Biology and fishery of the bullet tuna, Auxis rochei (Risso, 1810) in Indian waters

Abstract

Auxis rochei, popularly known as the bullet tuna, is the smallest of all tuna species available in Indian waters. Its distribution is reported from all maritime states but it forms a fishery of commercial importance only in the south-west region (Kerala, Tamil Nadu and Karnataka) with targeted fishery being carried out in southern Kerala. The average annual catch (2006- 2010) is estimated at 3,131 t, constituting 2.8% of the total tuna landings. Commercial exploitation is mainly by gillnets and small hook and lines with the 0-1 yr old fishes comprising bulk of the commercial catch. The length-weight relationship was estimated as W=0.0076L3.249 with no significant difference between the sexes. Size at first maturity was estimated at 23.6 cm and fecundity estimated was 12,03,258. A. rochei spawns throughout the year with peak during July-September. Zooplankton, fishes and crustaceans were the dominant food items recorded. The von Bertalanffy growth parameters estimated were L∞= 42.3 cm, K= 0.61 yr-1 and t0= -0.0337. Mortality estimates were M=1.18 and Z=5.90 and F=4.72 with a high exploitation rate of E=0.80, calling for appropriate management measures to be adopted for continued exploitation at sustainable levels.