Lowerre-Barbieri et al.: A comparison of otolith and scale ageing methods for Cynoscion regalis 



563 



E 

 E 



c 

 .o 



Age (years) 



Figure 7 



Mean weakfish, Cynoscion regalis, size at age: (A) 

 based on scales and (B) based on otoliths. Vertical 

 bars are ± one standard error. Numbers above the 

 bars represent sample size. 



^9 



c 



CD 



E 



CD 

 O 



c 



Id 



c 



E? 

 co 



E 

 > 



■4— ' 



_ca 



CD 



Apr May Jun Jul Aug Sep Oct 



Scales 



ay 



2/ 





T 



Apr May Jun Jul Aug Sep Oct 



Month 



Figure 8 



Mean monthly relative increments for weakfish, 

 Cynoscion regalis, scales and otoliths. Vertical bars 

 are ± one standard error. Numbers above the bars 

 represent sample sizes. 



second annuli, whereas scales had a very small in- 

 crement between these annuli. The largest scale 

 growth increment after age 1 was between annuli 3 

 and 4. Neither hardpart showed a consistently de- 

 creasing mean annual growth increment as age in- 

 creased. Although this assumption is often included 

 in scale-reading criteria, it would be inappropriate 

 for weakfish. 



Back-calculated mean body sizes at age were larger 

 for scales than for otoliths (Table 3). In part, this 

 discrepancy may reflect different times of annulus 

 formation: back-calculated lengths from scales, in 

 general, estimate sizes in August, whereas back-cal- 

 culated lengths from otoliths estimate sizes in April 

 and May. Also, at older ages, back-calculated body 



sizes at age based on scales would be expected to be 

 larger because of the underageing of older fish by scales. 

 Both scales and otoliths showed smaller back-cal- 

 culated mean body size at age 1 than observed. At 

 later ages, back-calculated TL's from scales were 

 larger than observed, while back-calculated TL's from 

 otoliths showed no consistent trend (Table 3). The 

 cause of the smaller back-calculated TL's at age 1, 

 however, did not appear related to Lee's phenomenon, 

 as there was no consistent trend of smaller age-1 an- 

 nular radii at older ages at capture (Tables 4 and 5). In 

 fact, the largest mean SAR and OAR at age 1 came 

 from 5-year-old fish. However, age-1 OAR's from the 

 oldest fish in the study (>age 6, n=5) were distinctly 

 smaller than those observed in younger fish. 



