348 
Fishery Bulletin 108(3) 
Figure 1 
Digital image (2x magnification) of vertebral section from a 36-year old male hammerhead 
shark ( Sphyrna mokarran) (SM-114), captured 14 January 2004. White dots denote single 
winter growth bands used to assign age. White line near base of centrum denotes birth band. 
and 1967, respectively (Fig. 1). These estimates fall 
within the range of dates useful for bomb radiocarbon 
analysis and indicate that the specimens were both 
born during the initial rise in 14 C. Bomb radiocar- 
bon analysis yielded results for seven samples from 
SM-112 and three from SM-114 (Table 1). Values of 
<5 13 C were relatively stable over the range of samples 
(mean=-11.0, standard deviation [SD] = 0.1) and were 
similar to those from other elasmobranch species, 
verifying a dietary (metabolic) carbon source (Fry, 
1988; Campana, 1997; Campana et al., 2006). The 
mean standard deviation of the individual radiocarbon 
assays was about 5 %o. 
Values of z\ 14 C in S. mokarran ranged from 18.6 to 
148.3 units, reaching a maximum in the early 1970s 
(Fig. 2). The birth dates of the two sharks were not 
quite old enough for us to document the initial year 
of radiocarbon increase, which likely occurred before 
1961. Given the available data, the trend in timing and 
magnitude of the 4 14 C chronology for all of the S. mo- 
karran samples most closely resembled that of Florida 
coral. Timing of the period of increase and peak in 4 14 C 
was also similar between S. mokarran and porbeagle 
chronologies, but there were large differences in abso- 
lute values. 
When trends in Z\ 14 C for the two specimens were 
examined individually, a difference in trajectories 
was apparent between SM-112 and SM-114. Values 
from both specimens fell mostly along the curve of 
the coral chronology, with one exception. The sample 
