HOEK— INTRODUCTORY — XII — 



youngest bottom-stages there. From the end of the first year, the young plaice 

 migrate gradually and regularly, as they grow larger and older, further out to sea 

 into ever increasing depths. 



It is shown, that the biological character of the flounder is similar to that 

 of the plaice, but it is more a coastal fish and passes the first year of its life on 

 the bottom mostly in brackish water and in rivers. 



The picture presented by the dab is essentially different from that of the 

 plaice; it appears to be distinctly a stationary (localised) fish, as the eggs , larvae 

 and all the age-groups are distributed evenly and beside one another over a 

 wide area. 



The long-rough dab appears as a flat-fish which is limited in its occur- 

 rence almost entirely to the northern North Sea. It gives the impression of a 

 stationary fish whose biological character is similar to that of the dab. 



The biological picture, which the c o d in the German Bight offers, is strikingly 

 similar to that of the dab; the cod appears here as a stationary fish, all develop- 

 mental stages of which, from the egg onwards to the spawning fish, are passed 

 within the same region. Thus, all stages are found intermingled together at the 

 most different places, without any appearance anywhere or at any time of a ladder- 

 like distribution according to age and depth. 



Only the larger and older individuals seem to undertake any migrations worth 

 mentioning; for example, in the south-eastern parts of the North Sea, they keep 

 more to the open sea during the summer, but in winter — for the purpose of 

 spawning — they seek the shallower parts of the region. 



The biological picture given by the haddock is essentially different from that 

 of the cod; the haddock is distinctly a migratory fish. The earlier stages are 

 passed through on both sides of the loom. line and its migrations begin from the 

 third mostly the fourth year onwards; they then wander into the shallower regions 

 of the southern North Sea in order to seek out the feeding-places there. On the 

 approach of maturity, they return again in the course of the winter into the 

 northern North Sea in order to spawn. After the conclusion of spawning, migra- 

 tions to the feeding-places in the south again take place — and this to and fro 

 movement appears to be repeated regularly each year. 



On the other hand, the biological picture presented by the whiting is similar 

 in general to those of the dab and cod; it is a stationary fish, whose eggs, larvse 

 and adult forms of all ages, occur at the same spots and beside one another every- 

 where within the region investigated^ 



A considerable number of discoveries have also been recorded by the Heligo- 

 land naturalists regarding other food-fishes — their elaboration, however, has not 

 yet been completed. 



From what has been said above, and better still, from the reports themselves, 

 which appear here as Appendixes E, F and G, it is undoubtedly clear, that the 

 investigations carried out so far on several species have also the greatest import- 

 ance for the solution of general problems, and that the international investigations 

 have made good progress in this field. 



