Neritic tuna with special reference to the fishery and biology of Thunnus tonggol in the Indian Waters

Abdul Azeez, P and Abdussamad, E M and Mohammed Koya, K and Rajesh, K M and Surya, S and Kizhakudan, Shoba Joe and George, Grinson (2025) Neritic tuna with special reference to the fishery and biology of Thunnus tonggol in the Indian Waters. Discussion Paper. Food and Agriculture Organization.

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Abstract

The neritic tuna fishery of India is supported by five key species: longtail tuna (Thunnus tonggol), kawakawa, striped bonito, bullet tuna, and frigate tuna. These species are of high economic value and provide significant livelihood support, especially to the coastal states. They are exploited by mechanized, motorized, and non-mechanized fishing units operating within the Indian Exclusive Economic Zone (EEZ), primarily along the continental shelf. Gillnetters are the primary gear targeting larger individuals of this group. The total tuna catch in Indian waters shows a steady increase between 1995 (37,789 t) and 2024 (120342 t), with neritic tunas consistently dominating over oceanic tunas. Neritic tunas contributed 51–65% to the total tuna catch in India, Euthynnus affinis remained the dominant species, accounting for nearly 63.5% of the neritic tuna catches followed by Auxis spp. (29.1%), Thunnus tonggol (6.4%) and Sarda orientalis (0.9%) (563 t). Thunnus tonggol (longtail tuna) is widely distributed along the Indian mainland coast and the Andaman and Nicobar Islands. However, its fishery is particularly significant along the northwest coast, accounting for 97.83% of the national longtail tuna catch. During the study period, annual landings of T. tonggol varied from 4,195 tonnes (2020) to 6,537 tonnes (2024), averaging 3,909 tonnes. Length measurements of T. tonggol specimens ranged from 34.0 cm to 94.5 cm, with a mean length of 58.7 cm. The growth parameters, L∞ and K were 91.18 cm and 0.2 year-1 respectively. The size at first capture (Lc) was 62.27 cm. The growth performance index was 3.22 and t_anchor 0.64. The estimated mortality rates M, F and Z were 0.457, 0.464 and 0.921 respectively. The F/M was 1.015 and exploitation rate was 0.504, indicating fishery is sustainable. The observed sex ratio (male:female) was 1:2.11, indicating a strong dominance of females. The estimated length at which 50% of fishes attained sexual maturity was 67±0.52 cm total length and average fecundity was estimated at 3,11,433 numbers. The diet comprised mainly of fishes (61.92%), shrimps(18.51%), cephalopods (15.67%), partially digested materials (2.44%), squilla (1.37%) and crabs (0.08%), based on Index of Relative Importance (IRI).

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