Implications for the global tuna fishing industry of climate change-driven alterations in productivity and body sizes

Tunas and billfishes are the main large pelagic commercial fish species. Tunas comprised around 5.5 million t and USD 40 billion in 2018. Climate change studies and projections estimate that overall, global fisheries productivity will decrease due to climate change. However, there are seldom projections of the climate-driven productivity of the higher trophic levels where tunas and billfishes belong. In this work, we use a mechanistic model to evaluate the effects of climate change and fishing for globally distributed and commercially exploited seven tuna species and swordfish which are divided into 30 stocks for management purposes, under a range of climate change (RCP 2.6 and 8.5) and fishing scenarios (from no fishing to 1.5 times the fishing mortality (F) at the Maximum Sustainable Yield, FMSY) from two Earth System Models (IPSL and MEDUSA). The results suggest that high trophic level species will be more impacted by climate change than by fishing pressure under the assumption that they remain nearby their MSY levels. However, no-fishing scenarios project much higher biomass. The overall productivity of the target species will decrease by 36% and only the Pacific bluefin showing a slight increase in the future. Five species; Atlantic and Southern bluefins, swordfish, bigeye, and albacore are estimated to decrease in biomass and size at different rates. These species represent almost a third of the landings in the Atlantic Ocean and 10% in the Pacific Ocean being the bluefins, the highest-valued tuna species. On average, the body size is expected to decrease up to 15% by 2050. Fish price and demand are partially driven by body size and therefore, revenues can be reduced even in stocks with an increase in productivity. The fishing industry can adapt to the changing climate by increasing the value of fish through sustainability certifications and reducing fuel consumption and time at sea with higher digitalization. Reducing fuel consumption would also be an additional mitigation measure to climate change since it would reduce CO2 emissions.