Diet composition and feeding ecology of mackerel tuna Euthynnus affinis (Cantor, 1849) on the South-Eastern coast of India

ABSTRACT

Tuna as apex predators play a significant role in epipelagic ecosystems but have not been well documented in India due to sampling difficulties posed by their migratory behaviour. During March 2016 to February 2017 we recorded the diet composition of 244 specimens of mackerel tuna, Euthynnus affinis, ranging from 26 to 59 cm in total length collected on the southeast coast of India. Gut analysis showed that almost 42% were well full of food and 30 were empty (vacuity index = 12%), varying significantly (p < 0.05) throughout the year. The diet mostly comprised crustaceans, molluscs and teleosts. The dominant prey items were Megalopa sp. (index relative of importance or IRI = 35%), alima larvae (IRI = 21%), and cephalopods (IRI = 8%). Prey size was the most significant factor influencing the composition of the diet. Large fishes (above 52 cm) fed primarily on teleosts, whereas medium sized fishes (30–48 cm) predominantly consumed crustacean and molluscan prey. Multivariate tree analysis revealed that prey items explained most of the variation in diet composition. There was high feeding similarity between sampling months. Based on the diet composition, mackerel tuna can be a considered a generalist predator.

KEYWORDS:

• Diet
• mackerel tuna
• Euthynnus affinis
• feeding ecology
• Indian waters

Acknowledgments

The authors gratefully acknowledge the help of professional fisherfolk in collecting material for this study.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was financially supported by Department of Science and Technology, Govt. of India (SB/SO/AS/063/2013).