Santana and Lessa: Age and growth of Carcharhinus signatus off the northeastern Brazilian coast 



161 



1 0.2 3 4 5 0.6 0.7 08 9 1 



12 

 10 - 



8 



6 



4 



2 







ill 



1 2 3 4 5 0.6 07 08 09 1 



12 

 10 



8 



6 



4 - 







3 ,d Trimester 

 n=36 



I.. I 



1 2 3 0.4 5 0.6 7 8 9 1 



12 - 



10 



4 lh Trimester 



Nihil. . 



1 2 3 4 0.5 0.6 7 08 9 1 



B 



r' Trimester 

 n= 14 



II I  - 



01 0.2 0.3 0.4 0.5 0.6 0.7 08 09 1 



12 

 10 - 



3 rd Trimester 

 n= 14 



ll 



01 0.2 03 0.4 05 0.6 0.7 0.8 09 1 



12 

 10 

 8 

 6 



4 

 2 

 



4 m Trimester 

 n=10 



Jl 



1 0.2 3 4 0.5 6 0.7 8 0.9 1 



Ml 



Figure 5 



Marginal increments (MI) by trimester for ages 4 and 5 (n = 139) (A) and a8 (Bl (n=54) for the night shark (C. 

 signatus) from northeastern Brazil. 



(Fig. 7). According to the inverted back-calculated VBGF 

 the oldest specimen in the sample was 31.7 years old (260 

 cm), whereas longevity was 31.5 years. 



Discussion 



Validating the time of band formation is considered critical 

 when using hard parts for age estimates (Brothers, 1983), 

 and validation is successful when growth zones are shown 

 to form annually in all age groups of the population (Beam- 



ish and McFarlane 1983). Marginal increment analysis, 

 carried out on younger and faster growing individuals, 

 cannot always be used for validating older age groups, and 

 therefore all ages must be ascertained (Brothers, 1983). 

 In the present study, we obtained significant differences 

 in marginal increments for the total sample. However, the 

 significance level of the test (P=0.046) was close enough 

 to 0.05 to cause us to suspect that the distributions could 

 have been similar. The time of band formation varied when 

 different age groups were analyzed separately, despite 

 suggestions that bands are completed in the third and 



