Projected impacts of climate change on the spatial distribution and habitat preference of tropical tuna in the Pacific Ocean

Abstract

Climate change is altering ocean conditions such as sea surface temperature, salinity, stratification, and dissolved oxygen, reshaping habitat suitability for yellowfin tuna (Thunnus albacares, YFT) and bigeye tuna (Thunnus obesus, BET). This study integrated Taiwanese longline catch-per-unit-effort (CPUE) data from 1981 to 2014 with environmental covariates using a Vector Autoregressive Spatio-Temporal (VAST) framework to develop Habitat Suitability Index (HSI) models. Fishing effort increased from similar to 200,000 hooks in 1991 to nearly 820,000 in 2002, before declining to similar to 400,000 by 2021. YFT dominated catches until 2000, after which BET became predominant. Spatial analyses indicated BET hotspots in the tropical central and eastern Pacific, whereas YFT were more abundant in the western Pacific with smaller hotspots in the east. Suitability curves showed BET favored cooler, moderately saline, oxygen-rich waters, while YFT preferred warmer, saltier, and slightly less oxygenated conditions. Coupling HSI models with CMIP6 projections under SSP1-2.6 and SSP5-8.5 revealed contrasting redistribution patterns: BET habitats are projected to contract and shift eastward by the end of the century, while YFT habitats are expected to expand across wider Pacific regions. These findings demonstrate that climate-driven changes in tuna distribution will likely reshape fishery productivity and management requirements. Regionspecific quota adjustments, flexible management zones, and strengthened multinational cooperation will be necessary. Incorporating the HSI outputs into quota setting and spatial planning can help sustain Taiwan's distant-water tuna fisheries in a changing climate.