60 
Fishery Bulletin 108(1 ) 
Table 1 
Stomach contents of large medium (185.4-205.7 cm curved fork length [CFL]) Atlantic bluefin tuna ( Thunnus thynnus ) caught off 
Cape Lookout, North Carolina, during Dec. 2003-Jan. 2004, Dec. 2004-Jan. 2005, and Dec. 2005-Jan. 2006. Diet is presented 
as percent frequency of occurrence (%0) and percent prey weight (%W). 
Dec. 2003- 
Dec. 2004- 
Dec. 2005- 
Jan. 2004 
Jan. 2005 
Jan. 2006 
Pooled years 
Prey item 
%0 %W 
%0 %W 
%o %W 
%0 
%W 
Chordata 
Brevoortia tyrannus 
76.92 89.41 
96.88 98.97 
82.61 96.43 
91.00 
98.42 
Menticirrhus littoralis 
4.35 1.45 
1.00 
0.24 
Mugil cephalus 
1.56 0.69 
1.00 
0.57 
Pomatomus saltatrix 
1.56 0.17 
1.00 
0.14 
Strongylura marina 
4.35 0.13 
1.00 
0.02 
Unidentified fish remains 
30.77 6.78 
4.69 0.05 
13.04 0.33 
10.00 
0.19 
Crustacea 
Ovalipes sp. 
4.35 0.19 
1.00 
0.03 
Portunus gibbesii 
1.56 0.02 
1.00 
0.01 
Portunus spinimanus 
1.56 0.05 
4.35 0.28 
2.00 
0.09 
Portunus spp. 
4.35 0.04 
1.00 
0.01 
Unidentified crab 
7.69 1.91 
1.56 0.01 
4.35 0.04 
3.00 
0.04 
Mollusca 
Loligo pealeii 
1.56 0.04 
8.70 1.11 
1.00 
0.03 
Unidentified squid 
7.69 0.02 
3.00 
0.18 
Protista 
Unidentified algae 
15.38 1.87 
2.00 
0.03 
Total prey biomass (kg) 
1.45 
83.04 
16.37 
100.86 
Total stomachs sampled 
14 
80 
30 
124 
Stomachs with prey (%) 
13(92.9) 
64 (80.0) 
23 (76.7) 
100 (80.6) 
Empty stomachs (%) 
1 (7.1) 
16(20.0) 
7(23.3) 
24 (19.4) 
Mean length of bluefin tuna (cm 
198.57 
194.59 
197.18 
195.66 
Standard error 
1.27 
0.62 
1.14 
0.52 
Mean weight of bluefin tuna (kg 
119.02 
108.66 
113.03 
110.89 
Standard error 
2.89 
1.72 
3.03 
1.40 
When examined by %W, diets were almost always 
dominated by Atlantic menhaden (Fig. 1, D-F and Fig. 
2, D-F). The only exception was the 1-14 December 
2005 within-winter period when Atlantic needlefish 
accounted for approximately 60% of diet by weight for 
giant tuna. When pooled, diets varied little between 
winters (for either large medium or giant bluefin tuna) 
or between size classes (Figs. IF and 2F). 
Gastric evacuation rates and daily ration 
During winter in North Carolina, large medium and 
giant bluefin tuna appear to feed predominantly during 
diurnal time periods (Fig. 3, A and B). A small number 
of fish were caught on trolled baits several hours before 
sunrise, and those stomachs collected during presun- 
rise hours were typically empty or contained food in 
the final stages of digestion (e.g., scales, bones, eye 
lenses, and pyloric stomachs of Atlantic menhaden), 
indicating that digestion occurred throughout the night 
and that feeding had not resumed until just before 
sunrise. Sample sizes for each size class were largest 
after sunrise (approximately 0700 EST) and remained 
high throughout the morning as gut fullness increased. 
Large medium bluefin tuna reached maximum gut full- 
ness between 1200 and 1300 EST (time point zero on 
Fig. 3A). The estimate of GER (±standard error [SE] ) 
for the large medium bluefin tuna size class was 0.13 
±0. 05/hr. Giant bluefin tuna attained a maximum gut 
fullness between 1300 and 1400 EST (time point zero 
on Fig. 3B), and had a GER (±SE) of 0.12 ±0. 04/hr. The 
confidence interval of GER di ^ erence contained the value of 
zero, and therefore there was no significant difference 
between GER large medlum and GER giant . Thus, a combined 
(large medium and giant) GER value (Fig. 30 was used 
to estimate DR. The GER (±SE) was 0.12 ±0. 03/hr for 
the combined analysis (Fig. 3C). 
The mean (±SE) DR estimate of bluefin tuna in NC 
was 2.03% ±0.59. When multiplied by the mean weight 
of bluefin tuna collected during our study, the absolute 
daily consumption by an individual bluefin tuna in 
North Carolina during winter was 3.18 kg/day. 
