On the distribution, behaviour and seasonal variation of Irrawaddy dolphins (Orcaella brevirostris) in the Kep Archipelago, Cambodia

Irrawaddy dolphins (Orcaella brevirostris) are a globally Endangered cetacean species found in rivers, lakes, estuaries, and coastal waters across Southeast Asia. Whilst much attention has concentrated on understanding freshwater populations of the species, marine populations have received less research attention, with the majority of marine studies focusing on determining abundance and distribution. As part of The Cambodian Marine Mammal Conservation Project, the current study utilises a combination of year-long land and boat survey techniques to identify seasonal critical habitats for the species in Cambodia's Kep Archipelago, as well as fill knowledge gaps on the species' behavioural ecology, to contribute to the design of effective and tailored regional conservation strategies. Results showed Irrawaddy dolphins to be present in the Kep Archipelago in all seasons, with the highest encounter rates in Summer Monsoon (May-September) and Post-Monsoon (October-November) seasons, and the lowest encounter rates in Pre-Monsoon season (March-April). Juveniles were present in all seasons, suggesting the region represents an important nursing ground for the population. Foraging was the most commonly observed behaviour, with significant associations found between certain behavioural states and events, group sizes and seasons, group sizes and juvenile presence, and swim styles and juvenile presence.