Alatorre-Ramirez et al.: Trophic segregation of mixed schools of Thunnus albacares and Katsuwonus pelamis 
261 
112 12 
100 
80 
i 60 
40 
20 
0 
B 
100 
80 
_ 60 
cr 
40 
20 
Morning Afternoon Evening 
§ Auxis spp. H Vinciguerria lucetia 
S Cubiceps spp. ^ Dosidicus gigas 
Q Harengula thrissina HU Lolignidae 
IS Pleuroncodes planipes 
Figure 3 
Variation in diet composition, determined 
with the relative importance index (%IRI), 
in relation to (A) size class (small, 1-85 cm 
in fork length [FL], and large, >85 cm FL), 
(B) months, and (C) capture time for yel- 
lowfin tuna {Thunnus albacares) caught in 
2005 in zone 1 in the eastern tropical Pa¬ 
cific Ocean. The numeral above each bar 
indicates the number of stomachs with 
contents. 
100 
90 
80 
70 
60 
E 
5 50 
40 
30 
20 
10 
0 
Oxyporhamphus micropterus 
Dosidicus gigas 
Auxis spp. 
Argonauta spp. 
Figure 4 
Variation in diet composition, determined with the relative impor¬ 
tance index (%IRI), in relation to month of capture for yellowfin 
tuna {Thunnus albacares) caught in 2005 in the zone 2 in the east¬ 
ern tropical Pacific Ocean. The numeral above each bar indicates 
the number of stomachs with content. 
7 
Small 
I I Vinciguerria Lucetia 
H Exocoetus volitans 
Large 
Figure 5 
Variation in diet composition, determined with the relative impor¬ 
tance index (%IRI), in relation to size class (small, 1-50 cm in fork 
length [FL], and large, >50 cm FL) of skipjack tuna {Katsuwonus 
pelamis) caught in 2005 in zone 3 in the eastern tropical Pacific 
Ocean. The numeral above each bar indicates the number of stom¬ 
achs with content. 
Panama lightfish make vertical migrations to the epipelagic area 
at night to feed (Olson and Boggs, 1986; Galvan-Magana, 1988). 
The presence of these prey species in the stomachs of yellowfin 
and skipjack tunas is likely the result of these movements into the 
epipelagic area where these tuna species forage. 
