560 



Fishery Bulletin 92(3). 1994 



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Figure 4 



Mean monthly otolith marginal increments for weakfish, 

 Cynoscion regalis, ages 1-6 from the Chesapeake Bay region, 

 1989-91. Vertical bars are ± one standard error. Numbers 

 above the bars represent sample size. 



The number of presumed annual marks on otolith 

 sections agreed poorly with those on other hardparts 

 (Fig. 3). Scale and otolith readings agreed only 27% 

 of the time (Table 1) and scales consistently had one 

 less mark than otoliths (26 out of 45). Pectoral and 

 dorsal rays showed better agreement with otoliths 

 than with scales, 49% and 46% respectively. 



Validation of the otolith method 



Opaque bands are laid down on otoliths once a year 

 in the spring. Mean monthly marginal increment 

 plots for ages 1-6 showed only one trough during the 

 year, indicating only one opaque band was formed 

 per year (Fig. 4). A few fish began to lay down annuli 

 in March, as shown by the decrease in mean mar- 

 ginal increment and a relatively high variation in 



marginal increment size. However, lowest marginal 

 increment values occurred in April and May, indi- 

 cating most fish formed annuli during these months. 

 Greatest otolith growth occurred during the months 

 of June, July, August, and September, as demon- 

 strated by the step-wise increase in mean marginal 

 increments. By October, mean marginal increments 

 reached a fairly stable maximum, indicating little or 

 no otolith growth. This maximum continued until the 

 next March or April, when annuli were again laid 

 down. 



Because of the scarcity of older fish, it was not pos- 

 sible to validate conclusively fish older than age 5 by 

 separate marginal increment plots. However, there 

 was no evidence that the pattern of annulus forma- 

 tion changed within the weakfish lifespan. Annuli 

 were consistently formed during March-May for fish 

 of different sizes, sexes, and ages (1—6), and otoliths 

 did not form more than one mark per year even 

 though these ages represented various stages in the 



