Wintner and Cliff. Age and growth determination of Carcharhinus limbatus 



143 



similar to those obtained with the UT method and 

 higher than those from the Gulf of Mexico. With the 

 BT method, mature sharks grew at a rate of 3 cm/yr, 

 which is slower than the 5-6 cm/yr of the UT method, 

 but similar to the values obtained by Killam and 

 Parsons (1989). 



It is therefore possible that the UT method, by 

 overestimating the growth of mature animals, may 

 underestimate the age of these sharks. Nevertheless, 

 given the large differences in size at birth and matu- 

 rity and in maximum size between sharks of the two 

 populations (Table 3), there is no apparent reason to 

 question the large differences in growth rates be- 

 tween immature sharks of the two populations. 



Dudley and Cliff (1993b) found that 66% of 

 C. limbatus caught in NSB nets were mature. If age 

 at maturity of females is taken at seven years, maxi- 

 mum age at 11 years, the gestation period as 14 

 months, and the median litter size as six (Dudley 

 and Cliff, 1993b), the maximum fecundity of a fe- 

 male is about 24 pups. Most carcharhinids have a 

 two-year reproductive cycle (Branstetter, 1981), but 

 there is evidence for a three-year reproductive cycle 

 in C. limbatus from South Africa (Dudley and Cliff, 

 1993b). Catch rates for this species since 1978, the 

 earliest period for which accurate catch data are 

 available, have shown no trend (Dudley and Cliff, 

 1993b) and can be interpreted as reflecting a rela- 

 tively constant annual harvesting of immigrants 

 (Wallet, 1973; Cliff et al., 1988b). Despite its low fe- 

 cundity, catches are sustained by the wide distribution 

 of C. limbatus in the western Indian Ocean, in which 

 the small netted region falls largely outside the nurs- 

 ery grounds of this species (Dudley and Cliff, 1993a I. 



Acknowledgments 



The assistance of the field staff of the Natal Sharks 

 Board, who provided specimens and associated in- 

 formation, is greatly appreciated. The laboratory staff 

 was responsible for dissecting many sharks and for 

 collecting and storing the vertebrae. We would like 

 to thank A. T Forbes for his comments and S. F. J. 

 Dudley for his assistance. 



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