336 BULLETIN OF THE BUREAU OF FISHERIES 



for any further inci'ease in the width of this zone in older age groups. In fact, the 

 average of the third year scale increments should probably decrease in the 5-year 

 fish. (See below.) The data of Table 22 show that tiiis average usually increases in 

 the 4-year fish and varies little with the older age groups. 



As we assumed was the case in the mature 3-year fish, so, we maj^ believe, must 

 the mature 4-year herring have been retarded in their growth rate by sexual matur- 

 ation. This retardation in the growth of the mature 4-year fish would permit the 

 slower growing immature individuals of the same age and year class to approach 

 closely the growth rate of the mature, to equal it, or to exceed it. These immature 

 4-year individuals when joining, in the following year, the mature 5-year fish would 

 tend to raise the average scale increment of the fourth year of these fish, so that it 

 would approach more closely that of the captured matiu-e 4-year fish of the same 

 year class, equal it, or exceed it. The larger fourth-year scale increments in all the 

 5-year groups, when compared with corresponding increments of the 4-year group 

 (Table 22), seem to indicate that retardation in the growth of the 4-year fish is always 

 so great that the immature 4-year fish when in theii- fifth year are able to increase 

 the fourth year scale increment of the fifth age group considerably above that of the 

 fourth age group of the same year class. 



However, as explained elsewhere (p. 334), inasmuch as the sixth age group of a 

 year class is composed v/holly of the surviving mature members of the fifth, the scale 

 increments of these two age groups of a year class ought to be the same in corre- 

 sponding years. The 6-year fish did not seem to be represented adequately in the 

 various year classes to permit a definite statement as to the presence or absence of 

 Lee's "phenomenon" in the sixth age group (p. 334). They gave inconsistent results. 

 It is a question, therefore, whether the sixth age group should be considered in the 

 present discussion. If considered, it is at once apparent that the tendencies that 

 exist in the scale and computed growth (Talkie 23) increments of the younger age 

 groups continue into the sixth. The scale and body increments of the first two years 

 of life continue their decrease in this age group, while those of the fourth and fifth 

 years continue their increase. The 6-year fish agree in these characteristics — con- 

 trary to what was stated on page 334, they are here consistent. If the data of Tables 

 22 and 23 of the 6-ycar fish are valid, we are unable, on the basis of the two assumptions 

 considered above, to account for the continued decrease and increase in the growth 

 increments in the sixth age group. 



Another apparent discrepancy appears in the increment data of Tables 22 and 

 23. The progressive decrease in the increments of the first and second years of life 

 with age was explained by assiuning that the third age group included the fast-grow- 

 ing individuals of the year class, the fourth the surviving, fast-growing mature 3-year 

 fish and the more slowly growing individuals that reach sexual maturity in the fourth 

 year, and the fifth age group the surviving, mature 4-year fish and the most slowly 

 growing individuals of the year class that reach sexual maturity in the fifth year. 

 Obviously, we should expect the average third year increment (scale and body) of the 

 5-year fish (also of the 6) to be less than that of the faster growing 4-year group of 

 the same year class; but Tables 22 and 23 show it to be the same, less, or greater. 



Is probably another factor uivolved? The only other plausible factor that I can 

 suggest at pr,esent is the "law of compensation in growth" developed by Gilbert 



