Category Archives: Soundscapes

SMM 2017 Conference Presentation

I’m now safely home after attending the Society for Marine Mammalogy’s biennial conference in Halifax, Nova Scotia.  It was an amazing eight days of conference talks and workshops, interspersed with plenty of networking.  As well as meeting lots of interesting new people, it was particularly wonderful to catch up with so many old friends.  Totally worth the 35hrs of one-way travel and 12hr time difference jetlag!

I’m currently preparing a detailed conference report for the Journal of Animal Ecology’s blog, but in the meantime I wanted to make my conference presentation available online.  To download a PDF version, click here.  The full abstract is provided below.  Feedback welcome!

SMM 2017 - Sarah Marley

Acoustic habitats and behavioural responses of bottlenose dolphins in Western Australia

Marley, S.A., Salgado Kent, C.P., Erbe, C., Parnum, I.M. and Parsons, M.J.G.

As human activities continue to expand across the marine environment, anthropogenic ocean noise is also rapidly increasing.  This is of concern to acoustically-specialised species, particularly those displaying a high degree of habitat overlap with anthropogenic activities, such as bottlenose dolphins (Tursiops sp.).  There is a need to describe the soundscape of coastal dolphin habitats and examine how prominent anthropogenic noise sources may impact these animals.  The Swan River in Western Australia flows through the state capital of Perth, containing over 1.4 million people, and consequently experiences a range of anthropogenic activities.  However, the river is also extensively used by a resident community of Indo-Pacific bottlenose dolphins (T. aduncus).  Autonomous underwater acoustic recorders were used to collect data throughout the Swan River, which were analysed via weekly spectrograms, power spectrum density percentile plots, octave-band levels, broadband noise levels, and generalised estimating equations.  Land-based theodolite tracking at two sites provided information on vessel traffic and dolphin behaviour, which were assessed using generalised additive models and Markov chains.  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 ‘noisiest’ site from an anthropogenic perspective and in relation to dolphin communications was the Fremantle Inner Harbour (mean broadband noise level: 106 dB re 1 µPa rms [10 Hz – 11 kHz]).  Theodolite tracking at this site found that dolphins remained present during periods of high vessel traffic.  However, behavioural observations indicated significant alterations to dolphin movement speeds and activity states at high vessel densities.  Furthermore, whistle characteristics varied in conditions of high broadband noise.  This work suggests that dolphins maintain occupancy at key foraging sites within the Swan River despite the presence of vessels, but alter their behaviour in periods of high vessel traffic.

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New Paper: A Tale of Two Soundscapes

I am a little bit behind in posting about my various PhD publications.  But a pretty cool one that came out in the August edition of Acoustics Australia focused on comparing the acoustic characteristics of urban versus pristine coastal dolphin habitats.

I’ve previously spoken about the need to define the soundscape of dolphin habitats and examine patterns of when and where noise occurs.  But whilst we can monitor dolphin acoustic habitats and describe how they are now, in many cases it is hard to say how they were in the past.  We simply don’t have enough long-term datasets that capture the expansion of human activities into the marine environments – i.e. datasets that go far enough back in time to capture when the habitat was pristine and free of human influence.  Understandably, this can also make it hard to decide how we best manage man-made noise in these habitats into the future.  It’s hard to determine what noise mitigation measures are necessary when you don’t know how quiet an area is ‘supposed’ to be.

A potential solution to this conundrum for managing ‘urban’ areas is to find comparable ‘pristine’ areas which are also used by the study species, and see what differences exist.  Of course, this is reliant upon pristine areas still existing in the first place.  However, in Western Australia we are fortunate enough to have some areas up in the remote north of the state.

The Kimberley region in north-western Australia is one of the most remote, pristine wildernesses in the world.  The largest town in the region is Broome, which has a permanent population of only 16,000 people (although the temporary population can increase to 45,000 in the tourism season).  Broome is located on the shores of Roebuck Bay, with a relatively large population of snubfin dolphins and is also regularly used by bottlenose dolphins and humpback dolphins.  This area offers a nice contrast with the busy, urban environment of the Swan River, which flows through the Western Australian state capital of Perth.  This river is also used by bottlenose dolphins.  To create successful noise mitigation strategies for coastal dolphins, there is a need to compare ‘quiet’ and ‘noisy’ acoustic habitats.  Roebuck Bay and the Swan River offer the perfect opportunity to do just this.

Prepping the Roebuck Bay acoustic gear

I chose to compare the pristine soundscape of Roebuck Bay with the Swan River’s anthropogenically-noisiest site, the Fremantle Inner Harbour.  I used autonomous underwater acoustic recorders to monitor the soundscape at these sites, and assessed these using a combination of weekly spectrograms, power spectrum density percentile plots and probability densities, octave-band levels, broadband noise levels, and generalised estimating equations – i.e. a shedload of nifty acoustic analyses.

What these essentially showed were that these two sites are very different in their acoustic characteristics.  In Roebuck Bay, biological sounds (such as crustaceans and fish) were the most prevalent sound sources, with very few instances of vessel noise.  However, in the Fremantle Inner Harbour, man-made noise dominated.  This worked out to a 20 dB difference between sites on average, and the frequencies used by dolphins for communication were more likely to be masked in Fremantle Inner Harbour based on elevated noise levels.

In this study, I was also lucky enough to get some acoustic recordings of sounds produced by snubfin and bottlenose dolphins in Roebuck, and could use these for a comparison with the sounds produced by bottlenose dolphins in Fremantle.  This helped me to discuss the potential consequences on Roebuck Bay dolphins if noise levels were to increase at that site.  Such information is going to be useful going into the future, as several coastal developments are currently planned for Roebuck Bay.

To find out more, check the paper out online or contact me!

Snubbies are happy little dolphins – hopefully they stay that way! (Photo: Sarah Marley)