Feeding partitioning among tuna taken in surface and mid-water layers: the case of yellowfin (Thunnus albacares) and bigeye (T. obesus) in the Western Tropical Indian Ocean
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The trophic relations of two apex predators, yellowfin and bigeye tuna (Thunnus albacares and T. obesus), and their prey were investigated in the western tropical Indian Ocean. The contents of 173 non-empty stomachs were analysed from specimens caught with longlines and purse seine during scientific and fishing cruises. Diet data were processed by occurrence, by number, and by wet weight and a comparison of diets between surface and deep swimmers made. Crustaceans were the almost exclusive food source of surface-swimming bigeye tuna, with the stomatopod (Natosquilla investigatoris) being the sole prey item recorded in this category. The diet of deep-swimming yellowfin tuna was balanced between epipelagic fish, crustaceans and cephalopods. Bigeye tuna fed predominantly on cephalopods and mesopelagic fish (Scopelarchidae and Paralepididae), for which this predator appeared to be the most active chaser. The diet of the two predators reflects their ability to catch the prey, and their vertical distribution.