Difficulty in obtaining quota after 1887. For eighteen years after the Alaska purchase about one hundred thousand bachelor seals were Mistaking effect for cause. The percentage of seals of killable size was so small (fifteen to twenty percent) compared with the percentage of yearlings, that it is not surprising that the Treasury agents on the islands were impressed with the scarcity of young males, and being new men, inexperienced in matters relating to seal life, were easily led to mistake effect for cause and attributed the decrease to the killing of too many young males at the islands in previous years, instead of to the destruction of the mothers and young by The for cause. pelagic sealers, an error they were quick to cor- Mistaking effect rect after another year's experience. Decrease shown The number of seals killed each day during by daily killing. the killing season may be taken as a rough index to the rapidity of the decline of the rookeries in the past few years. Treasury Agent Charles J. Goff, in charge of the seal islands in 1889-'90, states in his official report that the average daily killing in 1890 was five hundred and twenty-two, while in 1889 it was one thousand nine hundred and seventy-four for the same period. ury Agent Goff. In his report for 1889 Treasury Agent Goff Report of Treasstates: "The alarming decrease in the daily, weekly, and monthly receipts of [skins by] the Alaska Commercial Company, and as a dernier resort by said Company to secure their one hundred thousand skins, the killing of smaller seals than was customary attest conclusively that . . . there is a scarcity of seals, and that within the last year or so they are from some cause decreasing far beyond the increase." He states further: "I regard it absolutely essential, for the future of the rookeries, that prompt action be taken by the Department for the suppression of illegal killing of seals in Bering Sea, and that the utmost economy be observed in taking the seals allowed by law." females was not noticed. Why decrease of A considerable decrease in the number of female seals upon the breeding rookeries might not be noticed at first where the total number is so large, but in two or three years the effect of this loss would be felt in the class of killable seals, and might there be quite evident. The loss in one class would thus follow surely but somewhat behind the other in time. When the diminution in the number of killable seals became notable, attention was at once drawn to the breeding rookeries, and it was found that they were being depleted. Thus Captain Webster deDiminished size clared: "The great destruction has been among females. Formerly there would be, on an average, thirty cows to one bull; now they will not average fifteen." of harems. Effect of decrease of females on male life. And Mr. Redpath (already quoted) stated: "Not more than one-half as many females are on the rookeries this year as were found there ten years ago." The reaction of a considerable reduction in the number of females upon the number of young male seals would be immediate and certain, while a reduction in males must reach such a point as to lessen the supply of bulls for the breeding rookeries before the birth-rate can be affected. There is no evidence to show that this limit has been reached in recent years, and it seems clear, therefore, that the reduction in numbers originated in and is to be attributed to the loss of Effect of de crease of females on male life. female seals. CAUSES. of seals should be If the above representation of the conditions of Where decrease seal life at the present time be accepted as correct, sought. the determination of causes is practically limited to the discovery of the origin of the increased mortality among female seals. It is our belief that the decadence of seal life Canse, pelagic on the Pribilof Islands is due to the destructive effects of pelagic sealing. sealing. opinion. As widely different opinions are held on this Reasons for point we will present at some length the principal reasons upon which our belief is founded. In the joint report of the Commission it is Decrease caused agreed that the diminution in the number of seals is to be attributed to the operations of man. As man comes in contact with the fur-seal in only two ways, that is, in pelagic sealing and sealing upon the islands, it follows that in one or the other or in both of these operations the injury must be inflicted. by man. of herd untouched by In order to enjoy a clearer view of the problem Condition it will be desirable to consider for a moment the man. conditions under which a herd of seals assumes its normal dimensions, uninfluenced by the pres ence of man. 2716- -44 Birth-rate and In the case of the seal or any other animal the death-rate. condition of the species as to number must always depend upon the relation of the birthrate to the deathrate. As long as these two are equal the number remains constant, provided, of course, the distribution of deaths among the various ages remains the same. Change the distribution, and there will be a temporary increase or decrease in the total number of the species, according as the deaths are shifted toward the later or earlier part of the animal's existence. Thus, suppose twenty years to be the normal age of the seal: if all deaths occur at the end of twenty years, the total number alive at any one time would be much greater than if the mortality was distributed throughout the whole period. When a certain distribution of this mortality is determined upon, however, the number of individuals living at one time will adjust itself to this distribution and will then remain constant, provided, always, that the distribution of mortality is such as not to affect the number of births. If, in any species, it could be determined that no deaths should occur until sometime after the reproductive age had been reached, such a species would increase with great rapidity. With equal certainty, if it were fixed that all deaths should occur before the reproductive age, the species would be shortly |