110 ALASKA FISHERIES AND FUR INDUSTRIES IN 1919. 



Increase or Decrease in Number of Pups in 1919 from 1918. 



A casual inspection of the foregoing table discloses a great varia- 

 tion in the growth of the various rookeries. It ranges from a loss of 

 19.31 per cent in one case to a gain of 45.20 per cent in another. 

 Some of this variation might be attributed to the defects in the 

 method of arriving at the number of pups on rookeries not actually 

 counted, but it can not explain it all. A constant rate of increase 

 simply is not a phase of rookery development, and this is the greatest 

 objection to the use of a single breeding area as a type in census cal- 

 culations. 



COWS. 



NUMBER. 



The number of breeding cows is by inference the same as the num- 

 ber of pups, since but a single young is born annually. Although a 

 birth of twins is unknown in the species, it is not believed to be entirely 

 impossible from an anatomical standpoint and may on very rare 

 occasions occur. 



The figures for the pups show that there has been an increase of 

 cows of 9.97 per cent from 1918. This figure is to be compared with 

 11.63 per cent for 1918. 



The figures show that the average annual increase is between 9 

 and 10 per cent under present conditions. This is an exceedingly 

 slow rate of growth for animals which live as long and breed as often 

 as fur seals. It emphasizes the enormous loss the species suffers 

 annually from some enemy of which we know jjractically nothing. 

 It now seems certain that 50 per cent of all animals born are lost 



