Spatio-temporal patterns in underwater sound within an urban estuarine river

Abstract

Underwater noise environments are increasingly being considered in marine spatial planning and habitat quality assessments, particularly with regard to acoustically specialised fauna. The Swan River in Western Australia flows through the state capital of Perth and consequently experiences a range of anthropogenic activities. However, the river is also extensively used by a resident community of bottlenose dolphins (Tursiops aduncus). This study aimed to describe underwater sound sources within the Swan River, examine spatial and temporal soundscape variability, and determine dolphin responses to noisy environments. Acoustic datasets collected from 2005 to 2015 indicated that the Swan River was comprised of multiple acoustic habitats, each with its own characteristic soundscape and temporal patterns in underwater noise. The anthropogenically “noisiest” site was the Fremantle Inner Harbour (mean broadband noise level: 106 dB re 1 μPa rms [10 Hz–11 kHz]); yet dolphins remained present in this area even at high vessel densities. However, fine-scale analyses indicated significant alterations to dolphin behavior at high vessel densities and to dolphin whistle characteristics in high broadband noise conditions. These results highlight the need to consider spatial and temporal patterns when assessing the composition of underwater soundscapes, and identify potential responses of coastal dolphins to busy, noisy environments.Underwater noise environments are increasingly being considered in marine spatial planning and habitat quality assessments, particularly with regard to acoustically specialised fauna. The Swan River in Western Australia flows through the state capital of Perth and consequently experiences a range of anthropogenic activities. However, the river is also extensively used by a resident community of bottlenose dolphins (Tursiops aduncus). This study aimed to describe underwater sound sources within the Swan River, examine spatial and temporal soundscape variability, and determine dolphin responses to noisy environments. Acoustic datasets collected from 2005 to 2015 indicated that the Swan River was comprised of multiple acoustic habitats, each with its own characteristic soundscape and temporal patterns in underwater noise. The anthropogenically “noisiest” site was the Fremantle Inner Harbour (mean broadband noise level: 106 dB re 1 μPa rms [10 Hz–11 kHz]); yet dolphins remained present in this area even at hi...