Annual behavioral changes of the Ganges river dolphins (Platanista gangetica) based on the three long-term monitoring seasons using 6-hydrophone array system

Abstract

The Ganges river dolphin (Platanista gangetica) belongs to small toothed whale (dolphin) family and inhabits mainly the Ganges river system in India. Like other dolphin species, it uses bio-sonar clicks for echolocation. For understanding the Ganges river dolphin's acoustic behavior over a long-time span, the annual long-term real-time monitoring for 4-6 months in the dry season using 6-hydrophone array system has been conducted for 3 consecutive seasons, i.e. three monitoring phases, since November 2008. 10-14 Ganges river dolphins (adults and calves) that inhabit the 10 km stretch from Karnavas (upstream) to Narora (downstream) in Ganges river system were subjected to the study. In the monitoring, based on the dolphin's high frequency echolocation clicks received on each hydrophone of the array, the system calculates each dolphin's real-time underwater 3-D location around the observation area. It can as well transmit the real-time 3-D location data to the host server by CDMA modem. Any PC with an appropriate viewer program can access the host and monitor the dolphins' real-time movements during the entire monitoring period. Following offline data analysis of each monitoring phase, the underwater behavior of the Ganges river dolphins passing through the observation area is revealed. In addition, based on the off-line data analysis using the three parameters of the click number, average X (longitudinal position along with river) position of the dolphins and its standard deviation (SDX), annual behavioral changes of the Ganges river dolphins for the three monitoring phases is analyzed with consideration of the river configuration changes from season to season.