BRANSTETTER ET AL.: AGE AND GROWTH OF TIGER SHARK 



cycle is at least 2 years. Considering the litter size 

 (40-70 pups) (Kauffman 1950; Bass et al. 1975; Bran- 

 stetter 1981), natural mortality must be high for 

 young age classes. Pups are born in coastal waters 

 at a relatively large size (>70 cm) which reduces 

 some predation, but the elongate, flexible body pro- 

 duces an inefficient anguilliform swimming motion. 

 Additionally, early in life, the caudal fin is extremely 

 flexible and has a low thrust angle (Thompson and 

 Simanek 1977). The combination of these charac- 

 teristics precludes rapid swimming speeds, thus 

 making the pups vulnerable to predation by the 

 abundant coastal sharks including their own species. 

 Not only does rapid linear growth make them larger 

 than most potential predators, it may help decrease 

 predation by increasing swimming efficiency and 

 speed through increased body rigidity (producing a 

 more carangiform motion) and increased caudal fin 

 thrust angle. 



Linear growth continues at >20 cm/year until the 

 tiger sharks are near maturity. Such rapid growth 

 is similar to that noted for several lamnoids (Parker 

 and Stott 1965; Gruber and Compagno 1981; Pratt 

 and Casey 1983; Cailliet et al. 1985), but contrasts 

 sharply to the slow growth rates estimated for 

 several carcharhinids and sphyrnids (Thorson and 

 Lacy 1982; Gruber and Stout 1983; Schwartz 

 1983a). Even the more rapidly growing carchar- 

 hinids do not have such large relative increases in 

 length (Parsons 1985; Branstetter and McEachran 

 1986). 



The mean lengths at age between the Gulf of Mex- 

 ico and Atlantic tiger sharks were significantly 

 different, and probably represent ecophenotypic dif- 

 ferences between the two regions. However, the two 

 regional groups are not isolated. Our one tag- 

 recapture was tagged off Mobile Bay, AL and recap- 

 tured in the Florida Straits off Havana, Cuba, and 

 there are similar tag returns of tiger sharks that 

 moved between the Gulf of Mexico and the Atlan- 

 tic (J. Casey pers. commun."*). However, long migra- 

 tions between the two regions may be restricted to 

 larger individuals with juveniles remaining in their 

 respective regions. 



If juvenile tiger sharks do remain in their respec- 

 tive regions early in life, growth rate differences 

 between the two regions may be caused by dif- 

 ferences in early life histories. In the Gulf of Mex- 

 ico, the pups apparently only migrate short distances 

 inshore-offshore seasonally. In the Atlantic, the pups 



^J. Casey, Northeast Fisheries Center Narragansett Laboratory, 

 National Marine Fisheries Service, NOAA, South Ferry Road, 

 Narragansett, RI 02882, pers. commun. June 1986. 



are born south of Cape Hatteras, probably in the 

 Florida region (Dodrill 1977). These neonates may 

 not migrate north during their first year, as small 

 individuals, <150 cm, are rare in the Virginia region 

 (Fig. 5). During this time, the growth rates for both 

 groups are similar. The extensive northern 

 migration for l-i- year old Atlantic juveniles, 

 150-200 cm, may be energetically costly, hinder- 

 ing growth. Therefore, the Gulf young that do not 

 migrate great distances are able to attain greater 

 lengths during this time period. The increased 

 swimming efficiency attained with lengths >250 cm 

 could possibly explain why growth rates become 

 similar. 



For juveniles of both regions, the energy require- 

 ments for the inefficient swimming motion and rapid 

 linear growth apparently restrict any great increase 

 in weight (Fig. 6). Only after the tiger sharks reach 

 lengths >200 cm (3 -i- years of age) does weight in- 

 crease substantially, and correspondingly linear 

 growth begins declining. After reaching maturity 

 (310-320 cm) linear growth is <10 cm/year while 

 weight growth is substantial, corresponding to the 

 change in centrum radius/length relationship (Fig. 

 3). 



The von Bertalanffy parameter estimates for the 

 two collections closely bracket known life history 

 characteristics. With sexes combined, the L^ for 

 the Gulf of Mexico collection and for both samples 

 combined (388 cm) is smaller than many reported 

 large individuals, but is a reasonable compromise 

 between the maximum reported lengths for males 

 and females: 419 cm individual (McCormick et al. 

 1964); 370 cm male, 410 cm female (Bass et al. 1975); 

 410 cm female (Branstetter 1981); and a 381 cm 

 male and female from this study. However, the tiger 

 shark is thought to attain lengths in excess of 450 

 cm (Bigelow and Schroeder 1948; Castro 1983), 

 more in agreement with the L^ for the Atlantic 

 sample (440 cm). The t^ value for the Gulf sample 

 (-1.13 years) is accurate, but the 13-16 mo gesta- 

 tion period is overestimated for the Atlantic sam- 

 ple (-2.35 years). The ^o value for many shark 

 species overestimates the gestation period (Casey 

 et al. 1985; Branstetter 1986). The iiT values for each 

 analysis reflect the rapid growth rate of this species 

 and are similar to some of the more rapidly grow- 

 ing Carcharhinus species such as C. limbatus, C. 

 brevipinna (Branstetter 1987c), C. falciformis 

 (Branstetter 1987b), and C. acronotus (Schwartz 

 1983b). 



At the estimated growth rate for the largest in- 

 dividuals (5-10 cm/year), exceptionally large speci- 

 mens, 400-450 cm, would be 20-25 years of age. The 



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