20 



Fishery Bulletin 89(1), 1991 



region under the first dorsal fin. The 

 vertebrae were cleaned, frozen, and pre- 

 served in 70% ethanol. Several tech- 

 niques were tried to aid enhancement and 

 interpretation of the vertebral rings. 

 Vertebrae of 10 sharks were sectioned 

 into two halves, through transverse or 

 sagittal planes, and the exposed faces 

 were polished on wet 600-grit sandpaper. 

 They were decalcified in 1% formic acid 

 for 1 hour, rinsed in running water for - 

 24 hours, dried and stained with graphite 

 powder. The material was observed with 

 a dissection microscope at 10 x magnifi- 

 cation using reflected light. 



Vertebrae from 82 individuals (35 

 males, 45 females, and 2 embryos) were 

 dehydrated in ethanol, cleared in styrene, 

 embedded in polyester resin, sectioned 

 with a jeweller's saw in transverse and 

 sagittal planes, and polished on wet 400- 

 grit sandpaper to obtain slices of 50-250 

 microns. Radiographs of all sections were 

 taken with Soft X-ray equipment by 

 Moureuil (France), at settings of 10-30 

 kV, 5-15 mA, and exposure times of 3-5 

 minutes. Kodak Industrex M radiography 

 film was used. The radiographs were 

 mounted on glass slides as were vertebra 

 sections, either directly or after staining 

 with Harris's haematoxylin or basic fuch- 

 sin. Vertebrae from five sharks were 

 prepared and sectioned by standard histo- 

 logical techniques for calcified material. Sections were 

 stained with Sudan 4 for observation of the lipid con- 

 tents of cells. 



A dissecting microscope at 10 x magnification was 

 used for measuring and counting growth rings, and a 

 compound microscope at 100 x magnification for obser- 

 vation of cell structure and details of the margin of the 

 vertebra. The criteria to define a ring requires that it 

 must occupy a distinct translucent zone relative to ad- 

 jacent opaque zones and that the ring traverse the cor- 

 pus calcareum and intermedialia (modified from Casey 

 et al. 1985). 



Measurements of growth increments were made with 

 an ocular micrometer positioned to measure distances 

 from the focus (notochordal remnant) to successive 

 growth bands. The radius of each centrum was mea- 

 sured from the focus to the distal margin of the corpus 

 calcareum (Fig. 1). The widths of individual translucent 

 and opaque zones were measured in the microradio- 

 graphs of 10 individuals. The periodicity of the forma- 

 tion of the rings was studied by examining the margins 

 of the vertebrae collected from June to September. The 



marginal zone was classified into three types: pre-ring, 

 consisting of a wide, less calcified zone; ring, consisting 

 of a more calcified zone; and post-ring, consisting of 

 a narrow, less calcified zone. Measurements of mar- 

 ginal increments were considered to be ineffective 

 because the widths of zones varied greatly between size 

 classes. 



A linear regression of TL as a function of centrum 

 radius was fitted to the data for juveniles and adults 

 (sexes combined and separate) and the equality of 



