Skomal and Natanson: Age and growth of Prionace glauca 



631 



Tagging data 



A total of 43 blue sharks was recaptured with sufficient 

 information for tag-recapture analysis. Data from 18 

 sharks at liberty >0.9 years were used for Gulland and 

 Holts (1959) method and all the recaptured sharks were 

 used for the Francis ( 1988a) method (GROTAG). 



The results of the likelihood ratio tests with GROTAG 

 (Francis, 1988a) showed that the more complex nonlinear 

 model with all six parameters was the best fit for these data 

 (Table 3, model 3). The mean annual growth rates are ggg = 

 44.2 cm/yr and gjg^ = 25.5 cm/yr, corresponding to growth 

 rates at a FL= 90 cm and 180 cm, respectively (Fig. 7). Von 



Bertalanffy estimates from the Gulland and Holt (1959) 

 and GROTAG (Francis, 1988a) methods produced similar 

 von Bertalanffy curves (Table 4, Fig. 8A). 



Longevity 



The maximum age determined from vertebral band pair 

 counts was 16 and 15 years for males and females, respec- 

 tively. These ages are likely to be an underestimate of 

 longevity, given the history of fisheries exploitation of this 

 species. Using Taylor's (1958) method, we determined that 

 the age at which 95% and 99% of the L^ is reached was 

 16.5 and 26.1 years, respectively. Fabens (1965) method for 

 >99% longevity produced an estimate of 20.7 years. 



