114 ALASKA FISHERIES AND FUR INDUSTRIES IN 1919. 



5,343 cows, an average of 28.88. The number of harems on the 

 entu-e island of St. Paul was less m 1919 than in 1918, but Polovina 

 increased by 7. This, together with field observations, indicates 

 that there was an excessive influx of bulls on this rookery, which 

 operated to prevent the average harem in 1919 becoming as much 

 larger than the general average as it otherwise would. In the light 

 of the knowletlge acquired on the migration of adult seals in 1919 

 it seems very plausible that the limited tlriving and killing from this 

 place would' tend to preserve here a larger excess than on rookeries 

 where commercial operations are more extensive. In other words, 

 the absence of driving and killing of males on a rookery hauling 

 ground seems in general to tend to preserve a surplus which in later 

 years floods the rookery. The same factor would be in operation at 

 Northeast Point, which was not driven during the closed season and 

 not fully driven in 1918. 



SIZES OF BULLS. 



The actual size of some adult bulls which appear in the early drives 

 of the season has been variously estimated. There is great variation 

 in animals full grown both in weight and length. The heaviest bull 

 weighed 604 pounds after being bled; many of them exceed 550. One 

 animal measured 87 inches from the tip oi the nose to the base of the 

 tail, and practically all that approached maturity exceeded 72 inches. 

 These results lead to the conclusion that the maximum size of early- 

 arrived full-grown rookery bulls is about 7^ feet in length and 700 

 pounds in weight. The average is about 6^ feet in length and 550 

 pounds in weight. It therefore seems clear that the 7-year-old ani- 

 mals of the 1912 branded series were not in 1919 nearly grown. It 

 now seems to be true that an animal able to hold a harem on a 

 crowded rookerv must be at least 10 years old. No 7-year-old was 

 noted in 1919 which would even come into the category of idle bulls. 



SURPLUS BULLS. 



The surplus-bull class is fast disappearing, and 1919 is probably the 

 last year it will be of sufficient importance to be considered. In addi- 

 tion to the old-age loss of 20 per cent which lias been allowed, it seems 

 altogether probable that 50 per cent has been lost through natural 

 causes. Oi course this has not all taken place in the one year, ])ut is 

 the cumulative loss, of an individual age class, for instance, from the 

 fourth to the seventh year. Heretofore there has been absolutely no 

 basis for the computation of such a loss ; it was considered to be small 

 and did not enter into the computations. After 1920 it is believed 

 information will be available which will enable the loss to be stated 

 fairly accurately for the third to the fourth years and less so subse- 

 quently ; possibly it will necessitate a revision of the losses arbitrarily 

 adopted below the third year. It will probably not materially change 

 the loss of 50 per cent the first three years, however, as each year's 

 work seems to indicate that this is very close to the actual condition. 



The assumption of five breeding years for the males does not seem 

 as yet to neecl revision. Certainly when bulls are abundant and there 

 is great strife on the breeding grounds an animal must be well devel- 

 oped and at least 8 to 10 years of age before he can hold a position, 



