Climate change and overfishing combine to drive the population decline of the Indo-Pacific humpback dolphins in the Pearl River Estuary from the Northern South China Sea.

Overfishing and climate change pose significant threats to cetacean populations, yet the specific impacts on individual species, particularly cetaceans inhabiting complex coastal areas, are not well understood due to limited data. This study utilizes five years of field survey data, alongside fishery activity and climate change scenarios, to assess the population dynamics of the Indo-Pacific humpback dolphin in the Pearl River Estuary from the Northern South China Sea. Our results indicate a dramatic and ongoing decline in the humpback dolphin population over recent decades, decreasing from over 1000 to 742 individuals. The individual impact of climate change on biomass is moderate, showing changes between -1.3 % and + 11.97 %. Projected climate change scenarios reveal further population reductions, exacerbated by increasing fishing pressures, with declines ranging from 6.17 % to 20.39 %. Notably, our simulations highlight the detrimental effects of unrestrained socioeconomic development on humpback dolphins' viability and population. The dolphins exhibit adaptive dietary strategies to maintain energy levels in changing ecosystems; however, total energy intake still declines across all age classes, requiring increased foraging efforts. This may lead to decreased group sizes, altered distribution patterns, and reduced reproductive success, further increasing their vulnerability to additional stressors. The complex interplay between human activities and environmental changes in marine ecosystems, which significantly impacts cetaceans, provides crucial insights for developing integrated management strategies to safeguard the biodiversity and resilience of coastal marine ecosystems.