Wintner and Cliff: Age and growtfi determination of Carcharodon carcharias 



163 



■S 



s 



o 



100 

 90 

 80 - 

 70 



I 1 Weight 



■^■Length 



Weight 



Length 



5 6 7 8 



Number of growth rings 



10 



12 



13 



Figure 8 



Observed ( bar ) and predicted (line ) growth in mass and length per growth ring for the white shark, 

 C. carcharias. Growth ring estimates were obtained by using method SC-A. 



sample size or ageing methodology" it was interest- 

 ing to note "that the growth rate reported by Pratt 

 and Casey (1983) based on their back-calculation 

 from counts of bands on centra, would be similar to 

 ours if each pair of bands from their fish were inter- 

 preted as an annual event." 



Cailliet et al. ( 1985) assumed annual GR periodic- 

 ity in their age and growth study of C. carcharias. 

 As with the studies mentioned above, MIR analysis 

 could not be included to validate the temporal peri- 

 odicity of the GRs. The only lamnoid study to have 

 done so, apart from this one, was that of Branstetter 

 and Musick (1994) on Carcharias taurus, which sug- 

 gested a semiannual periodicity of band and ring for- 

 mation. However, samples from three winter months 

 were lacking. They also used a "odd-even ring count 

 analysis" to verify this suggestion. 



The results of the MIR analysis (Fig. 5) were in- 

 conclusive and did not confirm the results fi-om shark 

 BT433. Considerable time was spent on this analy- 

 sis and great care was taken to discern the last de- 

 posited band in order not to overlook a recently 

 formed band. Several vertebrae were remeasured, 

 resulting only in removing the peaks of the curve 

 and not in a reduction of the minimum MIR. Exami- 

 nation of the relative frequency of vertebrae with 



large MIR to those with low MIR plotted against 

 month (Batista and Silva, 1995) did not shed light 

 on this issue. Annual or biannual GR periodicity for 

 C. carcharias could not be confirmed in this study by 

 two centrum edge analyses. 



There seems to be some unexplained variation in 

 GR deposition among lamnoids, which is further com- 

 pounded by our study Pratt and Casey ( 1983) stated 

 that in /. oxyrinchus instead of the traditional an- 

 nual ring deposition "a more likely cause for ring for- 

 mation would be times of stress or deprivation such 

 as migration and mating." Similarly, Branstetter and 

 Musick (1994) suggested that in C. taurus the for- 

 mation of semiannual bands may reflect their north- 

 south seasonal migration pattern, which is prompted 

 in part by changing light and temperature patterns. 

 There is currently not enough evidence to prove a 

 similar migration pattern for C. carcharias in South 

 African waters (Cliff et al., 1996a, 1996b). 



Traditionally, ages of sharks have been related to 

 length (Cailliet et al., 1983b; Cailliet et al., 1986). 

 Natanson and Cailliet (1990) found that band depo- 

 sition in Squatina californica was not annual but 

 related to somatic growth. We therefore decided to 

 fit a Gompertz growth curve because this curve usu- 

 ally describes the relationship between mass and age 



