El Niño 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 rates1 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 sustainable2. The warm pool, which is fundamental to the El Niño Southern Oscillation (ENSO) and the Earth's climate in general3,4,5, 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 events5,6. 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. Figure 1 Distribution of skipjack tuna catch (tonnes) and mean sea surface temperature (SST, in °C) in the Pacific Ocean. a, In the first half of 1989 (La Niña period). b, In the first half of 1992 (El Niño period). The effect of ENSO on the location of the warm pool (SST > 28–29 °C) and the distribution of skipjack catch is clearly evident.