23 



KNUT DAHL 



In this diagram llie four vertical lines denote the four dates of the investigation. 



The unbroken curve denotes the average number of cod larvae per 5 min. tow-nettings 



at 1 ni. depth and 350 metres 



length, calculated by integration Sapdr>oe»,|jorci Söndeiadfjord. 



of the figures gained by the ~" 



20 townettings , which were 



made on eacii occasion at 



the four stations in the tjord. 



The broken curve shows the 



alterations in salinity at 20m. 



depth in the middle station. 



The dotted curve denotes 



the distance under the 

 surface, where on the same 

 station, the absolute specific 

 gravity of the water' was 



1-021, a value the importance 

 of which has previously been 

 mentioned. 



If we study this diagram 

 we shall observe that the 

 decrease in the number of 

 larvae closely follows the 

 upheaval of the salt water 

 and the rise of the isopykn 

 of 1-021 towards the surface, 

 expelling the "fry water" of 

 lower salinity. When the 

 salinity again was lowered 

 and the isopykn of 1-021 

 again subsided the number 

 of larvae rose. 



Similar phenomena were 

 observed also in the Sandnes 

 Fjord, and the circulation in 

 this fjord being quicker, the 

 alterations in the numbers 

 of fry were here still greater. 

 Also a study of the occur- Fig. 8. Diagrams showing hydrographical changes in the Sandnes and 

 rence of the Pleuronectid Sondeled Fjords, spring, 1905. 



larvae shows exactly the 



same great decrease in their number parallel to the expulsion of the upper water- 

 layer in which they lived. 



The following diagrams will illustrate this (Figs. 10 and 11). 

 • The weight of the water in gr. pr. ccm. 



t.ao-t.iio-zolÈ-'^àb-ioïfc. 



Isopykn i-031 



