354 



BULLETIN OF THE BUREAU OF FISHERIES 



Gravelly Point fish, and 92.4 per cent of the Au Gres sample, or, in general, 84.7 per 

 cent of all the fish taken by me in this year. In each year the fourth age group was 

 the largest, its individuals comprising 42.8 to 58.3 per cent of the total catch. It is 

 to be noted that the percentage of 3-year fish increased each year during the period 

 1921 to 1923 (14.3 to 29.5 to 32.8 per cent); then, in general, remained stationary 

 (32.7 per cent, 1924 combined) in 1924, though it dropped to 26.5 per cent in the 

 Tobico and Nayanquing material. This general increase in the number of 3-year 

 herring occurred at the expense of the 5-year fish mainly, which each year became 

 progressively less abundant (30.1 to 19.0 to 17.3 to 11.8 per cent (1924 combined); 

 Tobico and Nayanquing, 12.1 per cent). The percentage of 4-year herring remained 

 virtually the same in all samples, except those of Tobico and Nayanquing, in which 

 it is comparatively high (58.3 per cent), which fact, no doubt, accounts for the drop 

 in the percentage of the 3-year fish of this sample. The probabje significance of 

 the gradual shifting in the age composition of the commercial catches is discussed 

 on page 355. The frequency distribution according to age groups and the shifting 

 in the age component are graphically shown in Figure 16. The 1922 and 1923 curves 

 are nearly the same. (For illustrations of typical scales of herring of the various 

 age groups see figs. 17-36.) 



Table 30. — Summary of the frequency dislribulion of Saginaw Bay herring according to year class and 



age group 



' Tobico and Nayanquing samples combined. 

 ' Gravelly Point herring. 



' Au Ores herring. 

 ' 1, 2, and 3 combined. 



YEAR CLASSES 



The upper part of Table 30 shows the total number of individuals in each year 

 class of each sample taken in 1921, 1922, 1923, and 1924; the percentage of this total in 

 the whole number is shown for each sample. The year classes are shown in chrono- 

 logical order, beginning with the oldest fish (8-year fish) hatched from eggs laid in 



