J 



70 



THE FUR SEALS OF THE PRIBILOK ISLANDS. 



MORTALITY AMONG THE SEALS.' 



On the rookeries but a slight mortality occurs among the adult seals. A few of 

 the cows are killed in various ways, chiefly in the struggles of the bulls for their 

 possession. A total of 131 of these dead cows was found on the rookeries of the 

 two islands last year. A score or more of bulls were found dead at the same time, 

 evidently as a result of contests with one another. But this loss in a herd of 

 nearly 100,000 adult animals is insignificant. 



DEATH OF PUPS. 



Among the pups the mortality is more striking. The average fur-seal pup after 

 it is a few weeks old is not an easy animal to kill or injure. In our experience we 

 have seen them stand hard knocks and even come trom under the feet of the bulls 

 uninjured. We have seen them tumble off and go bounding down the cliff's like 

 rubber balls without apparent injury. But when the little pup is only a few days old 

 it is a very different matter. In the rushes of the clumsy bull in his efforts to defend 

 or discipline his harem a certain number of the little fellows are crushed to death 

 before they are old enough to get away and pod by themselves. 



THE PARASITE UNCINARIA. 



In our investigations of the subject of mortality among the pups in 1S96, which 

 were begun late, we assumed that the chief cause of death among the 11,000 pups 

 counted before the middle of August was the trampling of the fighting bulls. The 

 more tliorough investigations of 1897, however, prove this an error. The principal 

 cause of death was found to be a small parasitic worm of the genus Uncinaria, which 

 infests sandy areas where the seals are crowded and tlie ground has become filthy. 



The embryos of the worm are taken in from the fur of the mother by the nursiug 

 pup and develop in the intestines, sucking the blood and causing the pup to die of 

 autemia. It is an infantile disease, and those which do not die before the middle of 

 August outgrow it and survive. After that time the.se natural or accidental causes 

 of death have but little effect ou the pups, though, as we shall see later ou, another 

 and more serious cause of death presently begins, namely, the starvation of the young 

 due to the loss of the mother at sea. For this man is solely resjjousible. 



THE COUNT OF EARLY DEAD PUPS IN 1890. 



This early mortality among the pups was made the object of a carelul enumera- 

 tion in 1890. A full record of the count by rookeries will be found in the statistical 

 appendix to this report. The following counts of the ''death traps" where the injury 

 of the worm was greatest will give some idea of its destructive effects : 



Jiecoril of j)it2>s, 18%. 



Rookery. 



Tolstoi (main, iucluding sand flat) 



Zapadni 



Reef 



Gorbatcli 



-o 1 i Pups dead 



^"P« '"'"'■ (August). 



n, 775 



17,648 



15, 258 



9,142 



1,495 



3,095 

 950 

 712 



' This subject is more fiillj' treated in a sperial paper li\ Ml'. Liica.s in Part III. 



