262 A HISTORY OF FISHES 



So much for the general distribution of marine fishes. 

 Ahhough a given species has a definite geographical range in 

 the sea, within the limits of this area individual shoals, or even 

 individual fishes themselves, are more or less constantly on the 

 move, and may undertake extensive journeys from one locality 

 to another. Such movements, or migrations, are rarely sporadic, 

 but generally occur with regularity at certain seasons of the 

 year. They are nearly always undertaken for one of two pur- 

 poses — reproduction or food — and are consequently known as 

 spawning or feeding migrations respectively. In the case of 

 the Tunny ( Thunnus) , for example, shoals of these gigantic fish 

 may make their appearance in a given locality, and after a 

 stay varying from a few weeks to several months, disappear for 

 the remainder of the year. The migrations of this species are 

 still imperfectly understood, but there is little doubt that they 

 are dependent on the movements of the shoals of Mackerel, 

 Pilchard, Herring, and other smaller fi.shes on which the Tunny 

 habitually preys. They enter the Mediterranean in huge 

 numbers in the earlier summer, and the fishermen, being 

 conversant with this habit, set special nets, sometimes miles in 

 length, that serve to intercept the fish and to guide them into a 

 very strong net, where they are surrounded, speared or clubbed, 

 loaded on to the boats, and finally landed to be cut up and 

 tinned. Mackerel {Scomber), which are essentially warm water 

 fish, keep to the open water during the winter, but in summer, 

 when the inshore waters become warmer, they approach the 

 coasts on both sides of the North Atlantic, and in our own 

 waters travel up the Channel into the North Sea. During May 

 and June they spawn close to the coast, and then move into the 

 bays and estuaries, drawn thither by the presence of shoals of 

 larval and young fishes. During this period the Mackerel can 

 be caught by means of seine-nets drawn on to the beach, but 

 from November to the following May none are to be found in 

 the North Sea. The Anchovy {Engraulis) is another species 

 passing up the Channel in the spring, but here the spawning 

 takes place in the outer part of the Zuyder Zee and in the 

 estuary of the River Schelde. The Pilchard [Sardina) approaches 

 the coast of Cornwall, the northernmost limit of its range, from 

 July to November or December, but always retires to warmer 

 regions on the approach of winter. It is of interest to note 

 that only the adults appear to travel so far north, and the young 

 or Sardines are never found in any abundance on the Cornish 

 coast. In this species the migration is entirely connected with 



