LIFE HISTORY OF LAKE HERRING OF LAKE HURON 



369 



Table 39. — Computed average length increments reached in different yearn of life hy various age groups 

 of Saginaw Bay herring. The data are those of Table 38 rearranged so as to group the increments 

 of the same year of life together — Continued 



*> Increment up to November when captured. 



The increasingly greater mean lengths of the 2, 3, and 4 year fish after the year 

 1918, noted above and shown in Table 37, are thus due largely, if not entirely, to the 

 accelerated growth of the first year of life. To illustrate this, we may compare, for 

 example, the growth rates of the 3-year herring of the year classes 1919 to 1922, 

 inclusive. At death the fish of each year class averaged 224, 229, 233, and 236 milli- 

 meters, respective^, in length (Table 34). From Table 39 it may be seen that they 

 grew 127, 139, 142, and 143 millimeters, respectively, in their first year of life; 65, 

 61, 59, and 59 milhmeters, respectively, in their second year; and 32, 29, 32, 

 and 34 millimeters, respectively, in their third year. It is evident that the large 

 size of the 3-year fish of the 1921 or 1922 year class was not due to an increase in the 

 growth rates of the second and tliird years of life but wholly to the increase in the 

 growth rate of the first year. Similarly, the greater average length of the 3-year fish 

 of the 1920 year class was due entirely to the acceleration in growth of the first year 

 of life. Similar results may be obtained from a study of the increments of the second 

 and fourth age groups. In the age groups considered, the relative size of the mature 

 fish was correlated with the size reached by them at the end of the first year of life. 

 The growth history of the 1-year fish was then of great significance to the herring 

 fisheries of 1921 to 1924, inclusive. The growth rate of the first year determined 

 largely the size, and indirectly the weight, of most of the individuals of the commercial 

 catches of these years, for, as has been shown (Table 30), the bulk of these catches 

 consisted of fish of years III and IV. If the growth rate of the first year general^ 

 controls the size and weight of the 3 and 4 year herring, then, from the point of view 

 of the fisheries, the growth history of the herring of year I is especially significant; 

 for, not only do the herring complete nearly 50 per cent of their growth in length 

 in the first year of life, as I shall show later, but the rate of growth of tliis year 

 would determine the size and weiglit of most of the individuals taken in the 

 commercial nets. 



