Reduced detection of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) in an inner harbour channel during pile driving activities

Abstract

There is limited information on the impacts of anthropogenic noise on dolphin behaviour, making assessment and mitigation of impacts from anthropogenic noises difficult. As the use of echolocation and other vocalizations are of vital importance for cetaceans, it is important to better understand the potential impact of anthropogenic acoustic disturbance. The small Indo-Pacific bottlenose dolphin (Tursiops aduncus) community that inhabits the Fremantle Inner Harbour regularly travels through an area where impact and vibratory pile driving occurred during wharf upgrading. The overall aim of this study was to measure the noise energy created by pile driving associated with wharf construction activities in the Fremantle Inner Harbour and to determine whether the reduced detection of dolphins within the vicinity of the wharf was associated with pile driving activities. Measuring noise was accomplished with noise loggers and a hand-held digital acoustic recorder, under water, allowing identification of signals produced by impact and vibratory pile drivers and calculating the energy of recorded noise. Dolphin detections in the Inner Harbour were conducted by examination of high-definition video recordings. The association of pile driving and dolphin detections was assessed using Generalized Estimation Equations (GEEs), using observations before and during pile driving. The final model indicated that there was a difference in detections between the two treatments, with more dolphin detections observed when there was no pile driving activity taking place (mean = 0.26 ± 0.03 SE) than during pile driving (mean = 0.18 ± 0.04 SE). Knowledge generated by this study on the impact of noise on bottlenose dolphins improves the scientific basis for managing anthropogenic noise and reducing impacts on marine mammals.