Initial Fisheries Bycatch Estimates for Threatened Marine Mammals in Cambodia

ABSTRACT

Bycatch is the biggest threat to marine mammals globally. To estimate bycatch and investigate bycatch drivers for Irrawaddy dolphin ( Orcaella brevirostris ), Indo‐Pacific humpback dolphin ( Sousa chinensis ), Indo‐Pacific finless porpoise ( Neophocaena phocaenoides ) and dugong ( Dugong dugon ) in Cambodia, questionnaires were conducted with 449 vessels (gillnet, trap, longline, trawl and surrounding net) across Cambodia's coastline between September and October 2023. Collected data included the number of species‐specific bycatch events per vessel, for 1‐ and 5‐year periods. Fishery effort data were obtained from the Cambodian 2018 Fishing Vessel Census. A ratio‐based approach was used to estimate annual bycatch. Bycatch drivers were investigated for Irrawaddy dolphin (only species with sufficient data) by modelling bycatch presence–absence per vessel per 5‐year period as a function of candidate explanatory covariates (e.g., gear and target catch). Bycatch was estimated to 286 Irrawaddy dolphins year ⁻¹ (95% CI 149–464), with gillnets contributing to 66.6% of total bycatch. Gillnets were significantly associated with a higher probability of Irrawaddy dolphin bycatch presence per vessel per 5‐year period (0.18, 95% CI 0.13–0.24) compared to traps (0.03, 95% CI 0.01–0.10). Bycatch was estimated to 60 humpback dolphins year ⁻¹ (95% CI 10–146), 101 finless porpoises year ⁻¹ (95% CI 1–201) and seven dugongs year ⁻¹ (95% CI 0–14), with trawls contributing most to total bycatch for the three species. The results represent the first bycatch estimates for marine mammals in Cambodia and the initial evidence needed to guide further research and conservation action to reduce bycatch.