Spatial and Temporal Variation in the Acoustic Habitat of Bottlenose Dolphins (Tursiops aduncus) within a Highly Urbanized Estuary

Sarah A Marley,Iain M Parnum,Christine Erbe,Miles J G Parsons,Chandra P Salgado Kent

doi:10.3389/fmars.2017.00197

Abstract

There is growing awareness of underwater noise in a variety of marine habitats, and how such noise may adversely aﬀect marine species. This is of particular concern for acoustically-specialised species, such as dolphins. In order to ascertain the potential impacts of anthropogenic noise on these animals, baseline information is required for deﬁning the soundscape of dolphin habitats. The Swan-Canning River system in Western Australia ﬂows through the city of Perth, and experiences numerous anthropogenic activities. Despite this, the river system is home to a community of Indo-Paciﬁc bottlenose dolphins (Tursiops aduncus). To provide a baseline soundscape description of dolphin habitat, over 11,600 h of acoustic data were analysed from ﬁve sites within the Swan River (from Fremantle Inner Harbour to 20 km upstream) across an eight-year period. Multiple sound sources were recorded at these sites, including: snapping shrimp; ﬁshes; dolphins; pile-driving; bridge and road traffic; and vessel traffic. The two most prevalent sound sources, vessel traffic and snapping shrimp, likely have very diﬀerent eﬀects on dolphin communication with the former expected to be more disruptive. Sites were characteristic in their prominent sound sources, showing clear among-site variations, with some sites being ‘noisier’ than others based on broadband noise levels, octave-band noise levels, and power spectrum density percentiles. Perth Waters had the highest broadband noise (10 Hz – 11 kHz; mean 113 dB re 1 µPa rms), whilst Heirisson Island was quietest (mean 105 dB re 1 µPa rms). Generalised estimating equations identiﬁed variation in broadband noise levels within sites at a ﬁne temporal scale, although sites diﬀered in the signiﬁcance of temporal variables. At Mosman Bay, a long-term dataset spanning eight years highlighted inter-annual variation in broadband noise levels, but no overall upwards or downwards trend over time. Acoustic habitats of the Swan River displayed signiﬁcant variations at a variety of temporal and spatial scales, throughout areas frequented by the local dolphin community. Such variations should be quantiﬁed when assessing dolphin acoustic habitat as they may provide signiﬁcant clues to dolphin behaviour.

Highlights

Marine habitats are characterized by a unique combination of topographic structures, environmental conditions, and species compositions
While sounds likely produced by fish occurred at all locations, fish choruses were only observed at the Heirisson Island site (Figure 2C), they are known to occur in other areas of the river such as Blackwall Reach and Mosman Bay (Parsons et al, 2013)
This study describes the acoustic habitat in the core range of the Swan River dolphin community, at varying spatial and temporal scales

Summary

Introduction

Marine habitats are characterized by a unique combination of topographic structures, environmental conditions, and species compositions. These features contribute, either directly or indirectly, to the acoustic conditions of a particular environment as abiotic (e.g., wind, waves, precipitation, ice break-up, earthquakes) and biotic (e.g., crustaceans, fishes, marine mammals) sound sources. Habitats with human activities have the added contribution of anthropogenic sound sources. The “soundscape” of any particular habitat varies in space and time depending on the prevalence of the sound sources within it (Krause, 2008; Pijanowski et al, 2011). For acousticallyspecialized fauna, species occurrence may be influenced by the soundscape of a marine habitat

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