414 BULLETIN OF THE BUREAU OF FISHERIES 



30. A year class predominated for one year only in the commercial catches of 

 the Saginaw Bay lake herring. Each year class dropped off rapidly in the yeai's fol- 

 lowing the year of its dominance — the fourth. 



3 1 . The biological data suggest that commercial fishing for herring is very intense. 

 The symptoms of heavy fishing are: The paucity of old individuals (28), the shifting 

 in the age composition of the samples (29), and the one-year dominance of a year class 

 (30). 



32. In lake herring males and females of an age group grow at the same rate in 

 all years of life. 



33. The sexually mature female herring weigh, on the average, slightly more than 

 the sexually mature male herring of the same age group. 



34. In the Oscoda sample of 1922 the nonspawners of an age group average less 

 in length than the spawners of that age group. 



35. The lake herring grows most rapidly in length during the first two years of 

 life; nearly 50 per cent of the length reached in the sixth year is completed at the end 

 of the first growth year. The data indicate that the growth rate of the first year 

 of life determined largely the size, and indirectly the weight, of most of the individuals 

 of the commercial catches studied (p. 369). From the point of view of the fisheries, the 

 growth history of the 1-year fish is of extreme significance. The first prominent 

 break in the curve of total growth in length occurs in the third year — the year during 

 which sexual maturity is first attained by many individuals. The lake herring reaches 

 at the end of the second year nearly 50 per cent of the weight attained in the sixth. 



36. From the point of view of the commercial fisheries, it is not profitable to 

 allow the herring at their present rate of growth to become much older than 3 or 4 

 years, for the increase in weight in the fourth and fifth years together is less than that 

 of the third year alone. If the nets are so regulated that they take no fish under 4 

 years of age (235 millimeters, or 9.3 inches long, measured snout to base of caudal, 

 and 5.61 ounces in weight), then many herring can spawn twice and a greater number 

 can spawn once, thus insuring the perpetuation of the species, provided the number 

 of spawners is not reduced below the number required for the maintenance of 

 the species. 



37. In lake herring the big yearlings of a year class are, on the average, the big 

 fish in all succeeding years of life, but the differences between the small and large 

 yearlings diminish each year of age — that is, the small yearlings are rapid growers, 

 the large yearlings slow growers. (Gilbert's law of growth compensation.) 



38. The length-weight relationship of lake herring taken just before spawning 

 in the fall can be expressed satisfactorily by the formula 1^=^;. U, in which Ic has a 

 value of 0.01126. 



39. Of the 2,950 lake herring taken in Saginaw Bay 49.5 per cent were males and 

 50.5 per cent females. 



40. The relative abundance of male and female herring varies during the course 

 of the spawning run. Males are more numerous than females early in the season 

 but less numerous late in the season. 



41 . The relative abundance of male and female herring varies with the age groups. 

 In general the males become relatively more numerous than the females with each 

 higher age group. It is beUeved that this indicates that u bigger percentage of the 



