TABLE 2 . THE MEAN AGE COMPOSITION OF THE SPAWNING POPULATION 

 OF SMALL WHITE SEA HERRING (IN PERCENTAGES). 



In the first period of fishery from 1923 to 1934, the great mass of the spring population of 

 small Kandalaksha herring consisted of 3 age groups: 4-year-old fish in first place; 3-year-oId 

 fish; and 5-year-old fish. In the second period from 1935 to 1950, the great mass of herring was 

 composed of 2-year-old, 3-year-old and 4-year-old fish. The number of 5-year-old and 6-ye£ir- 

 old fish had fallen sharply . 



If, in 1923-1924, herring over 4 years old constituted 35.9%, in 1935-1950 they only con- 

 stituted 4.7%; on the other hand, the number of younger herring, 2-year-old. and 3-year-old, 

 rose in the second period to 72% as against 26% in the first period. The number of 2-year-old fish 

 rose especially sharply. In the sjiawning- population of small Kandalaksha herring in 1923-1934, 

 2-year-old fish were hardly found at all, but in 1935-1950 they constituted a fifth of the spawning 

 population. 



Thus observations over many ye^rs have shown that in the last period the age composition 

 of the small Kandalaksha herring has greatly changed (see Figure). 



If before 1934 the predominance of one and the same year class over a series of years was 

 strongly marked, since 1935, on the other hand, the fishery has been based every year on the 

 catch of two-year-old and three -year old fish. 



The 1919, 1924, 1927, and 1930 year classes were all extremely numerous, and each one 

 of them predominated in the composition of the spawning population for several years . Thus the 

 1919 year class constituted the main part of the spawning population from 1923 to 1926; the 1924 

 year class, from 1927 to 1930; and the 1927 year class, from 1930 to 1932. 



In the years 1934-1950, the age composition of the spawning population became more iml- 

 form. The influence of individual numerically strong year classes was no longer to be seen, and 

 the spawning population began to consist each year of three -year -old fish, i.e., each time of a new 

 year class . 



The simplification of the composition of the spawning population caused a sharp lowering of 

 the number of small Kandalaksha herring and resulted in a dec;rease in the reproductive capacity 

 of the species and a drop in catches. 



TTie structure of the spawning population of the smaU herring of Dvina Gulf has also changed 



277 



