334 BULLETIN OF THE BUREAU OF FISHERIES 



this be true the younger age groups contain a larger proportion of fast-growing fish 

 than do the older groups, and the "annular" diameter measurements of theii scales 

 give higher values. In my r'iscussion of the data of Table 30, on page 384, I state 

 that most herring attain sexual maturity in the third and fourth years of life, and 

 that in relatively few is the first spawning delayed until the fifth year. It is possible 

 that the herring that spawn in their third year are the bigger individuals of their 

 year class, and that those that do not spawn until their fourth or fifth year are 

 smaller. Some evidence that this is true may be found on page 390, where I show 

 for the third and fourth age groups of the Oscoda herring that the immature individ- 

 uals of an age group average less in length than the sexually mature. The influx 

 of the smaller individuals into the fourth and fifth age groups would presum- 

 ably tend to lower the average "annular" diameter measurements of these age 

 groups as well as their average actual measured body lengths. The average lengths 

 of the "annular" scale diameters would then be less for all corresponding years of 

 life in the 4 and 5 year fish than in the 3-year fish, and similarly they would, in general, 

 be less in the 5-year fish than in the 4. It is assumed here that the number of fish 

 that reach sexual matiu'ity in the fourth or fifth year is large enough to alter the 

 average giowth rate of their respective age group. Otherwise the corresponding 

 scale diameters should be approximately the same in the three age groups under con- 

 sideration. However, the 6-year and older fish of a year class composed wholly of 

 the surviving mature 5-year individuals ought to show, for the same years of life, 

 scale-diameter measurements similar to those of the 5-year group. Lee's "phenom- 

 enon," if conditioned wholly by the growth-rate composition of the age groups, 

 should not be present in the scale diameter measurements of the fifth and older age 

 groups of the same year class. These age groups should have identical growth-rate 

 compositions. 



An examination of the total length values of scales given in Table 22 shows that 

 these data agree fairly well with the above theoretical deductions derived from 

 Lee's first suggestion, in so far as the interrelations of the scale measurements of the 

 tlurd, fourth, and fifth age groups are concerned. In general, the scale diameters 

 of these three age groups decrease in length with age in each year class; but whether 

 Lee's "phenomenon" is absent from the scale-diameter measurements of the fifth 

 and older age groups of a year class is not so evident. No data are given in Table 22 

 for the 7-year fish, while the sixth age group is represented there by 7 individuals 

 of the 1918 year class and by 18 individuals of the 1919 year class. These age groups 

 are somewhat better represented in the table (35) of computed body lengths. Even 

 here the 7-year fish are too sparsely represented to permit a comparison of their 

 calculated lengths with those of the 5 and 6 year groups of the same year class, wliile 

 the sixth age group, though better represented, still comprises comparatively few 

 individuals. Notwithstanding these small numbers, Table 35 shows that the com- 

 puted lengths of the 6-year fish of the 1917 year class nearly coincide with the corre- 

 sponding lengths of the 5-year fish of that year class in all years, while the calculated 

 lengths of the 6-year group of the 1918 year class agree fairly well with the corre- 

 sponding lengths of the 5-year fish of that year class; Lee's "phenomenon," if present 

 at all, is certainly not very prominent in the computed lengths of the 6 and 5 year 



