Andrews et al.: Bomb radiocarbon and tag-recapture dating of Carcharhinus plumbeus 
459 
Figure 2 
Plot of sandbar shark ( Carcharhinus plumbeus) A 14 C measured from vertebrae in relation 
to the estimated year of formation (determined from growth band counts), showing that 
an adjustment of formation dates for sandbar shark specimen SB 749 (by an additional 10 
years) was necessary to match the porbeagle ( Lamna nasus) A 14 C record (filled diamonds). 
Minimum adjusted age was 26 years. The assumption was made that the missing years 
were those in the late-adult years (as reflected in the outer part of corpus calcareum 
where band resolution can be lost) and that early growth was well quantified. 10 years 
was added to the time between the known-age edge material and the next sample inward 
in the corpus calcareum ( cf. 1974 with 1963). For this sample series, the youngest sample 
(juvenile portion of corpus calcareum) was classified as contaminated with older (postbomb) 
adult material and was eliminated from consideration because of its unexpectedly high 
A 14 C value (denoted as an X in the projected growth scenario). 
of 73—140 cm FL were recaptured after a minimum of 
10 years at liberty (TAL 10.0-27.7 years). Ages for these 
sharks ranged from 13.1 to 36.0 years (Table 3). The tag 
of the shark at liberty 27.7 years was compromised over 
time: the last of 3 digits on the tab was worn off by the 
time of recapture. This shark was one of ten sandbar 
sharks measured and tagged on the same day within 
this number series. These sharks ranged in size from 99 
to 122 cm FL at recapture and longevity was estimated 
at 33 to 36 years for these sharks for this longest period 
before recapture. 
One OTC-tagged recaptured shark was examined 
that measured 68 cm at tagging and 150.4 cm FL 
at recapture. Time at liberty was 11.8 years and the 
estimated age at tagging was 1.6 years. Twelve band 
pairs were visible after the OTC mark as determined 
by the criteria of Casey et al. (1985) and the total esti- 
mated age was 13.6 years. This estimate was one year 
more than the growth curve estimate (12.6 years), but 
was within the margin of uncertainty of the growth 
function. 
Re-examination of vertebrae 
Because the bomb radiocarbon analyses revealed dis- 
crepancies in age, four of the original histological sec- 
tions were re-examined to determine whether banding 
existed in the sections that would correspond with the 
bomb radiocarbon ages. Many additional band pairs 
were visible in the vertebrae of these specimens and 
support the ages indicated by the bomb radiocarbon 
analyses. These band pairs were not considered to rep- 
resent annual growth in the early study because they 
did not fit the criteria defined in the study and were 
not counted. If an approach were used to count all band 
pairs, this would also indicate that the age-validated 
specimen SB 43 was more than 10 years old (maximum 
addition of three years in relation to coral zl 14 C records). 
In addition, the recently collected OTC-marked specimen 
would necessarily have an age greater than the known 
TAL and lead to the conclusion that early growth was 
not underestimated. These findings indicate that the 
band pair counts with the Casey et al. (1985) criteria 
