26 



The obvious difference whicli the three ways of communication between 

 the Baltic aud the Kattegat show Avith regard to the youug of the cod, both for 

 the pelagic and especially the bottom-stages, is caused by the hydrographic 

 conditions. 



It has been shown p. 14 how these cause the pelagic fish eggs and young 

 to be carried from the intermediate parts of the Danish waters, partly out towards 

 the North Sea, partly in towards the true Baltic. This must be the reason, why 

 the Great Belt was quite empty of cod young in July, though in May the pelagic 

 stages were not so few in numbers, also why the bottom-stages were absent from 

 the Southern Kattegat, Great Belt aud the eastern part of the western Baltic, but 

 were present in the northern Kattegat and true Baltic. 



The abundauce of the bottom-stages in the western part of the western 

 Baltic is also explicable in the same way. In the deep region west and south of 

 Ærø the cod eggs Hoat in the salt, resting water-layers at the bottom (see p. 12). 

 The eggs hatcli out there and the young develop without being carried away. 

 Only the young which rise to the surface during development are caught and 

 carried off by the surface-curreut. 



In order to foUow the growtli of the cod young, we have measured all 

 we took in 1904. The measurements are given in Tab. D (p. 30) in somewhat 

 summarised form, all those takeu in the course of one month in each region being 

 brought together. All cod up to 20 cm. are included in the lists, in which the 

 limit between the O and I groups stands out clearly the whole year through. 



The first cod young taken in 1904 were caught in February; but most of 

 them were under 1 cm. eveu in May. lu June, at the period when they were 

 going over to the bottom-stage, the cod young began to grow quickly. The growth 

 is somewhat dependent on the regional conditions, as appears clearly from Tab. D 

 when we compare the Little Belt with the western Baltic. In June the pelagic 

 young and the bottom-stages were taken in both regions; but both classes of young 

 were largest in the Little Belt, where at an earlier date there were relatively fewer 

 of the bottom-stages tlian in the western Baltic. The investigations were carried 

 out almost at the same time, viz. 13th aud 14th of June. The difference is even 

 more marked in August. In that month we took cod young of the 0-group of 

 8 — 12 cm., most at 9 cm., in the Little Belt amongst the plant-vegetation in 

 shallow water; in the western Bal tic, on similar ground, we found the cod j'oung 

 to be from 5—9 cm., most at 6 cm. There is thus a great ditterence in the size 

 of the cod young in August even in waters situated so near to one another as 

 the Little Belt and the western Baltic. The difference holds good, however, not 

 only for the young from different waters but also for those from differeut localities 

 of the same region. It is always found that the young taken in shallow water 

 on algal covered ground are larger than those taken at the same time on clear 

 ground in deep water. I have made this difference conspicuous in Tab. D by 

 placing the August hauls in the western Baltic in two lists, one for the algal 

 covered ground and one for the clear ground. The young taken on clear ground 

 of 18 — 20 fm. are 4 — 7 cm. in length, the majority 5 cm., whilst those from the 

 algal ground, as already mentioned, are 5 — 9 cm., the majority G cm. Tlie cod 



