Fishery Bulletin 92(1). 1994 



the core, the first annulus is sometimes difficult to 

 identify. Subsequent annuli are represented by eas- 

 ily identified, narrow, opaque bands that alternate 

 with wider translucent bands outside the proximal 

 margin of the first annulus (Fig. 1). 



Annuli are formed on otoliths once a year in the 

 period April-May. For ages 1-7, mean monthly 

 marginal increment plots show only one minima 



during the year, indicating that only one annulus is 

 formed each year (Fig. 2). The trough starts abruptly 

 in April, a period when there is, in general, maxi- 

 mum variation in the mean marginal increment, 

 suggesting that some fish have begun to form the 

 annulus while others have not. Lowest marginal 

 increment values occurred in May, the most inten- 

 sive period of annulus formation. Marginal incre- 



E 

 E 



c 



CD 



E 



CD 

 CJ 



c 



~co 

 c 



en 



ca 



18 •' ,6 



ft* 



Age 1 



jsJ 



Age 2 



) I! 



1 



JFMAMJ JASOND 



Age 7 



nnn 



Age 8 



H 



JFMAMJJASOND 



Months 



Figure 2 



Mean monthly marginal increment for Atlantic croaker ages 1-8 from the Chesa- 

 peake Bay region, 1988-91. Vertical bars are ±1 standard error. Numbers above 

 the bars are sample sizes. 



