104 



inhabit the southern part of the Barents Sea. Up to 123 specimens of Bolinop- 

 sis per cubic metre were observed in July. This most predatory form destroys 

 a huge amount of various plankton organisms, mainly Calanus finmarchicus. 

 Experimental investigations have led to the conclusion that the mass of 

 Ctenophora observed requires about 170 mg/m 3 of food, and the annual pro- 

 duction of Ctenophora was, according to the 1950-54 data, 343 mg/m 3 . 



In the second half of June 1938 the total amount of plankton in the south- 

 western part of the Barents Sea was 1-5 million tons less than in 1939 and 

 1-1 million tons less than in 1937. Evidently such considerable fluctuations in 

 plankton development and, in particular, in that of Calanus and Ctenophora 

 would cause considerable fluctuations in the quantitative distribution of 

 herring and other plankton-eating fish. 



Previously, 1935 was an equally unfavourable year for the feeding of herring 

 and other plankton-eating fish. The distribution of herring in the Barents 

 Sea and the routes of their horizontal migration depend to a great extent on 

 the composition and distribution of plankton : in summer, herrings move to 

 the east with the mass of the growing plankton. Herring fattens up mainly 

 in the southwestern part of the Sea. By the end of the winter it moves in the 

 opposite direction. 



As has been shown also for the seas off North Europe, water bloom (Phaeo- 

 cystis, Rhizosolenia) either changes the migration routes of herring or makes 

 them sink to great depth, below the bloom zone. In spring and summer the 

 main mass of herring is in the upper layers of the sea, where it is intensively 

 fattened on red Calanus and Euphausiacea {Thysanoessa inermis). In spring 

 and autumn herring migrates vertically, together with the plankton (Fig. 

 40) : in winter it keeps to the depths. Masses of plankton, primarily Calanus 

 finmarchicus and Euphausiacea, migrate from the depths into the upper 

 layers in March and April. This rise is connected with breeding, which takes 

 place in the upper layers of the sea. Shoals of herring rise from the bottom 

 layers at the same time. 



The influence of herring, caplin and the fry of other fish which feed on 

 plankton, upon the latter, is very considerable. Manteufel (1941) gives the fol- 

 lowing approximate estimate: in 1934 about 200,000 tons of herring entered 

 one of the gubas of the western Murman Peninsula. In the course of a year 

 these herring must have eaten not less than 4 million tons of Calanus plankton. 

 If we assume that the shoal of herring which enters the guba forms only a 

 small part of the total amount of Barents Sea herring, and that about the same 

 amount of plankton is eaten by caplin and that the other plankton-eating 



