In April, the temperamre reaches a minimum. At this time, only immature herring occur 

 in the Barents Sea; in the western part there are also some spent herring. 



EXiring this period, herring with the sexual products well developed and spawning herring 

 are distributed along the northwestern coast of Norway (according to the observations in 1939 from 

 the trawler "Beluga" from North Cape to Ringvass^; in this period the temperature was above 5°C. 

 Near the bottom the herring spawned at the same temperature) . 



After the spawning, the herring in large schools migrate to the feeding areas, following the 

 North Cape current to the northwestern parts of the Barents Sea, and the Spitsbergen current to the 

 area near western Spitsbergen, to 78 degrees N., possibly still farther. 



Near the surface, the temperature Is now rapidly increasing, and a great quantity of zoo- 

 plankton, the main food of the herring, appears . We shall once more recall that the movement of 

 the herring is induced, not so much by the warming of the water, which took place in the north- 

 western area, but mainly by the physiological stage of the herring, i.e., the demand for more 

 energy because of the hig^ catabollsm during the maturing and spawning. 



"ITiis demand for increased feeding following spawning Is connected with certain temperature 

 conditions. This correlation cannot be measured quantitatively, as we still do not know the opti- 

 mum feeding temperature for the herring. 



In summer, the herring are dispersed over a wide area of the southern Barents Sea. The 

 temperature of the surface layers reaches a maximum in July- August, that of the deeper layers in 

 September -October. During all this time, there is an intensive development of the gonads. 



In young herring which have not yet spawned, the ovaries pass from stage I to 11; in imma- 

 ture herring, 4-5 years of age, from II to III. In herring which spawned during the spring, empty 

 follicles and eggs which were not spawned, are now resorbed, and simultaneously the ovocytes are 

 ripening, i.e., there is a transition from stage n to m. 



At the beginning of the winter, herring with developing gonads (stages HI and IV) as already 

 mentioned, migrate westwards, as the water starts cooling. Along the border-line of the Nor- 

 wegian Sea and near the spawning places, pre-spawnlng concentrations are formed at a higjier 

 temperature. Only immature herring, which will not spawn In spring, are found in the east. 



The Influence of Salinity 



Investigations on salmon, eel, sterlet, and other fishes have shown that the osmotic pres- 

 sure of the blood is dependent on the salinity. During the course of the year, the salinity of the 

 Barents Sea varies, and this variation is influencing the herring. In May -July, when the sea re- 

 ceives most admixture of fresh water, the mature herring migrate to the western areas (Flnmark 

 Bank, the Demidov and Nordkyn Banks). Farther to the east, no concentrations of adult herring 

 have been observed, nor have any spent herring been found near the coast, where the water is less 

 saline. 



In summer, the salinity Is comparatively low in the eastern areas, in the Kanin-Kolgujev 

 area, below 34° /oo in July 1938. At the same time, the salinity near the Murmansk coast was be- 

 low 32°/oo. The gradual increase in salinity, beginning in August, coincides with an intensive de- 

 velopment of the gonads in the maturing herring. In analogy with what has been observed in other 

 fishes (salmon, eel, sturgeons and others (Betesheva 5)), we may assume that the osmotic press- 

 ure in the blood of the Murmansk herring is directly correlated with the salinity of the water. The 



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