The effects of ocean temperature gradients on bigeye tuna (Thunnus obesus) distribution in the equatorial eastern Pacific Ocean

Abstract The water temperature at 100-300 m depth layer impact on bigeye tuna distribution has been studied from data collected by 15 fishery survey vessels, surveying every day, in the Equatorial Pacific Ocean from February to March and June to September 2010. The in situ ocean temperature measurements at four depths (100, 150, 200, and 300 m), satellite data and TAO/TRITON moored buoy data were also augmented in this study. The results reveal stereoscopic temperature factors for the prediction of tuna fishing ground: horizontal temperature gradient (HTG), vertical temperature gradient (VTG) in the 100-300 m layer. Maximal catches were observed where 1) vertically there has a strong subsurface temperature front in the 150-200 m layer, with horizontal temperature gradient up to near 0.020°C/km; 2) there have vertical temperature gradient between -0.088 and -0.066°C/m. Meanwhile, the monthly tuna fishery catches decrease with the synchronized reduction of 20 °C isotherm depth in the ocean.