Ferreira and Vooren: Age, growth, and structure of vertebra in Galeorhinus galeus 



21 



h.a. 



B 



Figure 1 



Drawings of Galeorhinus galeus vertebrae showing patterns of calcification in centra. (A) View from end of centrum toward focus, 

 showing growth rings; (B) view at center of centrum, showing Maltese Cross of calcified radialia; (C) longitudinal view showing double 

 cones and growth rings, c = centrum, h.a. = haemal arch, i = intermedialia, n.a. = neural arch. 



slopes of the regression lines tested (Sokal and Rohlf 

 1981). As they were found to be different, a power rela- 

 tionship was fitted to TL x centrum radius for each 

 sex. Each ring was measured and these values inserted 

 into the power equation to back-calculate the length 

 of each shark at formation of the respective ring. The 

 von Bertalanffy growth model was fitted to the mean 

 lengths-at-age, using the methods of Ford and Bever- 

 ton as cited by Gulland (1977). 



Results 



Size composition 



School sharks were present in the study area from 

 April to November. During April and May all captured 

 individuals were adolescent or adult gravid females 

 (Fig. 2). From June to September the largest captures 

 were registered (Table 1) and individuals from both 

 sexes and all sizes (43-148 cm) were present (Figs. 2, 

 3). Larger juveniles were still captured during Sep- 

 tember, but individuals smaller than 70cm TL were 

 caught only from June to August. 



A size variation within the sample size composition 

 was also observed when analyzing the length frequen- 

 cies plotted by cruise (Figs. 4, 5). Some size classes 

 were better sampled during certain cruises. For in- 

 stance, the sample was mainly composed of adults 

 during cruises 3/80, 7/80, and 4/86, and of juveniles 



