Vocalization behavior response of captive bottlenose dolphins (Tursiops truncatus) to playbacks of pile driving noise

Abstract

Anthropogenic noises in the ocean may cause significant impacts on the behavior of marine mammals, including stress, hearing impairment, and disruptions in social interactions. To investigate the potential effects of off-shore wind farm pile driving noise on dolphins, we conducted controlled experiments to 3 captive bottlenose dolphins (Tursiops truncatus) exposed to pile driving noise playbacks at four different sound pressure levels (Mean Lpeak 0,127,147,160 dB re 1 μPa) with a Lubell LL1424HP underwater transducer. Several vocalizational parameters of the underwater video recordings during the exposure were analyzed to assess the quantity of vocalizations and frequency modulations. Our findings revealed a notable increase in frequency modulation within whistle calls as the sound levels of pile driving noises increased. Changes in the number of calls at different noise levels can also be noticed. Additionally, we observed time-matching jaw claps to the pile driving sounds. These results suggest that pile driving activity several kilometres away from the habitat may still cause frequency masking, leading to altered behaviors of dolphins and potentially inducing population-level stress. Understanding the impact of anthropogenic noise including behavioral and acoustic responses, auditory masking, and stress on marine species is crucial for effective conservation and mitigation strategies.