PUR-SEAL CENSUS, PEIBILOP ISLANDS, 1917. 117 



exist to-day. The increase on any parti ular rookery is solely 

 dependent upon the number of cows coming there, and it is well 

 recognized that no law governs their hauling out. Thus, the percentage 

 of increase of pups (or cows) on almost all rookeries has been an 

 exceedingly erratic figure during the past six years. For the present, 

 therefore, this factor may be dismissed from census calculations as 

 having little value. In the preceding tables wherever the numb r of 

 pups r cows comes in it should be remembered that this figure was 

 computed from the average harem and these other methods of com- 

 putation were used only as a check. 



METHOD OF ESTIMATING BACHELORS. 



The bachelor seals 1 to 6 years old must be estimated, no count 

 worthy of serious consideration being possible. The most practica- 

 ble method of arriving at their numbers has been found to consist in 

 starting with the number of births of any one year and deducting 

 therefrom each year certain losses. 



The known losses are those killed on land in the regular proceeding 

 of the sealing industry. Thus, since the last census, August 10, 1916, 

 there have been killed on both islands 7,291 males over 1 year of age. 

 These 7,291 animals must be divided into their respective ages, 

 because killing is not and can not be confined to a single age, and 

 it would not be desirable if it could, because the trade calls for more 

 than one size and grade of skin. As a basis of the division into the 

 several ages there have been available some data on seals which 

 were branded when pups in 1912 through the initiative of George 

 A. Clark, of Stanford University. Some of these seals have been 

 killed each year and carefully measured in body lengths. A critical 

 study of these lengths discloses the fact that there is considerable 

 overlapping of every age in this character, so that a representative 

 mean of the typical seal of each age must be assumed. This has 

 been done wit \ great care. 



The results show that a seal makes its year's growth almost en- 

 tirely during the three months, August, September, and October; 

 that is, a 3-year-old in the fall of the year has a skin about as large 

 as a 4-year-old in the regular killing season. This fact should be 

 borne in mind if in the future killings arc limited to any particular 

 ages. Any limit of age which may be specified is given in order to 

 produce skins of a prescribed size, and these will not be produced if 

 the same age limits obtain in the fall as in the spring. For instance, 

 it has been customary during Government operation to order the 

 killings confined to 3-year-olcTs This meant that no skins smaller 

 than those furnished by the mean summer 3-year-old were desired. 

 Interpreted literally, then, all 2-year-olds in the fall were exempt even 

 though they had the proper size skins. The scheme was, of course, 

 faulty in this respect, that it prevented the killing of a size of animal 

 until it should have run the chances of surviving a winter when 

 death rates are very high. Of course the rational way to establish 

 a quota is to specify the lengths of animals to be taken and pay no 

 attention to age. Animals of known ages intergrade in every char- 

 acter known except osteological, so that ordinarily the age of a seal 

 can not be determined until after it has been killed. The same 

 objection applied to the limiting of killing to animals having skins of 

 a specified weight. The weight of the skin of any live seal can be no 



