Diversity and Distribution of Deep-Sea Cetaceans in the Northern South China Sea Based on Visual and Acoustic Surveys.

Cetaceans are essential for maintaining the balance and stability of deep-sea ecosystems. However, environmental challenges and limited funding have resulted in a marked lack of data on species diversity and the conservation status of deep-sea cetaceans. In this study, we undertook two research expeditions in the deep-water regions of the northern South China Sea, employing an integrated visual and acoustic survey approach. In total, 28 cetacean encounters, involving 12 species and more than 1000 individuals, were documented through visual observation, while acoustic monitoring recorded 53 detections. These findings demonstrate that the deep-sea waters of the northern South China Sea have relatively high cetacean biodiversity and constitute significant habitats for these marine mammals. Nevertheless, this area also experiences intensive human activities, with fisheries, maritime traffic, and oil and gas extraction posing primary threats to local cetacean populations. Improving the management of human activities in this marine zone is essential for ensuring the effective protection of cetacean species and their critical habitats.