The 1904 year class was exceptionally strong for both the Norwegian school, which spawned 

 off the south-western shore of Norway, as well as for the herring that spawned in the region of 

 Iceland (42, 70) and the gulf of St. Laurence, on the western shores of the Atlantic (55). 



The next strong year class, hatched in 1918, was abundant along the Norwegian shore, 

 Murman coast, and Icelandic region. During the more recent period, strong herring year classes 

 were produced in all the three regions in 1930, 1937, 1938 and 1943. 



We are firmly convinced that different schools of the ocean herring may be identified with 

 precision only through a step-by-step study of the propagation and migration of different year 

 classes. Moreover, that task may be facilitated if we succeed in studying in detail some excep- 

 tionally strong year class . Mass tagging of herring would also be of great assistance in our work. 



The degree of isolation of different schools of Atlantic -Scandinavian herring varies in the 

 course of their existence. We believe it possible to express the following considerations on that 

 subject . There is no doubt that spawning grounds of ocean herring were observed between the 

 Lofoten Islands and the south-western shore of Norway. The spawning grounds situated along 

 Iceland's southern coast, i.e. located in a different system of Atlantic current, are isolated from 

 each other to a still greater extent. The spawning grounds in the vicinity of the Faeroes are sepa- 

 rated from Iceland and Norway by great depths. The spawning grounds along the south-western 

 coast of Norway and on Viking Bank are located considerably closer to each other and characterized 

 by similar conditions . They are situated ou both sides of the Norwegian channel: the former - on 

 the slope of the continental shelf of the Scandinavian peninsula, the latter - on the western slope of 

 the Norwegian channel, within the borders of the continental shelf of the North Sea. 



The direction of the drift of fry from the spawning grounds may be considered relatively 

 constant. The extent of drift, however, may vary considerably, as demonstrated in the example 

 of the Barents Sea. Thus, the isolation of younger age groups is an undoubted fact. We wish to 

 emphasize that the isolated character of the distribution of younger age groups of herring is here 

 understood as the relatively isolated existence of the main bulk of fry of different schools . 



The recently matured herring reproduce, of course, on the spawning grounds most closely 

 situated to their feeding grounds . After sexual maturity has been attained, the migration routes of 

 different populations are separate to a somewhat lesser extent. 



The mass tagging of cod conducted by the Polar Institute and foreign scientists for a number 

 of years, showed that different populations, even the populations located at great distances from 

 each other, may become intermixed. TSning (77, 79) presented data on cod migration from the 

 region of Iceland to Newfoundland, Faeroes, and Lofoten Islands. He also observed the migration 

 of cod from Jan Mayen to Iceland. The migration of cod from the Barents Sea to the south-western 

 coast of Norway was established by Idel'son (11). N. A. Maslov (16) reported that the cod tagged 

 in an arm of Motovka gulf (where it was caught among spawning specimens) migrated to the Lofoten 

 Islands . 



There also exist data on the cod migration from the western shores of Greenland to Kanin 

 Nos. The cod covered the above distance at the end of a migration that lasted for 7 years (47). 



Cod migrations are much more closely connected with the continental shelf than herring 

 migrations. Nevertheless, migrations of cod from one region to another have been observed for 

 the entire North Atlantic territory. Consequently, intermixing of different populations is even more 

 probable in the case of herring, taking into account the extensive feeding grounds and great lon- 

 gevity of these fish . 



48 



