Ganges river dolphins may synchronise their activity with time, tides and the moon

In the tidal waters of West Bengal’s Rupnarayan river, Ganges river dolphins live with constantly shifting water levels, currents and conditions. A new study in the river found that tide, time of day and lunar cycle influences when the dolphins were detected. Published in Aquatic Mammals, the month-long study examined the these parameters together in relation to acoustic detections (monitoring the animal by the sounds it makes) of Ganges river dolphins. At the study site, tides rise and fall twice a day with occasional tidal bores, causing large shifts in water levels and the currents, explains Gargi Roy Chowdhury, principal project associate at Wildlife Institute of India (WII) and the first author of the study. “It is a human-modified landscape with intense motorised fishing, and industrialised lower reaches with the Kolaghat thermal power plant downstream of the study site. It holds a good population of dolphins,” she adds while noting that large vessel traffic is limited here. A river shaped by the tide The Rupnarayan is an 85-km-long tributary of the Hooghly, influenced by tides from the Bay of Bengal, about 220 km away. Its upper reaches have narrower channels, while the lower stretches are wider. The river also experiences periodic tidal bores, and its flow is shaped by both seasonal and tidal forces. At the study site, the team used a single F-POD or a full waveform capture pod, an underwater acoustic recorder that listens for dolphin echolocation clicks. “The physical challenge was that the F-POD had to be…This article was originally published on Mongabay