Ganachaud, A., A. Sen Gupta, J. N. Brown, K. Evans, C. Maes, L. C. Muir, et F. S. Graham
Projected changes in the tropical Pacific Ocean of importance to tuna fisheries
Submitted to Climatic Change
Future physical and chemical changes to the ocean can significantly affect the distribution and productivity of marine species. Tuna are of particular importance in the tropical Pacific, because they contribute significantly to the livelihoods, food and economic security of island states. Changes in water properties and circulation will impact on tuna larval dispersal, preferred habitat distributions and the trophic systems that support tuna. Using observations and ocean projections from the CMIP3 and preliminary results from CMIP5 climate models, we document the projected changes to ocean temperature, salinity, stratification and circulation most relevant to current distributions of tuna. Under a business-as-usual emission scenario, projections indicate surface intensified warming in the upper 400m and a large expansion of the Pacific Warm Pool, with most surface waters of the central and western equatorial Pacific reaching temperatures warmer than 29°C. These changes are likely to alter the preferred habitat of tuna, based on present-day thermal tolerances, and in turn the distribution of spawning and foraging grounds. Large-scale shoaling of the mixed layer and increases in stratification are expected to impact nutrient provision to the biologically active layer, with flow-on trophic effects on the micronekton. Several oceanic currents are projected to change, including an increased equatorial undercurrent flow, which could modify the supply of bioavailable iron to the eastern Pacific.