Abstract

Cetacean mortality serves as a critical indicator of marine ecosystem health, reflecting the cumulative impacts of climate-driven environmental shifts and anthropogenic pressures. However, long-term national-scale assessments remain limited in Thailand. This study aimed to assess population status, analyse spatiotemporal mortality patterns, and evaluate the influence of environmental drivers and anthropogenic stressors in Thai waters over the past two decades. Secondary data from multiple sources were analysed using generalised linear models with a negative binomial distribution. A total of 29 cetacean species were recorded, with an estimated population of approximately 3000 individuals. Mortality was documented in 24 species and showed an increasing trend over time. Coastal species, particularly Irrawaddy dolphins and finless porpoises, accounted for the majority of deaths (56%). Mortality patterns varied significantly by region (p < 0.05) but not by season, with the highest levels observed in the Upper Gulf of Thailand. Environmental factors were significantly associated (p < 0.05) with mortality, including wind speed in the Andaman Sea and extreme conditions (drought and heavy rainfall) in the Upper Gulf. In the Lower Gulf of Thailand, mortality was significantly associated with a combination of environmental (sea surface temperature and wind speed) and anthropogenic factors (fishery production). Overall, environmental variability appeared to exert a stronger influence than anthropogenic stressors. These findings highlight the requirement for targeted monitoring in high-risk regions and periods, alongside improved investigation of mortality causes to support effective conservation strategies.