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



159 



250 



200 



- 150 



E 100- 



M J J 



Month 



A S O N D 



Figure 3 



Percent marginal increments means (-) with the minimum and maximum values 

 for the night shark (C. signatus) caught from 1995 to 1997 off northeastern Brazil 

 (n=171). The number of individuals sampled per month is shown above the ver- 

 tical bars. 



est mean values are reached (Fig. 3). These values are 

 followed by the lowest mean PMI in October, indicating 

 that the new translucent zone forms from that point on. 

 Monthly PMIs showed significant differences throughout 

 the year (P=0.0463) and post-hoc comparisons detected 

 differences in February, April, September, and October. 

 Furthermore, monthly categorization of vertebral edges 

 indicated that the highest frequency of broad light edges 

 (MI 0.6-1) appears from July through December and nar- 

 row dark edges (MI 0) from March through December, 

 with the exception for months of May and August (Fig. 4). 

 Trimonthly frequency distribution of absolute marginal in- 

 crements (Mis) was carried out for juveniles, revealing four 

 and five bands, and for adults, revealing more than eight 

 bands. For the former group, a higher number of broader 



increments and fully formed bands in the third and fourth 

 trimesters were observed (Fig. 5). For adults, an unclear 

 pattern was observerd perhaps because a smaller sample 

 size was obtained. 



Because there was no complete agreement on the time 

 of band formation among different MI analysis for juve- 

 niles and adults, age was assigned by assuming an annual 

 pattern of band deposition. The birth mark present in all 

 analyzed vertebrae was not taken into account for age as- 

 signation. Under this assumption, band counts indicate 

 relative age (years). 



Mean observed lengths-at-age were higher than mean 

 back-calculated lengths for males and females and were 

 likely due to the strong variation in size for each age class 

 (Table 1). The tendency of back-calculated lengths of older 



