— ii6 — 



The large haddock had their spring maximum in the deep, central part of the North Sea. 

 Both species, cod as well as haddock, spawn as is well-known in the spring months; 

 both have their characteristic spawning places and in both species the statistics confirm 

 the results obtained from the study of the distribution of the plankton eggs. The had- 

 dock eggs occur in great quantities in the deep, central part of the North Sea, and the 

 trawl hauls also show a spring maximum there. The cod eggs occur nearer to the coasts, 

 and here the statistical data also show a spring maximum for the catches of cod. 



These statistical investigations lead as in the case of the haddock to the acceptance 

 of two kinds of migrations, namely, 



1. a gradual migration out into deeper water as the cod reach the older, mature size 

 (see the distribution of the "cod" group in the northernmost part of the North Sea and 

 on the north coasts of the British Isles), 



2. a seasonal migration in spring towards the spawning places and one in summer 

 towards the deeper parts of the sea. 



It would naturally have been very desirable, if we could have been able to demon- 

 strate these migrations already by means of marking experiments, which have been 

 made indeed in the North Sea and on the coasts of Norway and Iceland. These experi- 

 ments however have everywhere encountered great difficulties in regard to methods. We 

 may refer here to Borley's paper, in which the different methods used are described. 

 The experiments at Norway and Iceland showed that the cod in the fjords undertake an 

 inward and an outward migration (see under "Norwegian Sea" regarding this). In the 

 North Sea 252 cod amongst others were marked and of these 42 were retaken, which in 

 itself is only a small number but yet a high percentage, almost a fourth of the fish set 

 free. The small sizes seem to have migrated but little and also to show but a small 

 tendency to seasonal migration. Of the larger fish, over 60 cm. in length, only 22 were 

 marked and one retaken, which had left the Dogger Bank where it was set free. Some 

 others, which had reached the size of 60 cm. after being set free, showed a tendency to 

 migrate towards the coast in the spring. 



The longest migrations amounted to about 70 nautical miles. The average monthly 

 growth in the 15 specimens which had been 3 months in the sea after being liberated 

 amounted to 1.5 cm. per month (summer months). 



We can see that these experiments embrace altogether too few specimens and present 

 too little variety in arrangement to permit us to draw definite conclusions. They must 

 therefore be looked upon as of use for orientating purposes in regard to methods. 



Norwegian Sea 



The Norwegian Sea shows so great a difference from the North Sea in regard to 

 the bottom conditions, depths and hydrography, that it is very difficult to compare them 

 with one another. It is worth while however to carry the comparison as far as possible. 

 We shall therefore make the attempt and first of all consider Iceland. 



It was shown in the second chapter of this report, that the cod spawn on the south 

 coast of Iceland in the early spring months, February, March and April, and somewhat 

 later, in April — June on the west coast. At that time enormous average catches, such 



