Long duration real-time acoustic monitoring of Irrawaddy dolphins (Orcaella brevirostris) in Mahakam river in Borneo

Targeting some Irrawaddy dolphin groups that frequently migrate from Lake Semayang to up/down-stream of the river through the tributary and the confluence in the middle-river district of the Mahakam river in Borneo, the long duration real-time acoustic monitoring using a PAM (Passive Acoustic Monitoring) system using arrays of hydrophones at the stationary observatory has been conducted since 2011. After the second monitoring phase was terminated due to lightning damage in October 2013, the recording system was trimmed down to a three-hydrophone array system that can measure the direction of the sound source to monitor the dolphins´ migration behavior in a long-term span. To answer the questions such as: How often and when do they migrate from Lake Semayang to up/down-stream of the river through the tributary, the statistical data analysis using the dolphins´ direction data recorded from the first and second monitoring phases and uploaded to the database was initially carried out for understanding their diel/daily/monthly/seasonal migration trends. The results confirmed that the statistical analysis using the data acquired by the long duration acoustic monitoring could reveal the answers to the above questions: “how often and when”. Answering the further question: “What is the main factor in their migration changes?”- is the next step of the study.