LIFE HISTORY OF LAKE HERHING OF LAKE HURON 415 



females than of the males of a year class reach sexual maturation for the first time 

 in the third year — that is, the females mature earlier in life than the males. 



42. About 3 per cent of all the herring taken in the samples from Saginaw Bay 

 were sexually immature or nonspawning fish. 



43. The majority of the lake herring attain sexual maturity in the third and 

 fourth years of life. Fewer reach it in the fifth year. Very few individuals reach 

 sexual maturity in their second j'ear. All herring of the sixth and older age groups 

 are sexually mature. 



44. The lake herring taken in 1924 at the same locality in Saginaw Bay but on 

 different dates show no consistent differences in size, rate of growth, and age com- 

 position. These facts indicate that the character of the herring stock of one locality 

 in the bay does not change during the spawning run. 



45. The herring population of Saginaw Bay can not, on the basis of growth rate, 

 be separated into distinct races. 



4G. Distinct differences exist between the growth rates of the herring of some 

 localities in Lake Huron. This suggests that there may be distinct races of herring 

 in Lake Huron and that the migrations of the herring are more or less local. 



47. Saginaw Bay produces, so far as known, the most rapidly growing herring in 

 Lake Huron. Of the various localities in Lake Huron considei'ed, the herring of 

 Oscoda rank second in rate of growth, t.hose of Alpena, St. Ignace, and Killarney 

 third, and tliose of Wiarton fourth. Tlie different growth rates of t.he herring of 

 tJicse localities possibly may be correlated with the different conditions of life. 



48. The average measured length of the herring schools of Saginaw Bay tended 

 to increase each year during the period 1921 to 1924. 



49. The average measured length and weight of herring of corresponding age 

 groups increased progressively each year during the period 1921 to 1924. 



50. A study of the computed lengths and increments of the Saginaw Bay herring 

 shows: (a) that in each of the years 1915 to 1918, inclusive, the rate of growth of 

 herring in the first year of life was the same; (b) that in the year 1919 the growth 

 rate was increased in herring 1, 2, and 3 years of age; (c) that neither in 1919 nor 

 subsequently did the growth rate of fisli older than 3 years increase; (d) that the 

 acceleration of growth rate initiated in 1919 in fish 3 years of age and younger con- 

 tinued in the years 1920, 1921, and 1922; (e) that in the period 1919 to 1922, inclu- 

 sive, fish in their first year of life, in general, grew more rapidly each successive year 

 (during this period tJiere was progressive increase of growth rate in 1-year fish, 

 although in 1922 the increase was very slight — 1 millimeter); (J) that during the 

 period 1919 to 1923, inclusive, the growth rate of the second and third year fish did 

 not increase in successive years but remained virtually constant at the increased rate 

 attained in 1919; (g) that the growth rate for the fourth and later years likewise 

 tended to remain constant in the years 1919 to 1924, inclusive; (h) that all fish 3 years 

 of age and younger in general reached progressively greater lengths each successive 

 year after 1918, while the 4-year fish did lilcewise after 1919; and (i) that fish older 

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

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



