Development and deployment of the long-term in-situ observation system of the Irrawaddy dolphins (Orcaella brevirostris) in Borneo

Abstract

Irrawaddy dolphins are wildly distributed in Asian rivers, lakes and coastal areas. Unfortunately, their population is drastically reducing especially in river areas. Approximately 70-80 Irrawaddy dolphins divided into groups inhabit a 180km stretch of the up-river district of the Mahakam river in Borneo. For understanding the trend of some dolphin groups' migration pattern from Semayang Lake to up/down stream of the river and their echolocation strategy, the stationary observatory using an existing floating house was developed in December 2011 and its first long-term in-situ monitoring was conducted for 3 months in 2012. Taking advantage of the floating house observation platform on the river, one SBL system which consists of a three-piece set of SSBL units with environmental sensors were used for the recording system. In the Mahakam river, boat traffic is steadily increasing. Not only for understanding the trend of the dolphin's migration but also for evaluation of increasing boat noise effect on their echolocation ability, basic acoustic characteristics of the dolphin's echolocation clicks and two typical types of boat noise pulses (type A and type B) were revealed to classify dolphin clicks accurately from boat noise.