Butler et al.: Feeding ecology of Thunnus thynnus in North Carolina 
63 
1 1 Brevoortia tvrannus 
WMM Cephalopoda 
Y////X Rivalvia 
V////y//h Strongylura marina 
llllllllllll Teleosts 
1 1 1 1 1 1 Prolisla 
Portunidae 
1 1 Misc. fish 
Figure 1 
Stomach content composition of large medium Atlantic bluefin tuna (Thun- 
nus thynnus) examined by using relative percent frequency of occurrence 
(A-C) and percent prey weight (D-F). Stomachs were collected from fish 
captured near Cape Lookout, North Carolina, during December-Janu- 
ary 2004-05 (A and D), December-January 2005-06 (B and E), and 
pooled years (C and F). Frequency of occurrence data are normalized 
to 100%. 
We regularly observed squid (Loligo spp.) and portu- 
nid crabs in bluefin tuna stomachs. Squid has been sug- 
gested as the second-most important prey item, behind 
teleosts, in several bluefin tuna diet studies (Dragovich, 
1970; Eggleston and Bochenek, 1990; and Kade, 2000). 
Portunid crabs have previously been documented by 
Kade (2000), and authors such as Krumholz (1959), 
Dragovich (1970), and Chase (2002) have found minor 
amounts of crustaceans in the diet of bluefin tuna of 
various size classes and at various locations. The inclu- 
sion of cephalopods and crustaceans at certain times of 
the year may be a result of increases in their relative 
abundance. Juanes et al. (2001) found this to be the ex- 
planation for bluefish, a primary piscivore that included 
invertebrate prey in its diet when invertebrates were 
relatively abundant in the environment. No quantitative 
information exists on the distribution and abundance 
of potential prey. Thus, we were unable to make any 
conclusions about prey-type selectivity. 
Gastric evacuation and daily ration 
Bluefin tuna in North Carolina were caught from approx- 
imately two hours before sunrise to late afternoon or 
evening. Time of catch could match bluefin tuna feed- 
ing periods or could be an artifact of fishing times. 
