LIFE HISTORY OF LAKE HERRING OF LAKE HURON 



367 



increase in each successive year, except in tlie last one of each series, in all age groups 

 considered. In this year, however, the increase in length begins in 1920 instead of 

 in 1919, as was the case with the preceding years of life. Most of the lengths of the 

 fifth year are the same. An increase is shown for this year in the sLxth age group in 

 1922 and 1923 and in the fifth age group in 1923 and 1924, fish that hatched in 1918 and 

 1919 and m 1919 and 1920, respectively. In the sixth year of life the lengths fluc- 

 tuate more or less with the year classes, although the 6-year fish hatched in 1918 and 

 1919, especially the latter, average larger in 1923 and 1924, respectively, than those 

 hatched before 1918. 



A study of total calculated and actual lengths, then, shows (1) that the herring 

 of Saginaw Bay attained approximately the same length in corresponding years of 

 life durmg the period 1915 to 1918, inclusive; (2) that all fish, with two exceptions 

 (see age groups VI and V, year of life I, of year classes 1919 and 1920, Table 37), 

 three years of age and younger were larger in 1919 and thereafter than were fish of 

 equal age before 1919; (3) that all fish, with exception noted in (2) above, 3 years 

 of age and younger, showed acceleration in growth in 1919 while older fish apparently 

 did not show acceleration in this year; (4) that all fish 3 years of age and younger 

 reached progressively greater lengths each successive year after 1918 (except in the 

 last one of each series, when the average length remained constant, decreased, or 

 increased slightly), while the 4-year fish did likewise after 1919; and (5) that fish 

 older than 4 years hatched after 1917 attained greater average lengths at the same age 

 tJian those hatched before or in 1917, the fifth age group of year class 1918 excepted. 



From a study of both measured and calculated lengths it is concluded that the 

 year 1919 initiated a period of increased growth rate in all Saginaw Bay herring 

 3 years of age or younger. 



Table 38. — Uncorrected calculated length increment attained by various year classes of Saginaw Bay 

 herring during the calendar growth years 1914 to 1924, inclusive. The increments are derived from 

 Table 35  



I The last value of each horizontal row shows the increment reached by November, when fish were captured. 



