NATIONAL FISHERY CONGRESS. 355 



I. It has been contended from time to time, during periods of scarcity, that over- 

 fishing or the employment of particular apparatus or methods was to blame. That 

 this theory was advocated even as early as colonial times is evidenced by legislation 

 affecting the methods of taking mackerel which we find recorded in the colonial laws 

 of Massachusetts. With each succeeding period of wane this theory is revived, but 

 its advocates become silent with the advent of prosperity, when the very methods 

 complained of are plied with renewed vigor, or perhaps replaced by more effective 

 methods. The fact that there has been no continuous diminution in the quantity of 

 mackerel taken during the last eighty years, together with the fact of the regular 

 alternation of large and small catches having no casual connection with the employ- 

 ment of new methods, seems to sufficiently dispose of this theory as the sole or even 

 an important explanation. We may quote the weighty opinion of Dr. Goode. He 

 says of the mackerel: 



It seems quite evident that the periods of their scarcity and abundance have alternated with 

 each other without reference to overfishing or any other causes that we are prepared to understand. 



The area within which the mackerel is subject to man's influence is but a small 

 part of the vast expanse over which it roams, and the time but little more than half of 

 the year. To one who appreciates the magnitude of the struggle for existence which 

 rages in the ocean, the constant dangers and many natural enemies which beset the 

 mackerel at all times and during every period of its life, the numbers which fall to 

 man must seem but the merest trifle compared to the multitudes which are destroyed 

 by other causes. We may arrive at a reasonable estimate of how insignificant human 

 influence sometimes is by an examination into the history of man's conflicts with the 

 rabbits in Australia, the mongoose in Jamaica, the sparrow in our own country, the 

 locusts and other injurious insects everywhere, etc. On the other hand, there are the 

 cases of the bison, the fur-seal, the great auk, and many other birds and mammals, as 

 well as fresh- water and shore fishes, to bid us be cautious; and we may yet learn that 

 the small numbers (relatively to those which naturally succumb) of mackerel taken by 

 man may turn the balance in the direction of that fish's numerical decline. 



II. Infectious diseases may decimate the ranks of the mackerel hosts periodically. 

 This is a possible explanation for which there is absolutely no evidence. Fresh-water 

 and anadromous fishes have been known to be thus destroyed in vast numbers by 

 fungous and other diseases, and a great fatality among the blueflsh in the beginning 

 of the century may have had a similar cause; but the subject is an uutilled field with 

 regard to sea fishes. The mackerel is almost invariably affected by large numbers of 

 parasites, but these appear to produce no ill effects. No bacterial or other diseases 

 are known. That slight changes in the physical conditions of the sea may destroy 

 life on a stupendous scale is evident from such observed cases as that of the tiletisli. 

 If such destruction of the mackerel has taken place the fact has escaped notice. 



III. A third and perhaps more worthy suggestion would lead us to seek the 

 solution of the mystery in the effect of environmental influences on the fertility of the 

 species, the relative abundance during one season being the result of greater or less 

 fertility in previous seasons. Or, the actual fertility of the parent fish remaining the 

 same, the physical and other conditions may be such as to destroy the eggs and young 

 in greater or less numbers, resulting in subsequent times of scarcity or plenty. Though 

 there is no direct evidence of variable fertility in the case of the mackerel, many 

 analogous instances are known of seasons of greatly increased or diminished fertility in 

 other groups of animals, of which every observant naturalist has met with many. The 



