Campana and Jones: Radiocarbon applied to age validation of Pogonias cromis 
89 
Year class 
Figure 2 
A 14 C in the otolith cores of adult black drum in relation to the year class 
estimated from counts of presumed annuli. The A 14 C values have been fitted 
with a LOWESS curve. 
Year class 
Figure 3 
A 14 C values in the otolith cores of adult black drum in relation to published 
A 14 C chronologies for the atmosphere, corals from Bermuda and Florida, 
and haddock otoliths from eastern Canada. Whereas peak A 14 C values dif- 
fered among the time series, all shared a similar period of increasing values, 
with the source of the 14 C (the atmosphere) predating the coral and haddock 
time series by 2-4 years. The black drum chronology lies intermediate in 
phase and value to the atmospheric and marine carbonate time series, re- 
flecting an estuarine origin. The two coral chronologies are drawn from 
Druffel (1989), and the chronologies for the atmosphere and haddock are 
from Nydal (1993) and Campana (1997), respectively. 
could only increase the A U C value, not 
decrease it. Thus the A 14 C value sets a 
minimum age for the sample, and the 
years 1958-65 become the most sen- 
sitive years for A 14 C-based ageing. It 
is on this basis that workers in other 
disciplines have used bomb radiocar- 
bon assays to infer age and the fre- 
quency of growth-ring formation in 
both bivalves (Turekian et al., 1982; 
Peck and Brey, 1996) and mammals 
(Bada et al., 1990). 
The coherence between the otolith- 
based 14 C time series reconstruction 
reported here and that reported else- 
where in the North Atlantic for bi- 
valves (Weidman and Jones, 1993), 
corals (Druffel, 1989), and haddock 
otoliths (Campana, 1997) indicates 
that black drum age assignments 
were, on average, reasonably accurate 
(Fig. 3). The similar prebomb A 14 C his- 
tories for these taxa reflect a common 
baseline value, whereas differences in 
post-1970 histories reflect geographic 
variability in water mixing times 
(Weidman and Jones, 1993). However, 
the differences in phase, magnitude, 
and postbomb decline among the vari- 
ous A 14 C chronologies are both signifi- 
cant and meaningful and suggest that 
more accurate age interpretations may 
be possible. To improve ageing accu- 
racy, however, three additional as- 
sumptions must be met: 1) the ex- 
tracted otolith core must not be con- 
taminated with material of more re- 
cent origin; 2) annulus interpretations 
and any associated errors must be 
made consistently across all ages ex- 
amined; 3) the 14 C “reference” chro- 
nologies must be synchronous with 
that of the fish species under study. 
The first assumption has only been 
tested by Campana ( 1997 ) for haddock 
but was found to hold in part; intact 
age-1 otoliths and the extracted core 
of older fish from the same year class 
were characterized by similar A 14 C 
values, although there was a tendency 
for more recent A 14 C values to be found 
in the older cores, suggesting limited contamination. 
The second assumption is implicit in all ageing stud- 
ies, because it implies that a given growth increment 
is interpreted in the same way, whether observed in 
a young or an old fish. However, the third assump- 
tion, that of synchronicity among all North Atlantic 
14 C chronologies, is more interesting. This assump- 
tion has been tested and found to hold in all 14 C 
