108 



Fishery Bulletin 93(1). 1995 



"l-5-i l erythropterus 



6 8 10 



Number of rings 



Figure 2 



The relationship between otolith weight and 

 the number of rings counted in whole otoliths 

 of (A) L. erythropterus, (B) L. malabaricus, 

 and (C)L. sebae. 



(P<0.05). Under the assumption of a constant mass 

 growth model, radiometric age estimates were again 

 most similar to those found for whole otolith ring 

 counts. The match was best for samples of cored 

 otoliths (2489, 2490) where assumption of a mass 

 growth model is almost absent (Table 2). 



Lutjanus sebae — The specific activity of 226 Ra and the 

 210 Pb/ 226 Ra activity ratio varied less between samples 

 in L. sebae than in the other species (Tables 1 and 2). 

 As with the other species, otolith weight was linearly 

 related to the ring counts of whole otoliths; therefore, a 



single constant growth rate was assumed in interpre- 

 tation of the radiometric data (Fig. 2C). The radiomet- 

 ric age estimates of intact otolith samples of juveniles 

 (2068, 2069, 2070), based on the assumption of no 

 allogenic 210 Pb uptake in the otoliths (R=0.0), were 

 higher than the ring counts for both sectioned and whole 

 otoliths (Table 2). Samples 2068 and 2069 were prob- 

 ably subject to high rates of allogenic 210 Pb uptake, as 

 indicated by the high stable Pb/Ba mass ratios (Table 

 1). Radiometric ages of both sets of cored otoliths were 

 most similar to the age estimates based on whole otolith 

 counts. However, both these samples (2647 and 2648) 

 had very low stable Pb/Ba mass ratios (Table 1). Mod- 

 elled radiometric ages of L. sebae samples (both whole 

 and cored) for different values of R indicate that R - 0. 10 

 best matches the ring count of whole otoliths (Table 3). 



Lead.'Barium ratios 



The stable lead:barium ratios of all samples were 

 plotted against radiometric age assuming an initial 

 activity ratio/? = 0.0 (Fig. 3). Neither L. malabaricus 

 nor L. erythropterus showed an increase in the ratio 

 with increasing age. However, in four of the five L. 

 sebae samples radiometric age increased rapidly with 

 increasing stable lead (Fig. 3). 



Otolith ageing 



Lutjanus erythropterus — The growth curves of L. 

 erythropterus based on ring counts in whole otoliths 



