El Nino Southern Oscillation and tuna in the western Pacific

Nearly 70% of the world's annual tuna harvest, currently 3.2 million tonnes, comes from the Pacific Ocean. Skipjack tuna (Katsuwonus pelamis) dominate the catch. Although skipjack are distributed in the surface mixed layer throughout the equatorial and subtropical Pacific, catches are highest in the western equatorial Pacific warm pool, a region characterized by low primary productivity rates' that has the warmest surface waters of the world's oceans (Fig. 1). Assessments of tuna stocks indicate that recent western Pacific skipjack catches approaching one million tonnes annually are sustainable(2). The warm pool, which is fundamental to the El Nino Southern Oscillation (ENSO) and the Earth's climate in general(3-5), must therefore also provide a habitat capable of supporting this highly productive tuna population. Here we show that apparent spatial shifts in the skipjack population are linked to large zonal displacements of the warm pool that occur during ENSO events(5,6). This relationship can be used to predict (several months in advance) the region of highest skipjack abundance, within a fishing ground extending over 6,000 km along the Equator.