26 



Fishery Bulletin 89(1), 1991 



Q opaque 

  translucent 



IujmW 



tfUnlftm, 



Figure 12 



Widths (m.u. = 10~ 3 cm) of translucent and opaque zones 

 distributed by ring for female Galeorhinus galeus (134 cm TL, 

 29 yrs-old). 



in width. Females have the same general pattern, but 

 some variation in width still can be detected after the 

 15th ring has been formed (Fig. 14). 



From June to September, 91% of the vertebrae ex- 

 amined showed more calcified zones forming at the 

 margins (Fig. 15). During June this percentage was 

 80%, rising to 100% during July and falling to 75% in 

 September. The vertebrae observed with less calcified 



a f 



w.o.z. (m.u.) 



Figure 14 



Frequency distribution of widths of opaque zones after the 

 15th ring for female and male Galeorhinus galeus. 



120 



a>100 



c 



o 



~ 80 



is 



c 



o> 60 



40 



g. 2 



I 



 pre-ring 



O ring 



^ post-ring 



m& 



JUN 



JUL AUG 



months 



SEP 



Figure 15 



Percentage of type of marginal zone in vertebrae of Galeo- 

 rhinus galeus observed June-September (n = 82). 



zones at margins during June (20%) were of the pre- 

 ring type (wide less-calcified zone), and the ones ob- 

 served during September (25%) were of the post-ring 

 type (narrow less-calcified zone). These results indi- 

 cated that the ring formation probably occurred during 

 the winter months (June to September). One mark per 

 year seems to be the most likely case for the school 

 shark, and results here reflect this assumption. 



In vertebrae of embryos at 8 months of intrauterine 

 age, only the cartilage of cones was mineralized and 

 no rings were visible (Fig. 16). Their intermedialia was 



