424 



Fishery Bulletin 98(2) 



o 



90 

 80 

 70 

 60 

 50 

 40 

 30 

 20 



80 120 160 



Duration (days) 



Figure 2 



The body size (fork length) of ALC-marked juvenile Atlantic men- 

 haden (Brevoortia tyrannufi I sampled during the validation rearing 

 study (upper panel! and rate of growth estimated from mean size 

 of sampled fish (lower panel i. The rates of growth are plotted at 

 midpoints between sampling periods. 



Table 1 



Results of least squares linear regression analysis for 

 marked Atlantic menhaden, Brevoortia tyrannus, otolith 

 mcrement counts (n=34, r-=0.984, and SE=standard error). 



Parameter 



Estimate 



SE 



Slope 



Power' 



Intercept 



1.0048 

 99.1''^ 

 0.3771 



0.0224 



1.8257 



0.168 



0.162 



' Statistical power to detect a deviation of 0.1 in the estimate of 

 the slope at the P=0,0.5 level. 



(Fig. 1). Even though growth rate decHned to low 

 levels during initial study weeks, especially for the 

 high-salinity group (Fig. 2), an otolith increment 

 continued to be formed daily even when increment 



widths fell below 1 pm for a number of days (Fig. 

 3). If a difference in increment formation rate had 

 occurred between groups, we would not have been 

 able to determine the cause because both tempera- 

 ture and salinity varied between groups. It seems 

 likely that the faster growing fish responded to the 

 higher temperatures. Regardless, both test groups 

 experienced conditions that could be expected in 

 the field during winter. The October-spawned larval 

 menhaden used in our study displayed a growth 

 increment mean width that ranged from values that 

 were greater than those previously measured at sea 

 to those that were less than previously measured in 

 estuaries in a relatively short period of days (com- 

 pare with Fitzhugh, et al. 1997). 



The rearing conditions for specimens maintained 

 during our study and earlier studies ( Ahrenholz et al., 

 1995) should provide otolith increment validations 

 for most, if not all, Atlantic menhaden that recruit 



