204 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



i |  i i | ' ' ' I ' ' 



I 



MALES 



-.-r-t'l . I I 



I . . . I 



FEMALES 



•  I ST QUARTER 



• '2D QUARTER 



, . 3D QUARTER 



• 4TH QUARTER 



j-i--i"i i i I i i i I i i i I i i i 1 i i i I 



WEIGHTED MEAN 

 OF BOTH SEXES 



,'V 



, I . 



I I . 



' ' '  ' 



J-L 



12341 234 I 2341 23412341 23412341234 

 12 3 4 5 6 7+ 



AGE - YEARS AND QUARTERS 



Figure 18. — Growth in weight of yellowtail from the 

 southern New England stock caught during different 

 calendar quarters. Dashed line indicates probable 

 growth during early life. 



from certain characteristics of the data. There is 

 little doubt that the average weight of the yellow- 

 tail taken during the third year of life (2-annuli) 

 is greater than the average weight of the fish re- 

 maining in the sea, because the fishery selects fish 

 above a certain size. We shall note subsequently 

 that growth during the first year of life is very 

 small, as suggested by the dotted lines in figure 

 18. At the other end of the curve we have com- 

 bined the 6-annuli and older fish in the first quar- 

 ter and 7-annuli and older fish in other quarters. 

 This combination of age groups is probably re- 



Table 27. — Mean weights and growth rates of yellowtail, by 

 quarter, age, and sex, from the southern New England 

 stock, 1942-47 



SUMMARY 



Mean instan- 

 taneous growth 

 Age groups: rate 



1-2 annuli 0.673 



2-3 annuli 291 



3-4annuli 233 



4-5 annuli 238 



5-6 annuli .206 



6-7 annuli . 173 



sponsible for the greater growth among females 

 in the first and fourth quarters. 



The mean growth rate, computed from the data 

 in table 27, will be of use to us later in population 

 studies. Such a mean should be representative if 

 we give proper consideration to differences be- 

 tween the sexes and among quarters, because we 

 found no trends in the growth rate during the 

 period of our study. The estimated weights for 

 each sex in each quarter have been combined in 

 quarterly averages through weighting the means 

 of the sexes combined by the number of each sex 

 in the scale samples at each age from 1943 

 through 1947. We then computed the instan- 

 taneous growth rate (k) for each age in the four 

 quarters from the formula 



e" = l + b 

 in which b is the fractional increase in weight 

 over that at the beginning of the year (after 



