Environmental DNA exploring the distribution of Indo-Pacific humpback dolphins and fish diversity from the Pearl River Estuary, China.

Understanding the spatial distribution patterns of endangered species is crucial for their protection. However, gathering such information for cetaceans remains challenging due to their underwater life and elusive nature. Here, by conuding a three-year field ecological survey, we first employed environmental DNA (eDNA) technology to elucidate the distribution and its influencing factors of the Indo-Pacific humpback dolphins from their largest habitat, the Pearl River Estuary (PRE), China. The self-designed SCDloop primers exhibited high specificity for the dolphins and demonstrated elevated eDNA concentrations in proximity to areas with significant human activity in the PRE. Fish species detected in the PRE included most prey items consumed by the dolphins. A significant positive correlation between the occurrence of humpback dolphins and fish diversity was found, indicating the crucial role of fishery resources in the dolphins' habitat selection. Our findings support the use of eDNA technology as a supplementary tool for monitoring marine cetaceans.