Development of a handy mobile 4-hydrophone array system for in-situ census of the Ganges river dolphins (platanista gangetica)

Around 15-20 Ganges river dolphins (platanista gangetica) inhabit the 12-km stretch from Karnavas to Narora Barrage in the Ganges river system. However, more than 10 dolphins were carried away downstream after the flood of June-July 2013. In order to urgently conduct a quick census to secure the dolphins in the original habitat, the existing compact four-hydrophone array system (J-Array) was remodeled for towing, and a function to display the real-time acoustic data on a GUI (Graphical User Interface) on an operational PC at the site was added. Using the new J-Array system, the initial in-situ census in combination with acoustic and visual census was conducted for two days from 19 to 20 November 2013. The functions that were added to the new J-Array performed well. Immediately following the towing survey, using both the acoustic and visual census data, an estimate of the number of the dolphins was made at the site. It was estimated that a minimum of six dolphins were still in the habitat. Off-line acoustic data analysis results were also found in accordance with the in-situ census results. From this, the effectiveness of the new J-Array system for conducting in-situ census has been demonstrated.