Page:Popular Science Monthly Volume 54.djvu/681

1896 and 1897, and the same diminution to one third or one fifth of the former product may he assumed when we include also the results of the hunting at sea.

This proposition needs little comment. It is a simple deduction from the conditions of the preceding paragraph. The minimum estimate of former conditions is the lowest possible figure that could be in any way defended. The larger figure is apparently more nearly correct. The quota of 1898, of which we now have the record also, was about 18,000. It is not so stated in this paragraph, but the inference is inevitable that what is thus given as the decline of the “yield of the hauling grounds” is equally the decline of the breeding herd. A breeding herd which yielded without difficulty annually 100,000 killable animals (superfluous males of three years of age) must be reduced to something like one fifth its former size when it is able only with extreme difficulty to yield a quota of 20,000 such animals.

4. The death rate among young fur seals, especially among the pups, is very great. While the loss among the pups prior to their departure from the islands has been found in the past two years to approach twenty per cent of the whole number born, and though the rate of subsequent mortality is unknown, we may gather from the number which return each year that from one half to two thirds have perished before the age of three years—that is to say, the killable age for the males and the breeding age for the females.

The maximum and minimum figures here represent a division of opinion. The larger figure of two thirds would even seem to be a conservative estimate. The birth rate of 1897, as we know from close estimate, was approximately 130,000; it must have been greater in 1894, approaching 200,000. From this larger birth rate only about 20,000 males survived (the quota of 1897). There was doubtless a like number of females, the sexes being equal at birth and subject to like causes of natural loss. This gives a total of 40,000 in all, out of a birth rate of 200,000, which survived to the age of three years. This is one fifth, and it is evident that the mortality exceeds rather than falls below the maximum of two thirds.

5. The chief natural causes of death among pups, so far as known at present, are as follows, the importance of each being variable and more or less uncertain:

a. Ravages of the parasitic worm Uncinaria; most destructive on sandy breeding areas and during the period from July 15th to August 20th.

b. Trampling by fighting bulls or by moving bulls and cows, a source of loss greatest among young pups.

c. Starvation of pups strayed or separated from their mothers when very young, or whose mothers have died from natural causes.

d. Ravages of the great killer (Orca), known to be fatal to many of the young, and perhaps also to older seals.