364 



BULLETIN OF THE BUREAU OF FISHERIES 



Table 37. — Computed lengths reached at end of different years of life by various age groups of Saginaw 

 Bay herring. The data are those of Table 36 rearranged so as to group the lengths of each year of 

 life together ' 



' The number of specimens employed is shown in parentheses. 



' Actual length when captured in November. 



Tables 35 to 37 have been compiled to find whether the more extensive data 

 derived from calculated lengths afford evidence of a change in growth rate. In 

 Table 35 the year classes are arranged chronologically, so that the various age groups 

 of each year class are brought together. The fish of the various age groups of the 1918 

 year class are seen to have been 113, 114, and 116 millimeters long at the end of their 

 first year (1918), while those of the 1919 year class were 116, 119, 122, and 127 milli- 

 meters long at the same age; that is, in 1919. This apparent increase in length in 

 1919 continues for the first-year fish of 1920, 1921, and 1922, the figures being 117, 

 133, 139, and 121 for 1920, 136, 142, and 141 for 1921, and 143 and 137 for 1922. Simi- 

 lar increases in length in fish of the same age in successive years appear in fish in their 

 second, third, fourth, and fifth years. Mere inspection of the figures as they stand in 

 Table 35 seems, then, to strengthen, from calculated lengths, the view suggested by the 

 measured lengths of Table 34 that the growth rate of the herring increased after 1918; 

 but Table 35 seems also to show evidence of Lee's phenomenon — that lengths calculated 

 for a given year from scales of young fish are always greater than lengths calculated 

 for the same year from older fish. Thus, the 1919 year class of Table 35 shows age 



