632 



Fishery Bulletin 101(3) 



Figure 3 



Vertebral sections from two OTC-injected blue sharks [Prionace glauca). Annuli and 

 birth marks are indicated. 



Discussion 



Several methods have been employed to vali- 

 date or verify (or both) age estimates derived 

 from vertebral banding patterns (Cailliet, 1990). 

 Although corroborative verification often comes 

 from the interpretation of length-frequency data, 

 laboratory and field growth studies, and centrum 

 edge analyses, direct age validation for sharks is 

 limited to the interpretation of vertebral banding 

 patterns in OTC-injected fish. 



In his review of elasmobranch age and growth 

 studies, Cailliet (1990) found validated growth 

 curves for only six species, which included three 

 carcharhinids: the lemon (Negaprion brevirostris); 

 the sandbar (Carcharhinus plutnbeus); and the 

 Atlantic sharpnose [Rhizoprionodon terraenovae) 

 sharks. Although more than ten years have trans- 

 pired since this review, validated growth curves for 

 sharks are still lacking. In lamnids, direct valida- 

 tion of annual band deposition with the use of OTC 

 has been reported in a single species, the porbeagle 

 shark, Larnna nasus (Natanson et al., 2002). Al- 

 though age estimates from vertebral banding pat- 

 terns have been reported for several carcharhinids, 

 including the oceanic whitetip shark, Carcharhin us 

 longimanus (Seki et al., 1998; Lessa et al., 1999), the 

 dusky shark, C. obscurus (Natanson et al., 1995; Natanson 

 and Kohler, 1996; Simpfendorfer, 2000), the blacktip shark, 

 C. limbatus (Wintner and Cliff, 1995 ), and the bronze whaler, 

 C. brachyurus (Walter and Ebcrt, 1991 ), ago interpretations 

 were not validated and vertebral bands were assumed to be 

 annual. More recently, Simpfendorfer ot al. (2002) validated 

 the annual formation of vertebral banding patterns in C. 

 obscurus from Western Australian waters. 



In the current study, we have validated annual band pair 

 deposition in Prionace glauca up to 4* years in age using 



Age (yr) of reader 1 



Figure 4 



Age bias graph for pair-wise comparison of 98 blue shark i.Prio- 

 nace glauca) vertebral counts from two independent readers. Each 

 error bar represents the dSVr confidence interval for the mean age 

 assigned by reader 2 to all fish assigned a given age by reader 1. 

 The one-to-one equivalence line is also presented. 



vertebrae from two OTC-injected fish. These data indicate 

 that annulus formation occurs in the spring. This seasonal 

 formation is further supported by the marginal increment 

 analysis of Skomal ( 1990 ), which shows that one band pair is 

 formed annually. However, the low sample size and the lack 

 of OTC-injected recaptured fish over the entire size range of 

 the species do not allow for full age and growth validation. 

 Clearly, the study requires OTC-injected recaptured blue 

 sharks over a broader size range and greater time at lib- 

 erty — a requirement that is not atypical of age and growth 



