FUR-SEAL CENSUS, PEIBILOF ISLANDS, 1917. 119 



In addition to the known loss which the herd of bachelors suffers 

 at the hands of man there is in constant operation the great factor 

 of natural mortality while the animals are away from the islands on 

 their migrations. With cows this loss has been found to amount 

 approximately to 50 per cent of all females during the first three 

 years of their existence. No more reliable data are available to 

 apply to the males, hence this deduction has been made. It is 

 divided arbitrarily into 35 per cent the first year, 20 per cent the 

 second, and 4 per cent the third. In this it is assumed both sexes 

 are born in equal numbers. 



There is natural mortality after the third year, but there are no 

 means of knowing exactly or even with any approximation what it is 

 but it must be a small percentage. It is believed allowances other- 

 wise made are ample to more than offset it, hence no deductions 

 have been made after the third year until the seals mature. 



YEARLINGS. 



The number of yearlings in the herd at the present time is ascer- 

 tained from the number of pups born in 1916. This was 116,977. 

 When the arbitrary number 40,941 based upon the assumption that 

 the loss the first year is 35 per cent, is deduct^ed there are left 76,036 

 to represent the males and females of this age in 1917. Half of these, 

 or 38,018, should be of each sex, and this number is the best available 

 for the females in 1917. Five males were killed as shown in the table 

 on page 118, thus leaving 38,013. It seems an insignificant matter to 

 deal with such small numbers when such large assumptions are in- 

 volved, but it is believed that the more known factors which can be 

 brought to bear in a problem dealing with unknown quantities the 

 better the result will be. (It should be remembered by any person 

 studying census computations that whereas exact figures are given 

 whenever the calculations involved lead to them it is in reality in- 

 tended that only the round numbers shall apply. The best which 

 can be made is a careful estimate.) 



There is little which can be added to the small amount of informa- 

 tion already available about this group of seals. A male, however, 

 was accidentally killed on St. Paul Island, August 10, 1917. Real- 

 izing the paucity of knowledge of the class, it was carefully measured 

 and weighed and the skeleton was entirely preserved. Its importance 

 seems to warrant a special study which has not been completed. It 

 can be stated, however, that the animal was very fat, weighed 38 

 pounds and was 36 inches long. Its skin, removed in the usual com- 

 mercial manner, weighed 7 pounds. 



No difficulty need be experienced by anyone in recognizing the 

 yearlings on the killing field or on the rookeries when it is remembered 

 that the animals are no larger, and in most cases smaller, than the 

 pups. But unlike the pups they have light gray throats and the 

 older animals' coloration otherwise in most cases. Their heads have 

 a puppish aspect, and like many animals the flippers (feet) grow large 

 before the rest of the bod}^ The lower canines are but little over half 

 as large as those of the 2-year-olds. 



