36 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



fore seems safe to say that,, in the case of the ^lackerels, the forma- 

 tion of dense schools is a necessity for the most successful fulfillment 

 of the reproductive process. 



These influences in determining the schooling instinct may, per- 

 haps, be more evident when they are considered in connection with 

 the migrations of the schools of these fishes, particularly in the 

 cases of the Common 'Mackerel and the Spanish ^Mackerel whose 

 migrations are, to some extent, definite and regular. While these 

 movements are influenced, to a great extent, by temperature and 

 other conditions, their fundamental causes are to be found in the 

 reproductive instinct and in the necessity of securing food. The 

 initial impulse which drives them from their winter home and starts 

 them on their spring migrations is probably given by the approach- 

 ing maturity of their reproductive organs ; the course which they 

 follow, although determined to some extent, perhaps, by tempera- 

 ture and the available food supply, has for its ultimate goal condi- 

 tions of water and temperature which are suitable for spawning. 

 On the other hand, the later movements of the schools, in the summer 

 and autumn after spawning has taken place, are doubtless regulated 

 partly by temperature, but chiefly by the movements of schools of 

 other fishes upon which they are feeding. 



To sum up briefly the habits of the fishes of the Mackerel family: 

 They feed exclusively, for the greater part of the year at any rate, 

 upon the free-swimming animals of the surface, and they spawn in 

 the open waters of the ocean; for the securing of food they are 

 necessarily of pelagic habits, and extremely active and predacious ; 

 for the securing of conditions suitable for spaw^ning, extensive move- 

 ments to favorable localities are necessary, and the formation of large 

 schools is essential for the most successful completion of the process. 

 These fishes are thus, to a high degree, predacious, pelagic, gregarious, 

 and migratory. 



Besides the similarity in their habits, the great degree of the 

 adaptation of the external features of their bodies to their active 

 and pelagic existence is ver}' characteristic of all the fishes of this 



