382 



BULLETIN OF THE BUREAU OF FISHERIES 



table suggest that, in general, the males become relativ^ely more numerous than the 

 females with each higher age group (45.5 to 46.2 to 50.4 to 50.5 to 54.8 to 57.9 per 

 cent). Tliis increasing relative abundance of the males with increasing age indicates 

 that the females of a year class are captured earlier in life than the males. This 

 appears to be substantiated by the data of Table 49, in which the percentages are 

 arranged according to the year class to which the herring belong.^ From this table 

 it may be seen that when the averages are based on more than 15 specimens, the per- 

 centage, with one exception (5 of 1918), of the males increases while that of the 

 females decreases with age. The percentages of the 6 and 7 year fish of 1917 and of 

 the 6-year fish of 1918 are based on too few specimens to be reliable. This early 

 reduction in number of the females of a year class can not be due to the selective 

 effect of the pound nets, as the pots of these nets have such a small mesh (2 J^ to 2 3^ 

 inches, stretched mesh) that all adult herring that get into these pots are retained bj' 

 them. The only other explanation seems to be that a bigger percentage of the 

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

 the third year; that is, the females matm-e earlier in life than the males, and that con- 

 sequently more males than females matm-e for the first time in the fourth and probably 

 fifth years. If this is true, the percentage of the relative abundance of the males of a 

 year class should show a big increase in the fourth age group and should then either 

 remain approximately constant or perhaps show a slight increase in the older age 

 groups. The facts seem to evidence the truth of this theoretical conclusion. The 

 percentage of the males (Table 49) increased 11.6 and 12.2 per cent in the fourth 

 age gi-oup but decreased 6.5 per cent in the 1918 year class and increased 5.2 per 

 cent in the 1919 year class in the fifth age group. 



Table 49. — Relative abundance of males and females in different age groups of various year classes of 



Bay City herring ' 



I The number in parentheses indicates the total number (male and female) employed. 



RELATIVE ABUNDANCE OF SEXUALLY IMMATURE AND MATURE HERRING IN THE 

 SAMPLES AND IN THE GENERAL POPULATION 



In sexually immature herring the testes and ovaries consist of narrow, thin, flat 

 strands of soft, whitish material and extend from the anterior to the posterior end of 

 the body cavity along its dorsal wall. In the females the ovaries may contain minute 

 eggs visible to the naked eye. When such a condition exists in a large individual at 

 spawning time it is problematical whether the individual is actually sexually immature 

 or whether it is simply a nonspawning mature fish; that is, a fish that had spawned 

 before but which for some reason had failed to develop its sex products in the year of 

 its capture. In a sexually mature herring the sex pro(iucts are in an advanced stage of 

 development; both the testes and ovaries are enlarged and partly fill the body cavity. 



' The 1924 samples are not included in Table 49 becatt^e, having bean taken late in the season, they are not comparable in this 

 respect with the samples of the preceding years, which were taken relatively early in the season. 



