ALASKA FISHERY AND FUR-SEAL INDUSTRIES, 1921. 83 



Average harem in 1921 for all fur-seal rookeries on Pribilof Islands — Continued. 



The average harem for the entire herd is 45.19. East ChfFs rookery 

 on St. George Island contained the largest average, with the exception 

 of Staraya Artil rookery, there being but 1 bull to every 60 cows. 

 Lagoon rookery on St. Paul Island had 1 bull to every 18 cows. 

 These extremes show how the topography of the rookery influences 

 the average harem. East Cliffs rookery is a narrow beach at the 

 base of a high steep cliff. One end is closed by a vertical wall of 

 rock at the water's edge. Expansion can only occur at the other 

 end of the rookery and there is room for idle bulls only at that place. 

 Lagoon rookery, on the other hand, has opportunity to expand 

 in all directions, and it is easy for the idle bulls to capture a few 

 cows. The bulls and harems can scatter all they please. 



LOSSES OF MALES. 



In the winter migrations of seals it has long been known that 

 the adult males remain farthest north. The young males go farther 

 south, and the females are found at the southern limits of migration. 

 The killer whale, probably the greatest known enemy of the seal, 

 is found around the Pribilof Islands, appearing in the spring at about 

 the same time as the seals do. Although there is no definite evidence 

 to support the supposition, it would not be impossible for these 

 killers to follow the seals south as far as the males go and prey prin- 

 cipally upon the younger males. 



The increase of 3-year-old seals has not kept pace with the increase 

 of cows. Sealskins taken in 1911, all or nearly all 3-year-olds, num- 

 bered 12,002. In 1920 there were 18,831 skins taken from this 

 class. This is an increase of 56.9 per cent. The estimated number 

 of cows was placed at 75,000 in 1911, a number not far from correct. 

 In 1920 there were 167,527 cows, an increase of 123.37 per cent. 



The 1920 census places the loss of seals during the first three 

 years at 35 per cent for the first year, 15 per cent for the second, and 

 10 per cent for the third. These figures are probably not far wrong 

 for the females. As the evidence seems to indicate a higher loss 

 for the males, the percentages for the first three years are provisionallv 

 placed at 40 per cent for the first, 17^ per cent for the second, and 

 12^ per cent for the third. The losses for the fourth and subsequent 



