52 



still under the influence of the Channel Atlantic water. But those 

 of the east coast further north must receive the impulse for the 

 summer migration from the northern stream. 



Both plaice and dabs thus exhibit in the migrations of the 

 schools and of the mature a strong tendency to migrate in the 

 direction of their entrance into the North Sea, the movements of 

 the former bemg suggested by an annual change which presumably 

 is caused by the pulsations of the Atlantic water, and of the latter 

 by the ripening of the gonads. 



The migrations of the schools are of particular interest to 

 fishermen, and since the migratory habits have evidently originated 

 in association with the coming of the species from the Atlantic, and 

 are still more than probably profoimdly affected and controlled by 

 the pvilsations of the Atlantic water m the North Sea area, the varia- 

 tions m the stream will bring about not merely the occurrence but 

 the abundance and scarcity of seasons. 



Migrations in General. — So far as the North Sea is concerned 

 it may be taken as a law that the direction of the migrations of the 

 schools, and particularly that of the mature mdicate whether 

 they have entered by the north or by the Channel. It has already 

 been demonstrated that the relative numbers of the schools in 

 different areas of the summer feeding ground also allows of this 

 being determined. 



It is not necessary to attempt to give now an exhaustive list of 

 migrants, but examples of which there is evidence from marking 

 experiments or otherwise may be quoted. The sole has already 

 been mentioned. It is a late arrival from the south which the 

 North Sea owes to the Channel, and it is stiU confined to the southern 

 part of the North Sea. Turbot may have entered the Channel, 

 but those of Northumberland, and presumably all to the north 

 thereof, came from the north. The same is true evidently of brill. 

 The flounder also entered by the north. It is possible also that 

 further south a subsequent entry of flounders took place ; of that 

 we have yet no evidence. But the flounders of Northumberland 

 arrived from the north. It is interesting to recall in connexion 

 with the discussion attempted on page 50 that mature flounders 

 migrate from Northumberland mainly to St. Andrews and the 

 Forth, but have also reached to near Aberdeen. It will be found 

 from a consideration of the facts of distribution that the vast 



