Fishery, biology and population characteristics of frigate tuna Auxis thazard (Lacepede, 1800) from Indian waters

The frigate tuna, Auxis thazard forms a coastal fishery in India throughout the year. Duringthe period 2015-2020, with an annual average catch of 6,387 t, the resource formed 7.14%of the total tuna catch of the country. Andhra Pradesh (1,131 t) recorded the maximumlandings followed by Karnataka (968 t) and Tamil Nadu (701 t). In West Bengal and Odisha,A. thazard formed more than 60% of the total tunas landed. Mature fishes dominated inJanuary-March. Size at first maturity was 31.9 cm TL. Size (fork length) was in the range22.8-68 cm and the estimated length-weight relationship was log W = 0.000049 + 3.1740log L (n = 832, r2= 0.93) (95% CI). The von Bertalanffy growth equation derived was: Lt = 72.61 - e -0.73 (t + 0.063). The growth performance index was 3.585 and the length at first capture wasestimated at 33.35 cm. The estimated natural mortality, fishing mortality and total mortalitywere 1.17, 1.21 and 2.38 respectively; the exploitation rate was 0.508. Emax estimated was0.735, which is higher than the present levels, indicating scope for further exploitation. Theprediction analysis for MSY, F/Fmsy and B/Bmsy showed the current exploitation is sustainable,indicating scope for increasing catch with increased effort. Keywords:Fishery biology, Population dynamics, Thompson andBell, VPA