by itself has no harmful effect upon herring. There was a great deal of Phaeocystis in the surface 

 layer (to a depth of 25 m.)- Thiere was little zooplankton at 0-10 m. and there were almo.st no her- 

 ring. The best catches of herring were made in a layer from 10 to 20 m. There was as much 

 Phaeocystis there as at the surface, but there was 4 times as much zooplankton there; therefore, 

 the herring had sufficient food. 



JL 



400, 



100 >>. 200 ■ 30C ' 400 ! 



^ -^ "7' 3/ 



'mg/m^ 



•./ Phaeocystis 

 ^/Colanus iinimz- 

 ■2:Jhicus i-)hij 



/ Calaniis jinmazchicus 



, III- IV -V 



' Themislo a8ysso!um ju 



Colanus hypeeSoesus jir 

 Themislo adyssoeum jir 



Figure 14. Change in the amount of plankton and the temperature of the water in the zone 

 of the Phaeocystis "blooming" . 



In June-July, the diminishing Phaeocystis "blooming" is replaced by the production of dia- 



toms. 



Their production coincides with the appearance of a large amount of young Calanus (of the 

 red Calanus ) . At this time, the spots of "diatom blooming" occur over the entire area of the Nor- 

 wegian Sea. The production of diatoms is of especially long duration on the shoals, in shallows, 

 and in the current eddies . Diatoms usually develop or grow in the thin (3-5 m .) surface layer. 

 When they die they lose their buoyancy and, sinking, concentrate near the thermocline . 



In all regions, the "diatom blooming" usually contains. many young of Calanus finmarchicus , 

 Calanus hyperboreus , Pseudocalanus elongatus , Oithona similis, etc. This enables the herring even 

 during "blooming" to continue their feeding successfully. The feeding herring break up into small 

 schools and keep mostly to depths of 10-15 m. During the summer months, at the borders of the 

 East Icelandic and the East Greenland currents (region of the polar front), one can quite often en- 



132 



