Age and growth, mortality and stock assessment of Euthynnus affinis (Cantor) from Maharashtra waters

Kawakawa, Euthynnus affinis contributed on an average 1,563 t to the annual fish landings during 1996-2000 in Maharashtra. The drift net is the major gear, which exploits tuna resource. The species form about 87 % of the tuna landings by drift net at Sassoon dock (Mumbai). The other species were Thunnus tonggol, Auxis thazard and A. rochei, which together constituted about 13.0 % of the drift gill net catch. The size range of E. affinis in the drift net was from 26 to 73 cm. The growth parameters estimated are L ∝= 81.7 cm and K = 0.79 (annual). The total mortality coefficient (Z) varied between 2.04 and 2.88 dur- ing 1996-2000 with an average of 2.24 during the last 3 years with exploita- tion ratio (F/Z) of 0.6. The natural mortality coefficient (M) has been estimated as 0.928. The biomass is 1,344 t off Maharashtra, while the present average yield is 1,722 t. The maximum sustainable yield (MSY) has been estimated as 1,725t for Maharashtra indicating that the present exploitation is close to MSY