384 BULLETIN OF THE BUREAU OF FISHERIES 



As a rule, in a long-lived species of fish the year of age at whicli sexual maturity is 

 first attained varies more and has a greater range than in a short-lived species. Thus, 

 Thompson (1914) found that about 5 per cent of the 7-year female hahbut of the Pacific 

 were sexually mature and that at 12 years of age 50 per cent were mature, while at 15 

 years 10 per cent were still immature. In my herring samples 94.2 per cent of the fish 

 in their third year, 98.2 per cent in their fourth year, 99.2 per cent in their fifth year, 

 and all older fish were sexually mature. Thus, many of the relatively short-Hved 

 Bay City lake herring reach maturity in the third year. Fourteen 2-year fish were 

 taken in my samples. This number is too small to show the percentage of fish that 

 reach sexual maturity in their second year. It indicates, however, that a few fish do 

 so mature and join the schools of breeding fish in this year. A small percentage (0.8) 

 of herring is still sexually immature or at least nonspawning in the fifth year. In the 

 sample of 1923 no immature herring are present in the fourth and older age groups. 



It should be emphasized that because the collections were made during the 

 spawning run, the percentages of Table 50 do not show the actual proportion of mature 

 and immature individuals in the general population in all age groups. They show 

 these proportions only for the fish that take part in the spawning nm. In this run 

 only about 6 per cent of the 3-year fish were immature. Inspection of Table 30 

 shows that the percentage of immature herring of the third year must have been 

 much larger than this. It there appears that the fourth age group predominates 

 in each sample for four consecutive years. This can not be due to selective action 

 of the pound nets on fish of the 4-year lengths, for these differ in length by only about 

 7 millimeters (Table 34) from the 3 and 5 year fish. If we assume that the 3 

 and 4 year fish captured in 1921 were in all respects representative samples of the 

 general population and that there is no selective death rate, they should have reap- 

 peared as 4 and 5 year fish in the catch of 1922 in the same proportion as they occurred 

 as 3 and 4 year fish in that of 1921 . In that case the 5-year class of 1922 would have 

 been larger than the 4-year class. It is, in fact, much smaller. It seems, then, that 

 before the 3-year fish of the spawning run of 1921 entered the run of 1922 their number 

 was greatly augmented. That is, many immature fish from the general population 

 of the 3-year class of 1921 were added to the spawning run of 1922 as mature 4-year 

 fish. It is this annual addition that results in the predominance of the 4-year fish 

 in the samples of all years. As fewer fish attain sexual maturity for the first time in 

 their fifth year than in their fourth, the 5-year group would be composed chiefly of 

 fish that escaped the nets or death from other causes in their fourth year, and this would 

 then result in the consistant smaller representation of the 5-year group each year. 

 That some individuals attain sexual maturity for the first time in their fifth year 

 seems probable from the fact that the 4 and 5 year herring do not reappear as 5 and 

 6 year fish, respectively, in the same relative abvmdance. Unless we postulate, as 

 we did with the 3 and 4 year fish, that the 5-year class is augmented by individuals 

 that were sexually immature in their fourth year, we can hardly explain why the 4- 

 year fish are, on the average, about twice (2.2 times) as abundant as the 5-year fish, 

 but when reappearing as 5-year indi\'iduals the former are about seven times as 

 abundant as the latter, which reappear as 6-year fish. (Compare the number of 

 individuals of the lower half of Table 30.) Table 30 shows, further, that the 5 and 

 6 year fish reappear as 6 and 7 year fish, respectively, in approximately the same rela- 

 tive abimdance, which indicates that virtually no herring reach sexual maturity for the 

 first time in the sixth year of fife. (The general conclusion that the percentage of imma- 



