South of 74° north latitude, in the vicinity of Mohn's Threshold, we encountered in the course 

 of the entire period of observations, i.e . from 1950 to 1954, younger herring at the age of 6 to 10 

 years. 



Farther to the west, beyond the zero meridian, in the region adjacent to Jan Mayen, the age 

 cp^mposition of catches is characterized by a great admixture of fishes of the older age groups . 



Thus, the theory maintaining that young sexually mature herring accomplish but limited feed- 

 ing migrations may be now considered as an established fact. The Bear-Spitsbergen region and 

 polar waters beyond Mohn's Threshold are not visited by the first-time spawners. They feed south 

 of 73-72 , north latitude within the limits of the Norwegian Sea. 



Our theories concerning the possibilities of fishing on such herring may be reduced to the 

 following: when the middle-aged fish are represented by few year classes, the older fish groups 

 determine the maximum success of fishing. When, however, 6-7-year-old herring are represent- 

 ed by abundant year classes, they may be of a greater impor nee than the herring of older age 

 groups. In each individual case, this problem must be solved with the help of corresponding in- 

 vestigations, during which the magnitudes of remainder and recruitment are taken into account^ 



FEEDING OF HERRING AND CHANGES OCCURRING 



IN THEIR PHYSIOLOGICAL CONDITION 



Our investigations enabled us to clarify certain details of feeding migrations, first of all, to 

 show the drastic changes occurring in the physiological condition of adult herring, which determine 

 the character of such migrations . 



The main spawning taking place off the south-western coast of Norway and in the vicinity of 

 islands is completed in late March. At the beginning of April we found on the spawning grounds 

 only a small number of first-time spawners that spawn at a later date. 



Feeding migrations proceed down the current, which facilitates the movement of herring. 

 The speed of their swimming exceeds the current's mean velocity, and the schools pass every day 

 from the warmer to the cooler waters . All the populations of ocean herrine reproduce at a temper- 

 ature of 5-7°. Searching for food, the herring that have spawned during the first half of the sum- 

 mer may enter the waters having a temperature of 3°. In mid-June, 1941, Captain V. A. Egorov 

 discovered herring concentrations south-west of Spitsbergen, where the temperature was 2.8° ^^ 

 early June 1954, herring concentrations were observed in the zone of Bank "774" at the temperature 

 of 2'^. 



According to E. A. Pavshtiks, the feeding migrations of herring are closely related to the 

 pattern of plankton production in the Norwegian and Greenland seas . 



As is well known, the annual cycle of the plankton production may be divided into four periods 

 corresponding to different hydrological seasons: i.e. winter, spring, summer, and autumn. 



During the biological winter, which corresponds to the hydrological winter, the main biilk of 



J/ In 1955, these assumptions have been confirmed. The intensive replenishment of an adult 

 school by representatives of the abundant 1950 year class ensured hig^ herring catches at the 

 end of the feeding season, southerly from Mohn's Threshold. The 1950 year class formed on 

 an average 45 per cent of the 1955 catches . 



34 



