FISHERY BULLETIN: VOL. 81. NO. 1 



04 - 



03 - 



02 - 



03 - 



02 



01 



Age 3 



Slope =0.002608 



Slope =0.002010 



M-t// ? // 



e ^?-^ 



J I u I 



Age 2 



Slope = 0002695 



Slope =0002140 



,^H' : 



// r // 



10 20 

 JUNE 



30 10 20 30 

 JULY 



10 20 

 AUG 



30 



10 7 4 



SEPT OCT NOV 



Figure 3.— Seasonal growth of the scale margin beyond the 

 1976 annulus in Atlantic menhaden collected from Narragan- 

 sett Bay during 1976. Means ±95% confidence limits are 

 shown. Curves depict the instantaneous daily growth of the 

 scale margin (Table 4, Equations (5)-(8)). 



Growth rates in fork length and wet weight 

 were determined by regressing log e fork length 

 and log? wet weight vs. the date of capture (Figs. 

 1, 2; equations are in Table 4). Mean instantane- 

 ous daily growth rates were equal to the slopes of 

 the relationships. Growth of the scale margin 

 was determined for each fish from 



G = log — 

 e S. 



(4) 



where G = instantaneous growth increment 



S r = total width (mm) of the scale at time 

 of capture 



Si = width (mm) to the most recent (1976) 

 annular ring. 



The value of G provides an independent estimate 

 of the total amount of growth by that fish during 

 1976, up to the time of capture. If the exact date 

 were known when fish resumed growth during 

 the spring of 1976, the mean daily growth rate 

 for the entire season could be determined for 

 each individual fish. However, since this date is 

 unknown, the mean daily growth rate can be 

 estimated only for the overall population, by re- 

 peatedly sampling that population and regress- 

 ing the individual values of G against the date of 

 capture (Fig. 3). This approach is analogous to 

 that already described for estimating daily 

 growth in fork length and wet weight. 



Instantaneous daily growth rates of age 2 and 

 age 3 menhaden caught within the bay during 3 

 August- 1 September were 0.27 and 0.26%/d in 

 the growth of the scale margin, 0.22 and 0.21%/d 

 growth in fork length, and 1.03 and 0.93%/d 

 growth in wet weight (Table 4). There were no 

 significant differences (F<0.05) between these 

 measures of growth for age 2 and age 3 

 menhaden, probably because the two age groups 

 were very similar in size. The mean daily growth 

 rate of the scale margin did not differ signifi- 

 cantly (F<0.05) from that of fork length, 

 indicating that both grew in the same propor- 

 tion. 



Daily growth was also estimated, as described 

 above, for all fish collected between 3 June and 8 

 September (Table 4). These growth estimates 

 were lower than those derived from fish thought 

 to have remained within the bay during August, 

 but only growth estimates in wet weight were 

 significantly different (P<0.05). 



Table 4.— Linear regressions from which the instantaneous daily growth rates of Atlantic menhaden in Narragansett Bay during 



/scale widthA 



1976 may be calculated, where jc = date of capture ( 1 June = day and 8 Sept. = day 100) and (A) y = log,( ; r— 77 l;(ti) (/-log, 



^ \ scale width,/ 



fork length ( mm); and (C) y = log, wet weight (g). y values are the means of each sample of fish; n = the number of samples. The instan- 

 taneous daily growth rate equals the slope of each regression relationship. 



138 



