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Fishery Bulletin 97(4), 1999 



Casey and Natanson (1992) showed the advantage 

 of using tag-recapture data over vertebral analysis 

 for aging the sandbar shark. Cailliet et al. (1986) 

 reviewed the techniques available for determining 

 age and verifying age estimates in elasmobranchs. 

 They pointed out that ages estimated from growth 

 zones in calcified hard parts need to be verified with 

 other methods, such as length-frequency and tag- 

 recapture analyses. The authors also stressed the 

 importance of validating the temporal periodicity of 

 the calcified bands with tag-recapture data from the 

 laboratory or field, coupled with OTC marking. 

 Cailliet ( 1990), in an update of the Cailliet et al. 

 (1986) review, listed the studies, to that date that 

 had employed the various verification methods. Sev- 

 eral of these used the combination of tag-recapture, 

 length-frequency and OTC marking for verification 

 or validation (or both) of the calcified structure age 

 estimates. Growth estimates from a laboratory and 

 field study of the Atlantic sharpnose shark [Rhizo- 

 prionodon terraenovae) (Branstetter 1987a) corre- 

 sponded well to estimates generated with length fre- 

 quencies and vertebral rings (Parsons, 1985). Casey 

 et al. ( 1985 ) used length-frequency, vertebral and tag- 

 recapture analyses to verify age estimates for the 

 sandbar shark, C. phimbeiis, and concluded that 

 there was close agreement with all three methods. 

 Pratt and Casey (1983) also used these three meth- 

 ods to age the shortfin mako, Isurus oxyrinchus, and 

 concluded that not only was there agreement between 

 the methods but that tagging did not affect growth 

 in this species. Smith (1984) validated the periodic- 

 ity of vertebral band deposition in the leopard shark, 

 Triakis semifasciata using OTC. Kusher et al. ( 1992 ) 

 were able to confirm these results as well as use 

 length-frequency data and additional tag-recapture 

 data to produce independent age estimates for this 

 species. The tag-recapture curve gave slower k val- 

 ues than the vertebral, and although the k values 

 were not significantly different, the authors sug- 

 gested that tagging may have had an effect on growth 

 in this species (Kusher et al. 1992). These results 

 accentuate the requirement of good tag and recap- 

 ture data as a backup for vertebral studies, particu- 

 larly if combined with OTC injections for validation. 

 In the case of the tiger shark in this study, tag-re- 

 capture and length-frequency data have provided 

 independent estimates of growth for verification. In 

 addition, the results present evidence against the 

 suggestion that tagging, with or without OTC injec- 

 tion, decreases the growth rate of sharks. It can be 

 argued that the tiger shark cannot be used to gener- 

 alize about sharks because they grow rapidly in re- 

 lation to many other species. A birth size of 61 cm FL 

 with a corresponding weight of 1.8 kgs. is small in 



relation to many large coastal species, such as the 

 dusky shark ( size and weight at birth: 81 cm FL and 

 7 kgs., respectively Castro, 1983; Kohler et al., 1995) 

 and the silky shark (size and weight at birth: 64 cm 

 FL and 9 kgs., respectively). If these relatively small 

 tiger shark young can withstand the rigors of tag- 

 ging and continue to grow at a similar rate as 

 untagged individuals, then it is certainly reasonable 

 to believe that a larger shark can as well. Regard- 

 less, all species need to be evaluated individually for 

 their reactions to tagging and OTC injection. 



Acknowledgments 



We are thankful to the thousands of fishermen who 

 voluntarily tag and return tags to us and thus make 

 this continuing program possible. We thank Chris 

 Jensen who helped in tagging and injecting tiger 

 sharks with tetracycline as well as providing accu- 

 rate measurements on both tagged and recaptured 

 specimens. Fisherman Eric Sander provided dozens 

 of vertebrae from precisely measured recaptured 

 young tiger sharks as well as from nontagged speci- 

 mens. We also thank Steve Branstetter for discus- 

 sions on the phone and for reviewing the manuscript. 

 Greg Cailliet and Sabine Wintner also provided in- 

 valuable comments on the manuscript. We appreci- 

 ate the encouragement and assistance of our col- 

 leagues in the Apex Predators Program. 



Literature cited 



Anonymous. 



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