185 
Abstract .—Radiocarbon ( 14 C) in the 
world’s oceans increased sharply be- 
tween 1950 and 1970 as a result of the 
atmospheric testing of nuclear weap- 
ons. Through comparison with the 14 C 
time series reconstructed from atmo- 
spheric measurements and marine car- 
bonates, Kalish, in 1993, used the 14 C 
concentration measured in fish otolith 
cores as a means of confirming the an- 
nulus-based age estimates for some 
South Pacific fish species. Here we re- 
port the pre- and postbomb 14 C chro- 
nology of North Atlantic adult black 
drum (Pogonias cromis), assumed to be 
between 15 and 42 yr of age on the ba- 
sis of otolith annulus counts. According 
to accelerator mass spectrometry 
(AMS) assays, 14 C in otolith cores in- 
creased sharply between 1958 and 
1964, with a timing and magnitude 
which was very similar to that of the 
atmospheric bomb 14 C signal. The cor- 
respondence between the two 14 C chro- 
nologies indicates that the annulus- 
based age assignments were accurate 
on average to within 1-3 yr. Differences 
between the black drum A 14 C chronol- 
ogy and that of other marine carbon- 
ates in the North Atlantic are explained 
by the estuarine habitat of young-of- 
the-year black drum and by the fact 
that estuarine A 14 C values more closely 
reflect atmospheric values than surface 
ocean values. At present, there is no 
other age-validation technique that can 
confirm the absolute age of long-lived 
fish species with comparable levels of 
accuracy. 
Manuscript accepted 18 August 1997. 
Fishery Bulletin 96: 185-192 (1998). 
Radiocarbon from nuclear testing 
applied to age validation of 
black drum, Pogonias cromis 
Steven E. Campana 
Marine Fish Division, Bedford Institute of Oceanography 
RO. Box 1006, Dartmouth 
Nova Scotia, Canada B2Y 4A2 
E-mail: campanas@mar.dfo-mpo.gc.ca 
Cynthia M. Jones 
Applied Marine Research Laboratory and 
Department of Biological Sciences 
Old Dominion University 
Norfolk, Virginia 23529-0456 
Despite the international accep- 
tance of otolith annuli as the best 
means for estimating the age of 
most fish species, the correct inter- 
pretation of annuli is far from easy 
and can result in serious and sys- 
tematic ageing errors (Beamish and 
McFarlane, 1995). Indeed, aside 
from the use of tagged, hatchery- 
reared fish released into the wild, 
confirmation of the accuracy of a 
method of annulus interpretation 
for marine fish species is often prob- 
lematic. Mark-recapture of chemi- 
cally tagged individuals has gener- 
ally been considered to be the most 
accurate means of confirming the 
frequency of formation of presumed 
annuli, owing to a correspondence 
between time at liberty and the 
number of annuli distal to the 
chemical check (Foreman, 1996). 
Although the approach is sound, 
extremely low recapture rates for 
fish at liberty more than 2-3 years 
can make it difficult to acquire suf- 
ficient samples for an adequate test. 
Moreover, the technique validates 
the time elapsed since tagging, not 
the absolute age of the fish. Alter- 
natively, radiochemical dating 
based on 210 Pb: 226 Ra or 228 Th: 228 Ra 
ratios can be used to differentiate 
between very different age interpre- 
tations (Bennett et al., 1982; Cam- 
pana et al., 1990), but these assays 
are too imprecise for detailed or in- 
dividual age confirmations. The 
most widely used approach, that of 
the seasonal progression of mar- 
ginal increments (Beckman and 
Wilson, 1995) is well suited only to 
fast-growing fish and suffers from 
the lack of an objective means of 
evaluation. Thus there is a well-de- 
fined gap in our ability to confirm 
the age interpretations of the ma- 
jority of marine fish species, particu- 
larly those that are long-lived. How- 
ever, the recent finding that nuclear 
testing left a dated mark in the 
otolith (Kalish, 1993) provides a sig- 
nificant breakthrough in our abil- 
ity to determine accurate, absolute 
ages for individual long-lived fish. 
Kalish ( 1993) was the first to de- 
scribe the use of bomb radiocarbon 
( 14 C or carbon- 14 ) as a dated marker 
in fish otoliths and its value for con- 
firming age interpretations. His 
findings were based on earlier work 
that had documented a 100% in- 
crease in atmospheric radiocarbon 
as a result of the widespread atmo- 
