Andrews et al.: Bomb radiocarbon and tag-recapture dating of Carcharhinus plumbeus 
457 
Table 2 
Summary of results from radiocarbon analyses. Estimated shark age from growth band counts with calculated birth year, year 
of growth-band formation, and ages for each sandbar shark ( Carcharhinus plumbeus) vertebra. Resultant A 14 C values and the 
adjusted year of growth-band (GB) formation for each sample are given along with bomb radiocarbon age of the shark, where 
applicable. SD=standard deviation 
Age determined from growth bands 
Age determined 
from radiocarbon data 
Sample Shark age 
number (yr) 
Year of GB 
formation 
Age 
sampled 
A 14 C (SD) 
(%o) 
Adjusted 
year 
Shark age 
(yr) 
SB 43 
1955 
N.C. 2 
1957 
2 
-67.6(4.2) 
N.C. 2 
1963 
8 
-21.2 (3.6) 
N.C. 2 
10.3 
1965 
10.3 
SB 47970 
1971 
1960 
1972 
1 
-79.8 (4.1) 
1962 
1977 
6 
125.3 (5.9) 
1967 
14.2 
1985 
25 (23-27) 
SB 745 
1960 
1955 
1961 
1 
-64.3 (4.0) 
1956 
1967 
7 
-78.6(3.9) 
1962 
16.4 
1976 
>20 
SB 118 
1950 
N.C. 2 
1951 
1 
-53.3(4.2) 
N.C. 2 
1965 
15 
N.M. 3 
15.6 
1966 
N.C. 2 
SB 749 
1965 
1954 
1966 
1 
-7.8 (4.4) 
1955 
1967 
2 
-110.9 (3.9) 
1956 
1970 
5 
-70.6(3.9) 
1959 
1974 
9 
-61.7(4.0) 
1963 
1980 
15 
16.6(4.6) 
1980 
16.1 
1981 
>26 
1 No change: Values in alignment with calibration curves. 
2 No change: Not enough information to assess an adjustment (with prebomb reference) 
3 Not measured: Sample was lost during preparations for accelerator mass spectrometry. 
with two diamond blades separated by a 0.6-mm spacer. 
Photographs of both sections were taken — the thicker 
sections under UV light and the thinner histological 
sections under reflected lighting. Resulting photographs 
were superimposed to determine the location of the OTC 
mark on the histological section and counts and mea- 
surements were determined from the combined images. 
Results 
Bomb radiocarbon dating 
Values of A 14 C measured in sandbar shark vertebrae, 
provided in parts per million (%c) ±1 standard devia- 
tion [ SD] ), ranged from prebomb to peak and postbomb 
levels (Table 2). Prebomb levels were similar to those 
in the porbeagle record, with values as low as -110.9 %c 
(SD = 3.9). The peak A 14 C value exceeded expectations 
and was similar in magnitude to hermatypic coral 
Z\ 14 C records (125. 3%c, SD = 5.9). Despite the strong 
indication of bomb-produced radiocarbon in several 
vertebrae, the growth-band derived years of formation 
for many of the samples were not in agreement with 
the bomb radiocarbon dating A 14 C references (Fig. 1). 
One sample was lost from specimen SB 118; therefore, 
the vertebra was useful only as a prebomb A 14 C refer- 
ence value. The age of the youngest specimen (SB 43), 
estimated at 10.3 years, was supported by the A 14 C 
results; yet the estimated ages of the other three adult 
