OF THE HABITS AND MIGRATIONS OF THE MACKEREL. 25 



certain bays, get the large spring fish two or three weeks earlier, whilst 

 the temperature is still low. 



In the south of Prance, where the migrations are essentially similar to 

 those which occur in America and on the Atlantic coasts of Europe, the 

 temperature of the surface water on the coast is never below 50° F. 

 (10° C), even in January, the temperature in February and March being 

 54° to 59° F. (12°-15° C.) [Marion.] 



From these facts it would seem that the large shoals first appear 

 in American waters when the temperature is 40°-45^ F. ; off the coast 

 of Ireland when it reaches 50° F., and on the Mediterranean coasts 

 when it approaches 60° F. We must, therefore, suppose either that 

 we are here dealing with three distinct races, which have become 

 adapted to different temperature conditions, in which case the species 

 must be capable of considerable variation in its habits in this respect, 

 or that the temperature influences the migrations of the fish indirectly 

 by determining the presence or absence of the particular organisms 

 which serve for its food in each locality. The latter explanation, 

 however, cannot be regarded as complete, since in some localities, 

 e.g., the jSTorth Sea, in autumn we have both herring and mackerel 

 present at the same time, yet whilst the mackerel retire to the south 

 the herring return to the north. 



The first approach of the mackerel to the coast in spring or early 

 summer is for the purposes of spawning, and the advantage to the 

 species of the young fish being hatched out near the shore, where 

 the smaller forms of pelagic organisms are present in abundance, 

 and the plankton is increased by the numerous larval forms of those 

 species which inhabit the coastal waters, is obvious. The presence 

 of the fish in the in-shore waters during the summer and autumn, on 

 the other hand, is to be explained by the fact that these waters are 

 at that time crowded with the young forms of other fishes, which serve 

 as a bountiful food supply to the mackerel. 



It has already been noted that when the fish first approach the coast 

 for spawning only the males can be captured with bait, the females 

 having ceased to feed at this time. Hence the first migration towards 

 the shore must be regarded as to some extent independent of the food 

 supply, and we may call it, with Sars, the " spawning migration." The 

 approach to the coast in the summer and autumn is, on the other hand, 

 a " feeding migration." 



What relation exists between the fish which take part in the two 

 migrations it is impossible to say. The autumn fish are said to be 

 smaller tlian those which come in the spring, and it has already 

 been mentioned that the fishermen maintain that they belong to a 

 different race. They are all uf ihem, however, immature, and cannot 



