NOTE Matlock et al Validation of Pogonias cromis ages 



559 



Figure 1 



Black drum scale indicating morphological features used to measure radii and annuli: A : 

 focus, B = annulus, and C = scale margin. 



The time of annulus formation was estimated by nar- 

 rowing the possible timet s) using the fish with increased 

 numbers of scale annuli. The longest period between 

 release and recapture defined the possible period of 

 formation. This estimate was refined by using the fish 

 free the next longest period, and so on. Fish with no 

 annuli increases were then used to confirm or refine 

 the possible period of annulus formation. 



The effect of tagging on scale growth was examined 

 by comparing the relationship between scale radius 

 (Y) and total length (X) and the mean distances from 

 scale focus to each annulus at release to those at re- 

 capture. Least-squares linear regression for single Y 

 at each X and analysis of covariance (Sokal and Rohlf, 

 1981) were used to compare relationships. One-way 

 analysis of variance (Sokal and Rohlf, 1981) was used 

 to compare distances from focus to each of the first 

 three annuli. The lack of scales with more than three 

 annuli at release precluded comparison of other an- 

 nuli. The probability level for all statistical analyses 

 was set at 0.05. 



Results and discussion 



The scale method for aging black drum <4 years old is 

 valid. Only one opaque zone was formed each year, 

 between April and May. Eight of the 17 fish with us- 

 able scales at release and recapture had scales with 

 more annuli (1) at recapture than at release (Table 1). 

 All fish except one (B71764) were free during May; the 

 one exception was free through 21 April. This suggests 

 that annulus formation is completed between late April 

 and late May. Data from the five fish not free during 

 April or May support this conclusion; the number of 

 annuli did not increase between release and recap- 

 ture. Two fish free for 1 day in May provided little 

 information; both showed no change in number of an- 

 nuli. Two other fish released in late April and early 

 May did not show an increase in number of annuli. 

 One fish (F31261) released in late April may have 

 formed an annulus just prior to initial capture, since 

 the second annulus was located 154 mm from the scale 

 focus, and the scale radius was 163 mm (Table 1 ). 



