FISHERY BULLETIN: VOL. 85, NO. 2 



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Galeocerdo cuvieri 



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8 10 12 14 16 



CENTRUM RADIUS 



18 20 22 24 



Figure 2.— Relationship of centrum dorsal radii to total length for Galeocerdo cuvieri taken in the Gulf of Mexico 

 and off the Virginia coast. Centrum radii measurements are in ocular micrometer units (omu). 1 omu =1.2 mm. 

 See text for discussion of the different regressions. 



Neonatal tiger sharks had only one annulus. Back 

 calculations of length at the formation of this an- 

 nulus indicated that it was formed at birth. Prebirth 

 marks, which formed at placentation (Radtke and 

 Cailliet 1984; Casey et al. 1985; Branstetter 1987c; 

 Branstetter and Stiles in press), were not found in 

 this aplacentally developing species; a condition also 

 noted for the aplacental Alopias vulpinus (Cailliet 

 et al. 1986). 



Marginal increment analysis on all but neonatal 

 tiger sharks (Fig. 3) indicated that the annuli formed 

 in late fall or early winter (October-December) be- 

 came visible off the centrum edge by January and 

 were farthest from the centrum edge in summer. 

 This "winter" annulus was consistent throughout 

 the size range of the sample (Beamish and McFar- 

 lane 1983). Therefore, the first band bordered by 

 the birth mark and the first winter annulus repre- 

 sented approximately 6 months growth; remaining 

 bands formed annually. 



Annuli along the periphery of centra in large (old) 

 tiger sharks were closely spaced, making counts for 

 these individuals more difficult. Annulus counts 

 between the two readings were identical except for 

 some of the larger individuals. In these cases, results 

 of a third count matched one of the two previous 

 counts, and this was the value accepted. 



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J ' F M" AM' J J A' S O N D 



Figure 3.— Marginal increment widths as a ratio of the width 

 of the last fully formed band in vertebral centra of Galeocerdo 

 cuvieri compared by month. Specimens from the two regional 

 samples are combined. 



The two regional samples of tiger sharks exhibited 

 similar growth rates. By combining observed length 

 at age data from both samples a single von Berta- 

 lanffy curve could be fitted by using Fabens (1965) 



272 



