Population Dynamics of Yellowfin Tuna Thunnus albacares (Bonnaterre, 1788) in the Fisheries Management Area 573 of the Indian Ocean

Abstract

Yellowfin tuna Thunnus albacares is one of the major species of tuna caught in the Fisheries Management Area (FMA) 573 of the Indian Ocean. Its production contributed to 35.83% of the total production of tuna in 2013. The study was conducted to assess the population dynamics of this species in FMA 573, based on length-frequency data collected in 2013-2017, and was analysed using FiSAT II software. The results obtained show length-weight relationship of W = 0.000052 FL^2.78, negative allometric growth and growth equation of Lt = 194.25 (1-e^{-0.51 (t + 0.1889)}). The length at first capture was estimated at 140 cm FL. Recruitment season occurs between July and September, with a peak in August. The rate of total mortality (Z) was 2.32 yr^-1, including natural mortality rate (M) of 0.69 yr^-1 and fishing mortality rate (F) of 1.63 yr^-1. The exploitation rates of yellowfin tuna were estimated to be 0.70, indicating that it has exceeded the optimum exploitation rate (E = 0.5) and that overexploitation had occurred. There is an obvious need for consistent monitoring and surveillance of fishing fleet, type and size of fishing gear, as well as the fish size and quantity of the catch.