54 REPORT Of commissioners of inland fisheries. 



they have some times been rare, and indeed there is some reason for 

 believing that, in the early history of the country, they were totally 

 absent for several years. These periods of scarcity have often been 

 erroneously attributed to overfishing, and this is the reason for the 

 useless restrictive legislation which has been intermittently applied 

 to the mackerel fisheries since as far back as Colonial times. 



The causes which bring about these fluctuations in the abundance 

 of the mackerel are very little understood at present on account of 

 the difficulty of direct observation on the conditions to which their 

 lives are subject. It is perhaps not entirely certain that the non- 

 appearance of the mackerel in a given locality signifies their absence 

 from that place; they may be present in the depths and refuse to 

 " show up " at the surface on account of some unusual conditions of 

 the food supply or for some other reason. It is probable, however, 

 that the apparent abundance or scarcity of the fish is real. Merely 

 local variations in numbers may be due to variations from year to 

 year in the course of their migrations, but a general abundance or 

 scarcity, throughout a large area, must of course be caused by a 

 variation in the total numbers of the mackerel. 



Variations in the course of their migration may perhaps be 

 induced by the presence or absence in particular localities of an 

 available food supply, or by the unusual number or occurrence of 

 enemies, or by some irregularity in temperature or other conditions 

 somewhere in their path which may turn them aside. On the other 

 hand, the extreme fluctuations of the actual numbers of the mackerel 

 is probably to be explained as the cumulative result through a 

 series of years of a succession of favorable or of unfavorable condi- 

 tions in the environment. 



The numbers of mackerel in existence at any particular time must 

 depend on the balance of the various external influences in the world 

 round about them; such influences, for example, as the water tem- 

 perature at the time of spawning and during the incubation of the 

 eggs, the direction and strength of currents which may affect the 

 fertilization of the eggs, the size and density of the schools of spawn- 



