REPORT OF COMMISSIONERS OF INLAND FISHERIES. 35 



form vast schools, in some cases of many square miles in area and 

 containing an immense number of fishes. The fishes of the same 

 school are usually of nearly uniform size and apparently do not 

 tend to mingle with other schools which may be in their immediate 

 neighborhood. Of the manner in which the fishes keep together in 

 the schools, very little is known. Observations on some fishes seem 

 to indicate that they keep together by sight. But however this may 

 be, it is possible, in the case of the Mackerels, to indicate certain 

 factors wliich are doubtless of influence in determining the instinct 

 which leads to the formation of the schools. One factor may be 

 their habit of feeding on other fishes which form large schools, for 

 instance, the herring, menhaden, anchovies, etc. In the vast areas 

 of the ocean, fishes of solitary habits are doubtless widely scattered 

 and of such uncertain occurrence that the compact masses of 

 such fishes as form large schools are the most available food supply 

 for fishes of such fierce and voracious feeding habits as the [Mackerels. 

 These conditions probably favor the massing together of a large 

 number of the Mackerel for the purpose of feeding. That the 

 individual fishes of a school may co-operate in " running down " other 

 fishes is not improbable, as this is said to be an observed fact in the 

 case of the bluefish which has similar habits as the fishes of the 

 Mackerel family. 



But a stronger influence in determining their gregarious habits is 

 probably to be found in the conditions required by the spawning 

 process. The successful accomplishment of reproduction in the case 

 of such fishes as the mackerel, herring, and the cod, where the sexual 

 products are shed out free into the water, demands the aggregation 

 of an immense number of fishes. If they did not breed together in 

 large schools it is obvious that the spawn and milt would become so 

 scattered by the movements of currents and tides that the chances 

 of the eggs becoming fertilized in sufficient numbers would be ex- 

 ceedingly small. It is also true that the greater the number of 

 spawning fishes massed together in a given area, the greater will be 

 the proportion of eggs which can be successfully fertilized. It there- 



