With the changes in physiological condition, there arise in herring new reactions to the 

 external environment -- temperature and currents in particular. As we have mentioned above, at 

 the end of spawning the herring move along with the current and spread in relatively cold waters. 

 From mid-July, the well fed herring with gonads in the process of restoration discontinue moving 

 northwards (down the current) and concentrate near warm Atlantic waters . 



The change in the direction of migration in the northern half of the Spitsbergen current 

 occurs between July 10 and 20. During the early half of July, over the entire area of the Spitsbergen 

 current, the herring begin migrating in the northern direction; however, they discontinue the 

 movement north of 74° north latitude. South of 74° north latitude, the herring continue moving to 

 the north until the end of July. August is marked in all the regions by the beginning of mass migra- 

 tion of herring in the southern direction. 



The date on which the return movement of herring schools to the spawning grounds begins 

 is determined to a considerable extent by the feeding conditions . 



MIGRATION PATHS AND MAIN FEEDING GROUNDS 



OF ADULT HERRING 



The study of migratory habits of herrinjj required extensive oceanographic investigations 

 directed at defining more precisely the pattern of the constantly active currents. Such investi- 

 gations were conducted during the last few years simultaneously with oceanographic observations . 



A map of the currents of the Norwegian and Greenland seas was drawn at the beginning of 

 our century by Norwegian scientists Helland-Hansen and Nansen (49). Following the said scheme, 

 the warm waters of the Atlantic current, having passed the Faeroe-Shetland channel, proceed to 

 the north-east, along the continental slope of the Scandinavian peninsula. Approximately at the 

 latitude of the Lofoten Islands, a branch of that current deviates towards the west forming a large 

 eddy in the central zone of the Norwegian Sea. The remaining waters continue flowing to the 

 western shores of Spitsbergen and form a second eddy near Nansen Threshold, this time within the 

 borders of the Greenland Sea. Near Andj^y Island, a branch deflects from the Norwegian current 

 and proceeds into the Barents Sea. This is the North Cape current. A part of the waters of the 

 Spitsbergen current flow into the Arctic ocean. In the western half of the basin, there passes the 

 cold Greenland current descending to the south along the shores of Greenland, north of Iceland a 

 portion of these waters turns to the south-east and proceeds to the Faeroes in the form of the east- 

 Icelandic current. 



It is important to note that according to the scheme of Helland-Hansen and Nansen in the 

 western half of the Norwegian Sea, beyond the fifth meridian of east longitude, there exists a system 

 of vigorous vortices and no streams flowing in the northern direction. That scheme has been some- 

 what improved by Soviet researchers V. A. Perezkin (7) and V. T. Timofeev (26). 



Investigations of the Polar Institute have shown that the scheme of Helland-Hansen and 

 Nansen requires additional corrections . Having developed the vast oceanographic information 

 available, B. V, Istoshin and A. P. Alekseev suggested the following pattern of currents in the 

 studied region.—' 



The Norwegian current divides in the southern half of the Norwegian Sea into two large 

 branches - western and eastern. The former branch proceeds to the north approximately along the 

 zero meridian and, near Mohn's Threshold, forms several branches flowing in western direction. 

 _1/ The article appears in the present symposium. 



38 



