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



163 



in the present study is similar to the 

 outcome for C. limbatus older than 

 four years (Wintrier and Cliff, 1996). 

 For the last mentioned species, the 

 problem was circumvented by 

 restricting MI analysis to juveniles 

 (Killam and Parsons, 1989). 



Age was assigned by assuming 

 an annual pattern of deposition, as 

 commonly occurs for most carcha- 

 rhinids like C. brevipinna and C. 

 limbatus, Rhizoprionodon terraeno- 

 vae (Branstetter et al., 1987; Brans- 

 tetter and Stiles, 1987), Negaprion 

 brevirostris (Gruber and Stout, 

 1983), and C. longimanus (Seki et 

 al, 1998; Lessa et al., 1999c). Three 

 sources of bias generally occur with 

 MI analysis: 1) sample sizes are 

 small for any particular month or 

 for any age class (Cailliet, 1990); 2) 

 data are collected over a too long 

 a period causing variability on ac- 

 count of annual marks that are not 

 formed at the same time ( Brothers, 

 1983 ) and 3 ) births occur over a long 

 period (Brothers, 1983). All these 

 may have biased MI analysis in the 

 present study. 



Research carried out in the study 

 area by Hazin et al. (2000) indi- 

 cated that copulation takes places 

 throughout the austral summer. 

 Embryos measuring 10 to 40 cm 

 were collected in February, whereas 

 31.8 to 37.2 cm embryos were found 

 in June. This remarkable variability 

 in embryo size during the gestation 

 period suggests that birth period 

 lasts several months. Furthermore, 

 with an estimated back-calculated 

 birth length of 66.8 cm, individuals 

 measuring -40 cm in February will 

 be born long before individuals that 

 measured 37.2 cm in June. Such a 

 protracted parturition period could 

 lead to differences in MI of the same 

 cohort. Thus, after an assumed -12 

 months gestation period, individu- 

 als are born with birth dates vary- 

 ing by several months. Moreover, 

 no significant differences in MI 

 analysis was found for C. porosus 

 and /. oxyrhynchus, which also have 

 a protracted birth seasons (Lessa et 

 al., 1999a, 1999b). 



A comparison of growth model 

 parameters by using known size 

 information, such as size-at-birth 

 and maximum observed size, can be 



