Collapse of cetacean biodiversity in the North Yellow Sea: Social media and AIS data uncover anthropogenic threats and conservation hotspots

The North Yellow Sea, once a vital habitat for diverse cetacean populations, has undergone significant ecological decline due to historical whaling, overfishing, and anthropogenic pressures. This study utilizes social media-derived data (2010–2024) and automated identification system (AIS) data from fishing vessels (2021–2024) to assess cetacean biodiversity, spatiotemporal dynamics, cetacean-fisheries interactions, and conservation challenges in this understudied region. Validating 90 records (over 170 individuals) from strandings, bycatch, and opportunistic observations, we documented only seven cetacean species-a stark 50 % decline in species richness compared to pre-1990s records. Spatial analysis revealed 83,385 fishing vessel positions (41.6 % of total) within 10 km of cetacean sightings (mean distance = 5.21 km), with significant hotspot overlap (Pearson's r = 0.185, p < 0.001). The East Asian finless porpoise (Neophocaena asiaeorientalis sunameri) dominated sightings (72.2 % of records), while historically abundant species like the fin whale (Balaenoptera physalus) were absent. Spatial clustering identified critical hotspots in the Changshan Archipelago and Dalian coastal waters, with peak activity in April–May. Fisheries bycatch, evidenced by direct vessel-cetacean co-occurrence (minimum distance = 0.39 km), emerged as the primary threat, while expanding aquaculture infrastructure and chronic vessel noise represent significant secondary pressures. Our findings highlight the urgent need for marine protected areas in identified hotspots, bycatch mitigation strategies (e.g., acoustic deterrents, gear modifications), and enhanced public engagement. This study demonstrates the efficacy of social media as a citizen science tool for monitoring cryptic marine megafauna in data-poor regions, offering actionable insights to reconcile conservation priorities with anthropogenic development.