Trophic segregation of mixed schools of yellowfin tuna (Thunnus albacares) and skipjack tuna (katsuwonus pelamis) caught in the eastern tropical Pacific Ocean

One of the major challenges in trophic ecology is to understand how organisms interact with each other and to apply this knowledge to the management of populations, communities and ecosystems. Our goal was to examine fine-scale variability in the feeding habits and trophic position of yellowfin tuna (Thunnus albacares) and skipjack tuna (Katsuwonus pelamis) caught together in mixed schools by purse seine to examine the null hypothesis that the association between these 2 tuna species is not related to trophic interactions. In total, 439 yellowfin tuna and 216 skipjack tuna were collected in 3 different areas in the eastern tropical Pacific Ocean during 2005. The stomachs of both tuna species contained prey at different stages of digestion, which indicated intermittent feeding throughout the course of the day. Yellowfin tuna consumed mainly epipelagic crustaceans and mesopelagic squids, whereas epipelagic euphausiids and epipelagic flyingfish were the most abundant prey species in the stomach contents of skipjack tuna. Our results suggested that both tuna species employed an opportunistic predation strategy, but significant dietary differences showed that they occupy different trophic levels, and that there is no food competition between yellowfin and skipjack tunas in the eastern tropical Pacific Ocean.