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 takeu 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 takeu 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 bluefish in the beginning 
of the century may have had a similar cause; but the subject is an untilled 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 tilefish. 
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 
