62 
Fishery Bulletin 108(1 ) 
Table 3 
Results from randomized cumulative prey curves for large medium and giant bluefin tuna ( Thunnus thynnus) collected off 
Cape Lookout, North Carolina, during the 2004-05 and 2005-06 season. Values in bold indicate sufficient sample sizes to 
describe bluefin tuna diet at a=0.05. Sample sizes ( n ), sampling statistics ( t ), and P-values are presented. 
Large medium 
n 
t 
P-value 
Giant 
n 
t 
P-value 
2004-05 
2004-05 
1-14 Dec. 
20 
56.003 
<0.001 
1-14 Dec. 
16 
2.152 
0.164 
15-31 Dec. 
40 
5.061 
0.037 
15-31 Dec. 
57 
4.042 
0.056 
1-31 Jan. 
4 
5.590 
0.031 
1-31 Jan. 
27 
3.839 
0.062 
Pooled data 
64 
0.965 
0.435 
Pooled data 
100 
2.541 
0.126 
2005-06 
2005-06 
1-14 Dec. 
8 
8.914 
0.012 
1-14 Dec. 
24 
3.891 
0.060 
15-31 Dec. 
10 
20.350 
0.002 
15-31 Dec. 
87 
2.460 
0.133 
1-31 Jan. 
5 
6.699 
0.022 
1-31 Jan. 
26 
10.298 
0.009 
Pooled data 
23 
3.888 
0.060 
Pooled data 
137 
-0.440 
0.703 
Table 4 
Chi-square values for comparisons of the effects of within-winter, year, 
and size class on dietary composition of Atlantic bluefin tuna (Thunnus 
thynnus) collected off Cape Lookout, North Carolina, during 2004-05 and 
2005-06 as determined by RxC tests of independence (Sokal and Rohlf, 
1981) of frequency (count) data. Degrees of freedom were calculated as 
(rows-D(columns-l). Within-winter time periods (Dl=l-14 December; 
D2=15-31 December; and J=l-31 January) and years were compared 
for each size class (large medium and giant tuna) from both years. The 
total number of nonempty stomachs analyzed for each comparison is given 
within parentheses. 
Groups compared 
X 2 value 
Degrees 
of freedom 
P-value 
Within-winter 
Large medium tuna 
D1/D2/J 2004-05 (64) 
10.864 
10 
0.210 
D1/D2/J 2005-06 (23) 
11.140 
10 
0.347 
Giant tuna 
D1/D2/J 2004-05 (100) 
16.182 
14 
0.303 
D1/D2/J 2005-06 (137) 
51.976 
14 
<0.001 
Year 
Large medium tuna 
2004-05/2005-06(87) 
9.570 
5 
0.088 
Giant tuna 
2004-05/2005-06(237) 
19.736 
8 
0.011 
Size class 
Large medium /Giant (352) 
15.637 
8 
0.048 
bluefin tuna population fell within the 
ranges of predatory demand of these other 
predators (Fig. 5). None of the consump- 
tion estimates of natural Atlantic men- 
haden predators approached the annual 
harvest from the commercial fishery. 
Discussion 
Importance of Atlantic menhaden 
to bluefin tuna 
Atlantic menhaden was the primary prey 
for both large medium and giant bluefin 
tuna during multiple winters in North 
Carolina; this focus on a single prey type 
is unusual for a marine apex predator. 
Although other prey were frequently pres- 
ent (e.g., portunid crabs), they contrib- 
uted little in terms of biomass. With the 
exception of Kade (2000), Atlantic menha- 
den has not been considered a dominant 
prey of bluefin tuna along the U.S. East 
Coast (Chase, 2002). Kade’s (2000) result 
for 1999 and now our results for subse- 
quent years have confirmed that blue- 
fin tuna are a consistent and potentially 
important predator of Atlantic menhaden 
during winter. Although these are the 
first quantitative studies to identify this 
predator-prey linkage, historic anecdotal 
information described bluefin tuna feeding on schools 
of Atlantic menhaden off New England in the 1800s 
(Goode, 1879). 
The composition of bluefin tuna diet depends on prey 
availability and predator body size (Chase, 2002). In 
North Carolina, diets of large medium and giant blue- 
fin tuna were dominated by Atlantic menhaden. Thus, 
there was no shift in diet with the increase in bluefin 
tuna length. Chase (2002) reviewed previous bluefin 
tuna diet studies and came to the conclusion that the 
diet of bluefin tuna from any particular study location is 
dominated by “a single, pelagic, schooling prey species.” 
Atlantic menhaden appear to match this prey descrip- 
tion during winter in North Carolina. 
