6o BULLETIN OF THE BUREAU OF FISHERIES. 



b\- any temporary condition of the animal causing it to be fat or lean, but is mainly 

 dependent upon the length of the vertebral column, which varies only within very 

 narrow limits. As shown beyond, especially under the discussion of 3-year-olds, the 

 use of this measurement makes it possible to classify bachelor seals with a high degree 

 of accuracy. 



THE YEARUNGS. 



Definition. — A yearling seal has been defined as an animal which has attained its 

 second summer, or one which has completed its first migration. The great majority of 

 the pups are boni in July, but some are born as early as the middle of June and a very 

 few as late as the middle of August. The seals of any one generation, therefore, can 

 vary in actual age but little more than 8 weeks, and for all practical purposes this 

 variation may be disregarded. Seals found on the islands the 3'ear following that of 

 their birth are and in fact must in practice be regarded as yearlings during the whole 

 of that year or from the time they arrive at the islands on the return from their first 

 migration until they leave to begin their second journey. The same principle applies 

 to the other classes of young seals, each simply representing one generatian in the 

 herd. It is true that a provision of the law of 1910, which fails to use the word year- 

 Ung, conditionally prohibits the killing of "any seal less than i year old." But this 

 prohibition is expressly stated to be subject to the "authority of the Secretary of 

 Commerce" and to the needs of the natives for food. Moreover, the subsequent law of 

 191 2 provides that male seals without restriction as to age may be kiUed as food for the 

 natives. Therefore it is a matter of no practical importance whether the actual age of 

 any given yearling be slightly more or slightly less than 12 months. 



It is, of course, impossible to determine the exact age of individual seals, but the 

 limited period in which births take place affords a means of approximation. Births 

 occur in greatest numbers from the loth to the 20th of July. After that date they 

 rapidly decrease, and although a few usually occur during the first week of August, 

 they represent the merest fraction of the total number. Births as late as August 10 

 are of very rare occurrence. Among the very few records of such cases which have 

 been found, one on August 14 and another on August 27 may be noted." In 1914 the 

 latest copulation recorded was on August 2 1 , the cow engaged being an old one and her 

 pup apparently but a few days old. It is evident, therefore, that j'earling seals found 

 in July may be slightly more or slightly less than 12 months of age, that those found 

 early in August are mostly more than that age, while of those found after August 10 the 

 chances are thousands to one that their age exceeds the exact year. 



Limited knowledge of yearlings. — During early obser\^ations of seals, it was natural 

 to expect that the yearlings, having but little sexual instinct and being but poorly 

 prepared to defend themselves in the rough-and-tumble of the hauling and breeding 

 grounds, would have little reason or desire to come to land early in the season. It was 

 also evident from the variation in the size of the pups in the fall and from the probable 

 vicissitudes of the first migration that yearlings would be likely to present a wider varia- 

 tion in size than seals of older classes. These conditions have been recognized by most 

 students of fur seals in the past and with some corroborative observations of the year- 

 lings themseh-es, it has generally been regarded as true that the yearlings come late to 



" Report Fur Seal Investigation, 1896-97, pt. 3, p. 43, 1899. 



