Diet composition and feeding habits of yellowfin tuna Thunnus albacares (Bonnaterre, 1788) from the Bay of Bengal

Abstract

Though yellowfin tuna (Thunnus albacares) is one of the important fishery resources in the Bay of Bengal, knowledge on its ecology, diet composition and feeding habits are limited from this area. In view of that, present study focuses on the diet composition and feeding habits of yellowfin tuna (YFT) hooked during exploratory longline survey conducted in the Indian EEZ of the Bay of Bengal during 2019–2021. A total of 213 specimens in the length range of 42.0 to 171.0 cm fork length (FL) were examined, of which 28.2% were empty while the remaining 71.8% contained at least one prey item. The modified Costello graphical method shows a wide range of prey items, with a few prey species that are dominant and can be found in high densities in the Bay of Bengal. Due to the fact that this apex predator is a generalist feeder, this might be the case. Cluster analysis based on the %IRI (Index of relative importance) identified two size groups. YFT with smaller (<80 cm FL) is one group. Crustaceans was the most frequently eaten prey in that group followed by cephalopods and teleostea. The second group consists of two length groups medium (81–120 FL), and larger (>120 FL), Cephalopods were the dominant prey items of this group and accounts for 62.0% in %IRI followed by teleostea 31.3% of the diet. Cephalopods (Sthenoteuthis oualaniensis) were the primary food consumed in all the size groups, followed by crustaceans (Charybdis smithii) and Teleost fishes (Cubiceps pauciradiatus). The dietary breadth and the occurrence of empty stomachs were significantly related to size of the yellowfin tuna. With increasing body size, diet breadth gradually increased while the percentage of empty stomachs declined. The yellowfin tuna diet does not vary significantly during the seasons. However, cephalopods were found in 53.5% of the IRI in their diet. Furthermore, there were notable seasonal changes in the percentage of empty stomachs, with the highest percentage observed during the monsoon season (38.3%).