366 BULLETIN OF THE BUREAU OF FISHERIES 



length in the first year of life as the three preceding year classes but exceeded them 

 in length in corresponding later years. The 1919 year class (age groups IV,V, VI), 

 however, in general reached greater average lengths at corresponding ages than its 

 predecessors in all years of life. The same tendency to attain greater lengths than 

 its predecessor at corresponding ages is found among the remaining year classes 

 considered. Two exceptions are noted — the rates of growth are approximately the 

 same in the 5-year fish of the 1919 and 1920 year classes and in the 4-year herring 

 of the 1920 and 1921 year classes. It is to be noted, then, that an acceleration in 

 growth occurred in 1919 in the third year of life in the fish of the 1917 year class, in 

 the second year in the fish of the 1918 year class, and in the first year in the fish of 

 the 1919 year class, but apparently not in the fourth year in the 6-year individuals 

 of the 1916 year class; and that the herring of all age groups attained greater lengths 

 in the early years of life after 1919 than before this year. As comparisons are made 

 between fish of the same age groups, the increases in length are believed to be actual 

 and not Lee's "apparent change in growth rate." It appears, then, that the year 

 1919 introduced a period favorable for the growth of herring. 



These facts probably are brought out more clearly in Table 37, in which the 

 data of Table 36 are rearranged so as to group together the lengths of each year 

 of life. Age groups VIII and VII of the year classes 1914 and 1917, respectively, 

 are not considered in the following discussion, as they contain too few individuals to 

 give dependable averages. Table 37 shows that the computed total lengths of the 

 first year of life (115, 117, 113, 116 millimeters) fluctuate with the year classes in 

 the sixth age group. In the fifth age group they remain constant in 1917 and 1918 

 (115 and 114 millimeters), but increase to 119 and 117 millim.eters in 1919 and 1920, 

 respectively. In the fourth age group the length attained in 1918 is about the same 

 as in the older age groups but is greater in 1919 and again in 1920 and 1921. In the 

 second and third age groups there is a progressive increase in length attained at the 

 same age with the successive calendar years. In general, the average lengths of the 

 first year are relatively small and are very nearly the same for all age groups and year 

 classes in the calendar years 1915 to 1918, inclusive, but with one exception' are 

 relatively large in 1919 and increase in each successive year thereafter. 



The total length of the second year of life remains constant in 1917 and 1918 

 but increases in 1919 and 1920 in the sixth age group. It increases progressively 

 for two successive years in the fifth, fourth, and second age groups and then remains 

 the same. In the third age group the total length of the second year increases in 

 1921, then remains virtually constant for two successive years. The average lengths 

 of the second year are appro.ximately the same for all age groups and year classes 

 in the years 1916 to 1918, inclusive, and are smaller than those of the years following 

 1918. 



The total lengths of the third year of life show a progressive increase in each 

 successive year, e.xceptin tJie last one of each series, when they either remain constant 

 or decrease shghtly, in all age groups considered. As was the case in the lengths 

 of the first and second years of life, those of the third year are about the same for the 

 age groups in the years preceding 1919 and are smaller than those of the years follow- 

 ing 1918. The average lengths of the fourth year of fife also show a progressive 



' See footnote 4, p. 363, 



