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Fishery Bulletin 96(2), 1 998 
two. Therefore, all age and year-class estimates were 
based on annulus counts along the ventral aspect of 
the core-medial axis. 
The assay results for mean 8 13 C were consistent 
with those observed previously in fish otoliths (mean 
± SD=-3.48±1.50%o) (Table 1). Although the presence 
of a slight but significant decrease across years (b~ 
-0.09, P=0.04, r 2 =0.13) was somewhat larger than 
the long-term ocean trend reported by Quay et al. 
(1992) and was of different slope than that reported 
for North Atlantic haddock otoliths (Campana, 1997), 
the biological significance of the observed trend is 
questionable given the relatively large coefficient of 
variation (CV=43%) among the samples. In contrast, 
A 14 C differed strongly and systematically though 
time; concentrations were relatively low and constant 
prior to the late 1950’s but increased sharply to a 
peak in the mid-1960’s (Table 1; Fig. 2). Subsequent 
values continued to decline to the end of the time 
Table 1 
Summary of A 14 C and 8 13 C assay results for each black 
drum otolith core. 
Annulus 
Year class 
age (yr) 
a 14 c 
SD 
5 13 C 
1948 
42 
-38.8 
5.9 
-0.9 
1950 
40 
-78.2 
8.3 
-2.7 
1952 
38 
-36.7 
6.4 
-2.4 
1954 
36 
-71.9 
5.9 
-5.9 
1954 
36 
-62.8 
6.1 
-2.1 
1957 
33 
1.9 
4.6 
-2.7 
1958 
32 
45.2 
7.8 
-2.2 
1959 
31 
-3.1 
6.4 
-3.0 
1959 
31 
101.9 
7.2 
-1.9 
1960 
30 
46.1 
6.8 
-3.3 
1960 
30 
18.1 
6.6 
-4.3 
1960 
30 
70.8 
6.8 
-1.9 
1961 
29 
175.3 
7.5 
-3.3 
1962 
28 
62.4 
4.5 
-5.9 
1962 
28 
182.5 
7.5 
-4.4 
1963 
27 
299.3 
8.5 
-0.8 
1963 
27 
136.2 
7.3 
-2.6 
1963 
27 
95.7 
7.1 
-5.8 
1964 
26 
111.4 
6.8 
-6.0 
1964 
26 
194.2 
7.6 
-2.3 
1964 
26 
371.4 
9.1 
-4.8 
1965 
25 
340.6 
8.6 
-4.4 
1965 
25 
106.4 
7.1 
-4.9 
1966 
24 
366.5 
9.1 
-4.4 
1967 
23 
291.1 
8.5 
-3.3 
1968 
22 
297.2 
10.2 
-2.9 
1968 
22 
261.8 
8.2 
-2.9 
1968 
22 
207.5 
8.0 
-3.2 
1970 
20 
213.1 
7.8 
-2.4 
1973 
17 
255.2 
8.1 
-4.0 
1975 
15 
150.4 
6.5 
-6.3 
series in 1975. The maximum rate of increase oc- 
curred between 1958 and 1964 and was easily differ- 
entiated from the adjacent time periods. Therefore, 
the A 14 C of the cores of the black drum otoliths was 
characteristic of the period of incorporation and could 
reasonably be considered a dated marker. 
The A 14 C from the otolith cores from the prebomb, 
pre-1957 year classes (-57.7±19.0%c) was very simi- 
lar to that which has been measured in other North 
Atlantic otoliths, corals, and bivalves (Fig. 3). How- 
ever, considerably more 14 C was incorporated into 
black drum otoliths during the 1960’s than has been 
measured in most other marine carbonates. Indeed, 
peak A 14 C values in black drum (-340%©; Fig. 2) were 
almost twice as high as those recorded in contempo- 
raneous corals, and almost four times as high as those 
measured in haddock otoliths of the same year 
classes. After normalizing the black drum and ma- 
rine carbonate time series to the same scale, the black 
drum A 14 C chronology appeared to both begin its in- 
crease and reach a peak approximately 2-3 yr be- 
fore that of the other carbonates. In addition, unlike 
the A 14 C in the other taxa, the A 14 C in the black drum 
otoliths declined significantly (to +150%e in 1975) 
after reaching a peak in the mid- 1960’s. Thus in terms 
of phase coherence, peak magnitude, and subsequent 
decline, the black drum A 14 C chronology more closely 
resembled that of the atmosphere than of other ma- 
rine carbonates. 
To assess the level of correspondence between the 
black drum A 14 C chronology and that of the atmo- 
sphere, the two time series were scaled to compa- 
rable magnitudes. The resulting correspondence was 
striking (Fig. 4), both in its rate of increase and sub- 
sequent decline. The phase shift between the two chro- 
nologies was approximately 1 yr, with black drum lag- 
ging behind atmosphere. 
Discussion 
In light of the sharp rate of increase of the 14 C signal 
associated with the onset of nuclear testing, inter- 
pretation of the 14 C chronology in otolith cores is rela- 
tively simple; the otolith chronology should match 
other published chronologies for the region as long 
as the annular age assignments (=year class) are 
correct. Any under-ageing would phase-shift the 
otolith 14 C chronology towards more recent years, 
whereas over-ageing would phase-shift it towards 
earlier years. Because marine waters with A 14 C val- 
ues greater than 0 %c did not generally exist prior to 
the late 1950’s, coastal fish otolith cores with sub- 
zero values must have formed before the late 1950’s. 
Contamination with material of more recent origin 
