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Fishery Bulletin 97(1), 1999 



1 GR, increasing to 51 kg (4-5 GRs), 78 kg (7-8 GRs) 

 and 94 kg (12-13 GRs). Shark BT433 grew 69 cm 

 and 104 kg in 2.6 years (Fig. IB) which represents a 

 mean annual growth of 27 cm and 40 kg. 



Discussion 



Annual GR periodicity has been partly verified for 

 several species (Cailliet, 1990). For some species of 

 the family Lamnidae, biannual GR periodicity has 

 been reported. Parker and Stott ( 1965) used the mean 

 length of 17 Cetorhinus maximus sampled in winter 

 and 15 sampled in summer and treating them as age 

 classes, derived a tentative growth curve. They stated 

 that their growth curve derived from ring counts of 

 live vertebrae was similar to the first one when a depo- 

 sition of two GRs per year was assumed. They were, 

 however, careful to note that there was "nothing to in- 

 dicate beyond doubt that the addition of two rings is 

 the direct result of the passage, of an annual seasonal 

 cycle" and said that several findings did not "harmonise 

 with the idea of annual increase of two rings." 



Pratt and Casey ( 1983) determined age and growth 

 of Isurus oxyrinchus from the Atlantic by length- 



month analysis, length-frequency analysis, tag-re- 

 capture information, and vertebral ring counts. The 

 results of the first analysis were used to interpret 

 the accuracy of the other methods. Their growth 

 curve for /. oxyrinchus, based on back-calculated 

 sizes, agreed closely with those obtained by the other 

 methods if biannual ring deposition was assumed. 

 The vertebrae from four noninjected recaptured /. 

 oxyrinchus, however, gave inconclusive results be- 

 cause two supported annual and the other two bian- 

 nual GR deposition. Pratt and Casey stated that "ver- 

 tebral rings may thus yield an approximation of age, 

 accurate in the smaller sizes where estimates have 

 been correlated with other methodologies. Adults 

 may not lay down yearly, and it is possible that we 

 have underestimated their age, but we have no data 

 to support this possibility." 



Cailliet et al. ( 1983a) assumed annual GR deposi- 

 tion in /. oxyrinchus from California waters. Their 

 growth rate estimates, based on tag-recapture analy- 

 sis, were therefore half of those of Pratt and Casey 

 (1983) and had a much smaller variation in the esti- 

 mate. Cailliet et al. ( 1983a) stated that although "this 

 discrepancy could be related to differences in habi- 

 tat or environmental conditions or differences in 



