the North Sea, to the west from the Shetland Islands, In the area of offshore shelf of the Faeroes 

 and along the southern coast of Iceland. Spawning is observed at the end of the winter - in early 

 spring at the depths ranging from several tens of meters to 200-225 m., at a temperature of 6-7.5 

 and salinity of 33-35 per cent. The most intensive spawning occurs at the depth where waters of 

 Atlantic origin meet the littoral waters . The main spawning grounds are now located along the 

 south-western coast of Norway. 



4. The passive drift of larvae and fry resulting in their dissemination over vast territories 

 during the first year of their existence plays an important role in the life of Atlantic -Scandinavian 

 herring. The drift of fry has been most thorougjily studied in the Barents Sea to which fry from 

 Lofoten region are carried in the course of 150-200 days . The fry from southern Norwegian spawn- 

 ing grounds drift to the northern shores of the Scandinavian peninsula . 



5. Having grown and matured, the young herring proceed to the places of their origin. The 

 date on which return migration begins depends to a great extent on the growth rate and the size of 

 the fish. In the Barents Sea, 5-year-old herring reach 22.5-23.0 cm. in length, in the Norwegian 

 Sea the herring of identical age are 27.5-28.0 cm. in length. In view of the aforesaid, the herring 

 from the Norwegian Sea become sexually mature at the age of 4-5 years, whereas herring in the 

 Barents Sea attain sexual maturity at the age of 5-6 years. Individual specimens that were delayed 

 in their development mature at the age of 7-8, even 9 years. 



6. Sexually immature herring migrate to the open sections of the sea 1-2 years prior to the 

 occurrence of sexual maturity . In the Barents basin they are found in greatest numbers in the 

 western zone of the sea. A great number of young maturing herring populate the north-eastern arm 

 of the Norwegian Sea, south from Mohn's Threshold. Spawning grounds of first-time spawners are 

 located in the proximity of their feeding grounds . 



7. Migrations of adult Atlantic -Scandinavian herring into the north latitudes are associated 

 with feeding. The feeding takes place in the most productive zone of the North- European basin, in 

 the region of the polar front and adjacent areas, where, as a result of the intensive vertical cir- 

 culation of water volumes, there are formed outstandingly favorable conditions for plankton develop- 

 ment. 



8 . The rhythm of feeding migrations of the older age groups of Atlantic -Scandinavian her- 

 ring is coordinated with the vernal processes of the plankton development when the warm- and cold 

 water Calanus reproduce in the surface layer. Migration periods of young first-time spawners 

 coincide with the development of red Calanus . Older age groups feed also in polar waters beyond 

 the borderline of the polar front. The frontiers of their area of dissemination extend as far as the 

 edge of the floating ice. E)uring the feeding season, young herring 6-7 years of age travel as far as 

 the edge of the polar ice, but rarely beyond. 



9. During a migration in search of food, the physiological state of herring drastically 

 changes. The herring, exhausted by spawning, lose almost all their fat reserves . During that 

 period, their fattiness ratio drops to 0.9-0.8. Over the course of 3.-3.5 months during the feeding 

 season the weight of herring rises 25-30 per cent. Their fattiness ratio increases to 1,2-1.3. 

 Herring reach their maximum fattiness indices in late July-early August, when the proportion of 

 fat to the overall body weight amounts to 18-20 per cent. From that moment on, the gonads begin 

 developing intensively. By September, the maturity factor reaches, in males 11-12 per cent, in 

 females - 6.8 per cent of the body wei^t. The southward migration of the herring schools to the 

 spawning grounds coincides with the latter period. 



10. Migration paths of maturing herring pass across the western zone of the Norwegian Sea, 



61 



