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Fishery Bulletin 101(2) 



to that found in the present study for the finetooth shark. 

 However, future validation studies through chemical mark- 

 ing, tag-recapture, or bomb dating are needed to determine 

 that growth bands are deposited annually for the finetooth 

 shark as well as numerous other species. 



Very few studies have applied the method of Fabens 

 ( 1965 ) for estimating growth in sharks, but some have sug- 

 gested that using an estimate of size at birth (Lq) rather 

 than tg is a more robust technique (Goosen and Smale, 

 1997). In the present study, the estimates of K obtained 

 with the Fabens ( 1965) method were slightly higher than 

 those estimated with the original von Bertalanffy (1938) 

 equation, probably because the former method forces the 

 model through the y-intercept, making the initial part of 

 the curve steeper (Fig. .3). Beyond age 1, both models were 

 very similar for both sexes and in some cases overlapped 

 in size at age. In addition, the estimates of productivity, 

 generation time, and elasticities, where results from ei- 

 ther model were used, were very close. The similarities 

 in growth models with both techniques (Fabens and von 

 Bertalanffy) are likely a reflection of adequate samples 

 throughout all ages. The application of the Fabens ( 1965 ) 

 method may be appropiate when there is an inadequate 

 sample of very small individuals. 



Differences in reproduction may exist between finetooth 

 sharks from the Gulf of Mexico and northwestern Atlantic 

 Ocean. Although not subjected to a quantitative analysis, 

 Castro ( 1993) reported size at maturity to be about 1300 mm 

 STL ( 1271 mm TL) for males and 1350 mm STL ( 1320 mm 

 TL) for females off South Carolina. This is approximately 

 80-90 mm TL greater than the median size at maturity es- 

 timated for finetooth sharks from the Gulf of Mexico. There 

 is growing evidence that differences in life-history traits 

 between geographically separated populations of sharks are 

 not unusual. To cite a few examples, Parsons ( 1993a, 1993b ) 

 and Carlson and Parsons ( 1997) found a clinal variation in 

 reproduction and age and growth among populations of bon- 

 nethead sharks from the eastern Gulf of Mexico; Wintner 

 and Cliff (1995) found that size at maturity differed greatly 

 between blacktip sharks from South Africa and the Gulf 

 of Mexico; and Mollet et al. (2000) found that the median 

 length at maturity for female mako sharks ilsu/'us oxyrin- 

 chus) is greater in the western north Atlantic Ocean than 

 in the southern hemisphere. Whether these deviations in 

 life-history parameters are the result of phenotypic plastic- 

 ity or genotype is yet to be determined. 



Despite no known directed or indirect fishing mortality 

 on the population of finetooth sharks from the northeastern 

 Gulf of Mexico, younger age classes (ages and 1) were not 

 very important. Our sampling design incorporated a mul- 

 tiple-mesh gill net that was thought to capture all sizes of 

 juvenile sharks (Carlson and Brusher, 1999). However, be- 

 cause selectivity functions have not been calculated for this 

 species, we cannot ascertain whether these age groups are 

 indeed naturally low in abundance in the areas sampled or 

 whether this finding is an artifact due to sampling bias. 



In addition to age and growth characteristics, the fine- 

 tooth shark exhibits other life-history traits and population 

 parameters that fall betww'n those of the blacktip shark 

 and those of other small coastal species (Table 3). Indeed, 



this species can be placed between the blacktip shark and 

 the Atlantic sharpnose shark and bonnethead along the 

 continuum of productivity estimates (r^, with Z=2 M) of 

 Smith et al. ( 1998), and also between the blacktip shark and 

 the Atlantic sharpnose shark, bonnethead, and blacknose 

 shark in the "fast-slow" continuum of life-history traits and 

 population parameters identified by Cortes (see his Fig. 2, 

 2002). Thus, the finetooth shark appears to be the "slow- 

 est" of the small coastal sharks studied so far, and to have 

 moderate rebound potential and intermediate generation 

 time. In addition, the probabilistic elasticity analysis indi- 

 cated that population growth rates of finetooth sharks are 

 much more sensitive to survival of the juvenile and adult 

 stages than to survival of age-0 individuals or fecundity, as 

 recently found for a suite of shark species (Cortes, 2002). 

 This finding suggests that management actions should fo- 

 cus on protection of juveniles and adults rather than age-0 

 individuals, a recommendation that generally applies to 

 sharks located towards the "fast" end of the life-history 

 continuum. Minimum size limits could thus be effective 

 measures to enhance juvenile survival and time-area clo- 

 sures could protect reproductive females, adult survival, 

 and reproductive potential, should stocks of this species 

 become overfished and management actions be required. 

 Moreover, this study suggests that, when feasible, sharks 

 should be managed on a species-specific basis, rather than 

 by groupings of multiple species that may ignore marked 

 differences in life-history traits. 



Acknowledgments 



We thank the staff of the National Marine Fisheries 

 Service, Panama City, FL, for their help throughout this 

 study. Special thanks go to Karen Hanson for cleaning and 

 sectioning all the vertebrae. Henry Mollet provided guid- 

 ance with determining size at maturity. We also thank Lee 

 Trent, and the many interns who provided assistance with 

 collection of sharks. All animals were collected under the 

 Florida Department of Environmental Protection Special 

 Permit no. 96S-075. 



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