After the restoration of the gonads at the beginning of the new sexual cycle Ouly, stage 

 11-111), there is a corresponding decrease of the phagocyte cells of the leucocytes. 



The Ecological Conditions and the Speed of Maturing 

 of the Sexual Products 



As long as the sexual products have not developed beyond stage IV, the immature Murmansk 

 herring do not migrate outside the Barents Sea. On the other side, the adult herring form pre- 

 spawning concentrations in the Norwegian Sea, spawn along the coast of northern Norway, and then 

 migrate to westel'n Spitsbergen, where they feed some 4 months. The living conditions for the 

 mature herring near Spitsbergen and in the Barents Sea are not uniform, the distance between these 

 two areas being nearly a thousand kilometres. 



The habitat of the adult Murmansk herring reaches the 78 degrees N., and westwards from 

 the coast of Spitsbergen to the zero meridian . 



In the absence of direct observations, the living conditions of the herring before or during 

 the spawning cannot be discussed. 



The immature Murmansk herring live in an area in main limited by the 75 degrees N. lat., 

 25 degrees E. long., and 50 degrees E. long. The Spitsbergen branch of the Atlantic current is 

 of great importance for the hydrographic conditions in the Bear Island-Spitsbergen area, while the 

 North Cape current influences the southern part of the Barents Sea. 



The sea water in the Spitsbergen area is very similar to that of the North Atlantic (trans- 

 parency, color, salinity, and temperature). The coast water near the Murmansk coast is colder 

 and less saline, being near to the continental shelf. This explains the well-known earlier develop- 

 ment of plankton along the Norwegian coast and the coast of western Spitsbergen. TTie farther into 

 the Barents Sea, the later the mass development of the zooplankton. From this it follows that the 

 food uptake of the herring is different in the two areas. Finally, the great difference in the magni- 

 tude of the solar radiation emphasizes the dissimilarity between the two areas. 



It is concluded that the feeding period of the herring is shorter near western Spitsbergen 

 than along the Murmansk coast. If the summer is shorter, but the hydrographic conditions more 

 favorable, the development of the plankton takes place more rapidly, the herring are feeding more 

 intensively, fattening in shorter time. 



Accordingly, all the physiological processes will proceed more rapidly in the mature her- 

 ring than in the immature individuals . Our observations indicate that the mature herring pass into 

 stage III at the beginning of July. In the immature herring, the ovaries do not begin to ripen until 

 the end of July /beginning of August. The final ripening of the ovaries will accordingly take place 

 one month earlier in the mature herring than in the small, immature individuals. This is the ex- 

 planation why large adult herring arrive in the spawning area earlier than the younger first-time 

 spawners . 



The separation of the two groups creates favorable conditions for a better utilization of the 

 spawning area, and is evidently also of impwrtance in securing the food conditions for the numer- 

 ous offspring, especially before they leave the spawning area . 



The herring begin to feed intensively in April, the maximum in the amount of food in the 

 stomachs is observed in May, and the decrease in July. During the feeding period, fat is accumu- 

 lated on the intestines, with a maximum accumulation in the autumn. At the end of July, great 



245 



