ALASKA FISHERY AND FUR-SEAL INDUSTRIES 



147 



number of dead pups. It is only reasonable to believe that the ratio 

 of dead pups to living pups will increase considerably as the rookeries 

 increase in size. An unfavorable cold wet season also causes a larger 

 percentage of dead pups. 



It w^ould be very desirable to make another complete pup count to 

 check up on figures which have been estimated for the past 15 years. 

 It is very probable that as the herd increases in size the rate of growth 

 will become smaller. Unless some sort of epidemic reduces the herd 

 at various intervals, a point will finally be reached where the size of 

 the herd will remain practically constant. This condition must be 

 reached sometime; otherwise seals, the same as any wild animals, 

 woidd increase to the point where their natural growth would be the 

 cause of their extermination. Some ^vild animals increase to a certain 

 point and then remain fairly constant in numbers; others increase to 

 a certain point and then are nearly exterminated by disease, parasites, 

 or food shortage. 



Insofar as known, there have been no natural causes of a reduction 

 in the rate of growth of the seal herd within the past few years. There 

 is no known condition which causes a shortage of food and, owing to 

 the immense expanse over which the seals feed, it is not believed that 

 there could be a food shortage. There have been, of late, no ravages 

 of uncinaria, wliich at one time was, and again may be, the cause of 

 losing thousands of pups. 



There are always a few seals infested wdth the mange or some fur- 

 or hair-eating parasite. Tliis year there seemed to be more females 

 than usual with hair and fur badly eaten. This condition has not, 

 however, at any time in the known history of the islands become of 

 any great importance. 



Distribution of pups on the Pribilof Islands, Aug. 10, 1937, and comparison with 



distribution in 1936 



