Effects of Underwater Noise Levels on the Acoustic Behaviour of Dolphins in the North Channel

Straits provide essential passages connecting marine ecosystems; however, they are areas with very high shipping traffic, increasing levels of anthropogenic noise into the environment which can disrupt essential behaviours for which dolphins are reliant on sound. Although dolphins can adapt the way they communicate, there is vital information that can be lost due to masking of their signals from background noise. Acoustic recordings from two Static Acoustic Monitoring (SAM) devices, including a SoundTrap (Ocean Instruments, NZ) and a SYLENCE-LP (RTsys, France) deployed at two stations in the North Channel were analysed to look at the effects of noise on dolphin whistle behaviour, testing multiple variables: duration, inflection points, whistle shape, and several metrics of frequency (minimum, maximum, delta and peak). These variables were analysed against the Sound Pressure Levels (SPLs) of background noise, using Generalized Linear Models (GLM). Changes in whistle behaviour were expected with increasing noise levels occurring within the dolphins’ hearing range. The change in the whistle parameters depends on the frequency and the SPLs of the ambient noise as it is suggested that dolphins will shift their whistle frequencies to the range that has lower noise interference, to increase the efficiency and detectability of their whistles.