372 



BULLETIN OF THE BUREAU OF FISHERIES 



fifth years of life (28 and 21 millimeters) than did those of the same age hatched in 

 1917 and 1918 in the corresponding years (26 and 18 milUmeters and 25 and 19 

 millimeters) and at the same rate in the third, fourth, and fifth years as the 6-year 

 herring hatched in 1919. It shows, also, that the slow-growing fish of the fifth age 

 group grew no faster in the third, fourth, and fifth years than the fast-growing fish of 

 that age group. The fourth and third age groups, however, seem to show a decided 

 compensating growth. In the former age group the order of the succession of the 

 amount of growth of the first year for the four year classes is exactly reversed in the 

 second and third years, while that of the latter age group is reversed in the second 

 year. A further indication of compensation is seen in Table 36, which shows that the 

 difference between the final total lengths of the adults of an age group was, in general, 

 less than that between the computed lengths of the earlier years of these fish. This 

 appears by comparing the 4-year fish of 1918, 1919, 1920, and 1921; but the differ- 

 ences between earlier years seldom were compensated entirely at death. The big 

 juveniles were, on the average, also the big adults, and the slow-growing young fish 

 seldom reached the length of the fast-growing ones in corresponding adult years. 

 Thus, at firet sight it seems that the evidence for the law of growth compensation 

 is conflicting for the lake herring. 



Table 41. — Computed average total length and average increment of length for each year of life for 

 each of three size groups of the 4-ye.ar herring taken at Bay City, Mich., in 19SS. The size 

 grojtps are based on lengths at the end of the first year of life 



Note. — The last total length value of each horizontal row is derived from direct measurements of fish. 



In spite of the apparently conflicting evidence of the last paragraph, that com- 

 pensation in growth occurs in the herring seems clear from Table 41. The computed 

 lengths of the first year of the 4-year herring taken in 1923 were divided into three 

 size groups, each group including appro.ximately the same number of fish. The 

 average length of the fish of each size group was then determined for each year of 

 life. From these total lengths the average annual increments were derived. It 

 may be seen from this table that the big yearlings were, on the average, the big fish 

 in all succeeding years, but that the differences between the lengths of the three 

 size groups diminished each year, so that the fish became more uniform in size each 

 successive year of age. Or, as seen from the increments, the smallest yearlings were 

 the fastest growing fish and the largest yearhngs the slowest. 



We may reverse the procedure employed in Table 41 and divide the actual 

 lengths at death (instead of the computed lengths of the first year) into size groups. 

 We may then average the computed length and increment values of each size group 

 for each year of life, as shown in Table 42. We find on examining these computed 

 values (1) that the large fish of an age group were the large fish in each preceding 



