In the eastern and northern regions of the sea the phenomenon of homotherm occurs earlier, 

 as a result of which the fry descend to the benthipelagic levels at an earlier date. As a rule, by 

 the end of January the herring fry hatched during the current year remain in benthic levels in all 

 the zones of the Barents Sea. This period of life of young herring has been studied in detail by 

 Prof. V. R. Aleev (3) and V. N. Tikhonov (27, 28, 29). 



The exceptionally great eurythermal ability of herring fry should be regarded as adapta- 

 bility that has been developed as a result of natural selection. Without this adaptation, the drift of 

 herring larvae into the northern peripheries of the Atlantic Ocean could not have been accomplish- 

 ed as it would inevitably result in the death of the majority of young hatched that year, which prob- 

 ably did occur in the past, while the migration was in process of formation. 



The great eurythermal ability of young herring determines first of all the duration of the 

 growing period, which has been described by G . V. Boldovskiy (8) and confirmed by the data obtain- 

 ed through the study of scale growth carried out by N. Solovyeva (25) and Murashkintseva (18). In 

 connection with the lengthy feeding period of young herring the need to accumulate fat reserves is 

 excluded (34). The organism utilized all resources for growth purposes. 



The living conditions for young herring in the Norwegian coastal zone are more uniform, 

 althou^ temperature conditions in fjords of the northern provinces are, of course, more severe. 



When studying factors responsible for fluctuations in number of different generations of 

 Norwegian herring, Hjort (50) voiced the supposition that too extensive migrations of fry are un- 

 favorable and may result in young fish eventually finding themselves under conditions unsuitable 

 for their existence. Hjort wrote that it would be desirable to find out over what distance the fry 

 migrate and the possibility of reaching areas where the living conditions are favorable. 



The exceptional adaptibility of fry to life under diverse conditions of external environment, 

 first of all low temperature, led us to believe that even in Barents Sea, which is the most severe 

 region of the northern Atlantic, there are no zones where living conditions are lethal for young 

 herring. Whatever the distance which the fry migrate, the ultimate point of passive drift is always 

 close to Atlantic waters. A year earlier or a year later, depending upon the feeding conditions and 

 the growth rate, the herring fry return to the places where they were hatched. 



Of course, the survival rate of fry in different sections of their area of dissemination is un- 

 equal, however, the main reason for the death of fry is not in abiotic factors, but in the activity of 

 numerous and diverse predators, first of all the cod. 



GROWTH OF YOUNG HERRING AND BEGINNING OF RETURN MIGRATION. 



The second year of existence is characterized by active settlement of young herring. In the 

 Barents Sea, two-year-old herring penetrate particularly far to the south-east, into Chesha Bay, 

 shallow Pechora regions, including the Pechora River estuary, and drift into the Kara Sea via Kara 

 Strait and Yugorski Shar . 



Occasionally they enter the bays ^nd gulfs of the Murman coast in great numbers. 



In the White Sea, two-year-old specimens of Murman herring are found with the White Sea 

 herring fry. Young herring enter particularly willingly the relatively warm zones, where the 

 waters have a low salinity. The winter dissemination of the two-year-old fish is as extensive as 

 summer dissemination. We also encounter the herring of that age at Persey Bank, beyond 77 of 

 northern latitude, along the shores of Novaya Zemlya and in the White Sea. 



19 



