XI HOEK— INTRODUCTORY 



The plaice is taken in greatest quantities in the summer months over the 

 entire region of the North Sea. The reason for this, Prof. Henking is unable as 

 yet to conjecture. In the Kattegat, the greatest quantities are taken in the winter 

 months, whilst in the Skager Rak, a slight increase in the catch occurs in autumn. 



The gurnard is distinctly a summer fish in the southern North Sea, but just 

 as distinctly a winter fish in the Kattegat. 



The lemon -so le and witch are, in contrast to the plaice, marked summer 

 fishes in the Skager Rak, whilst the material for the North Sea is not sufficiently 

 representative to permit of anything definite being said. 



Sole, turbot and brill are similar: in the Skager Rak, they show a distinct 

 minimum in the summer months, and are therefore to be regarded as winter fish 

 there, whilst they occur more uniformly in the southern North Sea. 



The cod shows fluctuations in the quantities, which might lead to the belief 

 that migrations occur between the various parts of the sea; in the true summer 

 months, considerably fewer cod are taken in the southern North Sea than at other 

 times, at the same periods rich hauls are made in the Skager Rak. The Skager 

 Rak gives up some of its supply to the Kattegat, so that an increased fishery 

 takes place here in the first half of the following year. The Kattegat receives a 

 further increase from the north, however, like the southern North Sea, in the 

 months towards the end of the year. An increase in the quantities of the cod 

 thus occurs in the southern North Sea in the winter months. It cannot be said, 

 however, that the account given is the only possible explanation. 



The catches of the ling show a maximum in winter in the Skager Rak, and 

 somewhat later in the southern North Sea. In the Skager Rak, a second maximum 

 occurs in the middle of summer. 



Data are also given for the cat-fish, dab, green cod and pollack, and 

 the rays, but for these reference may be made to the paper itself. Prof. Henking 

 calls the picture given by the occurrence of the cod-fishes still a "varied kaleido- 

 scopic picture"; full clearness has not yet been obtained, we are still too near the 

 beginning of the investigations. 



With regard to the results of the investigations published by Prof. Heincke, Heinckc's results 

 only the conclusions are given which he has reached with respect to the mi- 

 grations of the food-fishes more closely studied. As to the methods used by 

 the Heligoland naturalists, only that of the age-determination by means of the 

 otolith rings, as applied to the flat-fishes and especially the plaice, and the results 

 attained by it, may be mentioned here. 



For the plaice of the German Bight, the experiments in setting out marked 

 fish have given some direct po,sitive results, which Prof. Heincke summarises 

 as follows: 



1. The great majority of all plaice marked are recaught in the same narrow 

 region in which they were set out. 



2. The plaice may in some cases migrate very quickly from one region to 

 another. 



The biology of the plaice in the eastern North Sea, offers the following picture. 

 The larvîe migrate into the warm, quite shallow water close to land, and pass the 



