amphitheater 
