135 



Abstract. -Age and growth of the 

 blacktip shark, Carcharkinus limbatus, 

 from the east coast of South Africa were 

 investigated by counting growth rings 

 in vertebral centra. The vertebrae of 41 

 females (41-181 cm precaudal length 

 [PCL]> and 51 males (42-182 cm PCD 

 were examined. Three methods suc- 

 cessfully enhanced the visibility of 

 growth rings: crystal violet staining of 

 the centrum face, microscopic examina- 

 tion of the whole vertebra, with trans- 

 mitted light and dark field, and "bow 

 tie" sectioning of the vertebra. The re- 

 sults of the three methods were com- 

 pared by using the average percentage 

 error index and statistical means. Age 

 and growth estimates were obtained 

 from microscopic examination of the 

 whole vertebra, the method which pro- 

 vided the most accurate ring counts and 

 gave the second highest reproducibility. 



The data for males and females were 

 combined and the von Bertalanffy pa- 

 rameters obtained were L^= 193.6 cm 

 PCL, K = 0.21yr 1 and t = -1.2 yr. Age 

 at maturity was 7 years (156 cm PCL) 

 for females and 6 years ( 150 cm PCL) 

 for males. The oldest aged female was 

 11 years (179 cm PCL), the oldest aged 

 male was 10 years (179 cm PCL) old. 

 Mean calculated growth rates were 24 

 cm/yr for the first three years, 11-13 

 cm/yr through adolescence, and 5-6 cm/ 

 yr after maturity. 



Back-calculated lengths were lower 

 than observed lengths and Lee's phe- 

 nomenon was apparent. In 83% of the 

 vertebrae the band immediately after 

 the change in angle was translucent. 

 Opaque band deposition is assumed to 

 occur in summer. 



Age and growth determination 

 of the blacktip shark, 

 Carcharhinus limbatus, 

 from the east coast of South Africa 



Sabine R Wintrier 

 Geremy Cliff 



Natal Sharks Board, Private Bag 2 

 Umhlanga Rocks 4320, South Africa 



Manuscript accepted 16 October 1995. 

 Fishery Bulletin 94:135-144 ( 1996). 



The Natal Sharks Board (NSB) op- 

 erates a shark fishery on the east 

 coast of South Africa that is aimed 

 at protecting beach users against 

 shark attack (Cliff et al., 1988a). 

 The sharks are caught in large-mesh 

 gill nets, which fish throughout the 

 year off the more popular recreational 

 beaches of KwaZulu-Natal. Concern 

 has arisen over the possible impact 

 of over 30 years of gillnetting on shark 

 populations off this coast (Dudley and 

 Cliff, 1993a). One of the 14 species 

 contributing to the annual catch of 

 about 1,440 sharks is the blacktip 

 shark, Carcharhinus limbatus. Be- 

 tween 1978 and 1994 an annual av- 

 erage of 121 C. limbatus were caught 

 in the nets. Information about the dis- 

 tribution, fecundity, size at maturity, 

 diet, and movements of C. limbatus 

 is given by Bass et al. (1973) and 

 Dudley and Cliff (1993b). 



Research on ageing is an integral 

 part of life history studies of ex- 

 ploited species. This study estimates 

 age and growth of C. limbatus from 

 vertebral ring counts. Comparable 

 information exists for this species 

 from the Gulf of Mexico (Branstetter 

 and McEachran, 1986; Branstetter, 

 1987a; Killam and Parsons, 1989). 



Materials and methods 



Sampling 



Sharks were sampled in the NSB 

 nets from 1985 to 1991. Each net 



was 214 m long, 6 m deep, had a 

 50-cm stretched mesh, and was set 

 in water 10-14 m deep, parallel to 

 and 300-400 m from the shore. For 

 details of the netting operation see 

 Cliff etal. (1988a). 



Precaudal length (PCL) was mea- 

 sured in a straight line from the 

 snout tip to the precaudal notch and 

 was used throughout this study. For 

 comparison with literature which 

 reported total length (TL), as de- 

 fined by Branstetter (1987b), the 

 following equation was generated 

 by Dudley and Cliff ( 1993b); 



TL = 1.334 x PCL + 4.27 



[rc=94, r=0.999; 

 range 40.5-190.0 cm] 



Maturity was assessed on the 

 basis of the criteria of Bass et al. 

 (1973). Males were considered ma- 

 ture only if the claspers were fully 

 calcified. Sperm is produced before 

 claspers are fully calcified and was 

 therefore not regarded as a criterion 

 of maturity. Females were consid- 

 ered mature by the presence of a 

 ruptured hymen and large eggs 

 (>15 mm diameter) in the ovary. In 

 addition, a uterus width of more 

 than 5 cm indicated maturity 

 (Dudley and Cliff, 1993b). 



Vertebral samples were taken 

 anterior to the origin of the first 

 dorsal fin from 41 females (41-181 

 cm) and 51 males (42-182 cm). The 

 vertebrae were stored in various 

 ways: dry (71%); in 70% isopropyl 



