Natanson et al.: Age and growth estimates for Carcharhinus obscurus 



121 



Eight of these fish were at liberty from 10.1 to 15.8 

 years. Estimated ages at tagging were based on the 

 vertebral growth curve and ranged from birth to 27 

 years. The best example of longevity came from a 

 dusky shark that was tagged at an estimated 27 years 

 (260 cm FL) and was recaptured 12 years later at an 

 estimated age of 39 years (Table 5). 



Discussion 



In the present study, vertebral data and length-fre- 



quency data were independently analyzed to derive 

 estimates of von Bertalanffy growth parameters for 

 the dusky shark. Because of the differences between 

 the methods and their sensitivity to the data used to 

 calculate the VBGF parameters, each method pro- 

 duced slightly different growth curves and, therefore, 

 different estimates of age at maturity and longevity 

 (calculated based on maximum reported size). The 

 length-frequency estimates obtained from the dusky 

 shark data are probably somewhat biased owing to 

 limitations of the data and properties of the length- 

 frequency model (Majkowski et al., 1987; Shepherd 



