70 THE FUR SEALS OF THE PRIBILOF 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 160,000 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 from under the feet of the bulls 
uninjured. We have seen them tumble off and go bounding down the cliffs 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 1896, 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 thorough 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 the ground has become filthy. 
The embryos of the worm are taken in from the fur of the mother by the nursing 
pup and develop in the intestines, sucking the blood and causing the pup to die of 
anemia. It is an infantile disease, and those which do not die before the middle of 
August outgrow it and survive. After that time these natural or accidental causes 
of death have but little effect on the pups, though, as we shall see later on, 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 responsible. 
THE COUNT OF EARLY DEAD PUPS IN 1896. 
This early mortality among the pups was made the object of a careful enumera- 
tion in 1896. 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: 
Record of pups, 1896. 
: Pups dead 
Rookery. Pups born. (August). 
Tolstoi (main, including sand flat) 11, 775 1, 495 
Papad ni ccesvecaasnsnascnaweneuraesiesveies vt 17, 648 3, 095 
ROG Ef oocecdcecisicerinsate siawerseinanac' crescents 15, 258 950 
Gorbateh ccssews vecsweweeeuseeracoemesstwavesnesownteoses 9, 142 712 
' This subject is more fully treated in a special paper by Mr. Lucas in Part 1II. 
