280 



BIOLOGY OF THE SEAS OF THE U.S.S.R, 



In Kiel Bay salinity was found to vary from 3-9 to 26-3% on the surface and 

 from 10-3 to 28-8% at a depth of 14 m. Moreover the change of salinity some- 

 times occurs very rapidly. 



The occasional mass penetration of a more saline-loving fauna into the 

 Baltic Sea is caused by the periodical inflow through the straits of masses of 

 more saline water from the North Sea. Thus in the spring of 1923 Schulz 

 reported that huge masses of saline water (more than 34% ) had flowed into 

 the Kattegat bringing great numbers of spawning haddock (Gadus aeglefinus). 

 The haddock larvae were brought by the bottom current into the southern 

 straits and the western part of the Baltic Sea. As a result, the usually low yield 



Fig. 123. Salinity range of the Danzig depression from 

 1902 to 1907 (Schulz). 



of haddock rose in 1925 to 50,000 kg, and in January and February 1926 to 

 500,000 kg, but the catch fell off sharply in March as the haddock migrated 

 back to the Skagerrak to spawn. 



Deep saline waters, penetrating periodically through the deep troughs into 

 the Bornholm depression, frequently form there a very complex system of 

 overlapping, accompanied by the usual phenomena of stagnation. The 

 highest salinity observed there was 18-93% , the lowest — 14-87% (September 

 1921), with an oxygen content of 0-7 per cent. However, at other times and at 

 precisely the same depths an oxygen content of 80 per cent has been recorded. 

 It has been noted that a layer of water of the same thickness as that over the 

 shallows situated to the west — approximately 40 m — is homohaline; in 

 winter it is also homothermic and is well mixed. 



The diagram of the Danzig depression in Fig. 123 is a clear illustration of 

 this. The deep waters of the Bornholm depression (105 m) may partly pene- 

 trate even farther into the deeper Gotland depression (249 m). The salinity 



