Feature article

Correlation of ENSO (illustrated by the SOI) variations to skipjack tuna catch rate (metric tonnes per day) and catch location indicates displacements in tuna populations are related to the eastern edge of the western Pacific warm pool movements.

Climate change impacts on Pacific tuna fisheries

Dr. Andrew Lorrey, National Institute of Water and Atmospheric Research, New Zealand

Climate change will likely affect Pacific Ocean fisheries through raising ocean surface temperatures and through increased inter-annual climate variability. Direct impacts of climate change are anticipated to affect the distribution of key commercial fish species in the Pacific, as well as their abundance and catchability, including tuna.

Tuna fisheries in the Pacific

Nearly 70% of the world’s tuna harvest comes from the Pacific Ocean. At present, 3.2 million tonnes are harvested from this region, and the catch is comprised mostly of skipjack tuna. Catches are highest in the western equatorial Pacific warm pool, which is characterised by low production rates and comprise the warmest surface waters of the world’soceans. This warm pool is fundamental to the El Niño-Southern Oscillation (ENSO) and the Earth’s climate in general.

Changes in primary productivity

A decline in central and eastern Pacific primary productivity due to increased stratification between warm surface waters and colder deep water would reduce upwelling. This would result in a spatial redistribution of tuna resources to higher latitudes and toward the western equatorial Pacific. A decline in bigeye and adult yellowfin tuna populations might occur as a result of changes in primary productivity with possible impacts on the species targeted by longline fishing fleets. With an increased demand for sashimi and high quality fish world-wide, pressure on yellowfin tuna is expected to rise to compensate for decreased catch of bigeye tuna, and could potentially lead to an unsustainable population if the fish stocks are not well managed. However, the productivity rise anticipated for the western Pacific might help offset this pressure, and a catch of one million tonnes of skipjack tuna per year is deemed sustainable. Central Pacific countries like Kiribati that have a highdependence on tuna fishing makes them and their domestic fishing fleets most vulnerable to the climate change impacts on fish populations that may occur in the near future.

Future climate change and tuna fishing

Large uncertainties about the changes in western equatorial Pacific productivity mean there are many questions about climate change impacts on spawning migrations for tuna as well as the connections these fisheries have with extra-tropical regions.

Current research programmes like the Oceanic Fisheries and Climate Change Project (OFCCP) are underway to critically assess climate change impacts on oceanic tunastocks with the aim of predicting short- to long-term population variations that will occur with global warming and increased climate variability. It is anticipated that this will help us understand how greenhouse warming will affect the abundance and productivity of commercially exploited species and fisheries at both the oceanic and global scale.

Information for this article was sourced from the Secretariat of the Pacific Communities Oceanic Fisheries Programme (New Caledonia) and The World Bank.