Category Archives: Underwater Acoustics

New Paper: Assessing snubfin dolphin conservation status

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Last month I co-authored a paper on “Regional Assessment of the Conservation Status of Snubfin Dolphins in the Kimberley Region, Western Australia”. Published in Frontiers in Marine Science, this has been a real slow-burn project! The team originally started work on this back in 2013, and since then the project expanded in both breadth and complexity! But it was one of those projects that was just a real delight to work on because of the endearing nature of the animals and the lovely group of people involved.

Snubfin dolphins – or should that be snub-nosed? (Photo: Sarah Marley)

Snubfin dolphins are also locally-known as ‘snub-nosed dolphins’ – and when you look at their wee faces you can see why! They are generally fairly cryptic animals, sitting quite low in the water with relatively small dorsal fin. So easily overlooked if the sea starts to get a bit choppy! They are also a lot less ‘showy’ than some other dolphin species (I’m looking at you bottlenose!), so more likely to quietly disappear than they are to head over to the research vessel and start a cheeky bow-ride. As a result of this and the fact that they exclusively occur in the tropical waters of northern Australia and southern Papua New Guinea (i.e. a very remote location!), scientists still have a lot to learn about their abundance and habitat use. This is a problem when it comes to assessing the conservation status of a species – how do we know if they need help?

This study aimed to address this issue by building the first comprehensive catalogue of snubfin dolphin sightings in the Kimberley, which is thought to be one of their key areas. One of the cool and unique things about this research was that it collated sightings from multiple sources, such as citizen science initiatives, government archives, online repositories, and scientific publications, as well as dedicated research surveys with local Indigenous communities and Ranger groups. This resulted in over 1,500 sightings across a 17-year period. Sightings were mapped to highlight potential hotspots, link detections with particular environmental features, and identify potentially-suitable habitats.

Known and likely distribution of snubfin dolphins across the Kimberley (Source: Bouchet et al. (2021) Supplementary Figure S6).

We found that snunfin dolphins occur in shallow, inshore habitats that are in the vicinity of freshwater outflows. This supports observations by previous researchers. Worryingly, this brings snubfins into close contact with human threats, such as gillnet fisheries, shark control nets, vessel traffic, noise and chemical pollution, and much else.

Finally, we compared these findings with the criteria used by the International Union for the Conservation of Nature (IUCN) for defining whether a species is high priority for conservation. Our results suggest that snubfin dolphins are likely ‘Vulnerable’ at a regional scale – i.e. facing a high risk of extinction in the wild. This emphasises the importance of continuing to monitor these dolphins, as well as demonstrating the value of utilising many different sources of sightings data for a difficult-to-study species.

Apart from the opportunity to work with some dear friends, this project was also important because it actively incorporated the expertise of several Indigenous Ranger groups. Going forwards, these groups will play a crucial role as land managers in local conservation efforts.

New paper: Effects of ship noise on marine mammals

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I’m excited to announce the publication of my co-authored paper on “The Effects of Ship Noise on Marine Mammals—A Review” in Frontiers in Marine Science.

The number of vessels utilising the marine environment is on the rise, with a corresponding increase in noise pollution from this activity. But what are the effects of ship noise on marine mammals? We reviewed 154 scientific articles to document the species, areas, and effects studied. From this, we were able to identify common themes and important research gaps.

This was a hugely satisfying project and a delight to work on. One of the best parts of research is finding great people to work with, which was certainly the case here!

The paper is already receiving good reviews and the Altmetric score is soaring! I’m looking forward to seeing how this paper can help shape future research.

 

 

 

 

Machine Learning and Acoustics

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As computer systems continue to improve, there is an increased ability to complete tasks using artificial intelligence. A computer system can be trained to perceive its environment, make decisions, and take actions. One of the methods for achieving this is machine learning (ML), where machines ‘learn’ tasks from without the need for explicit programming. Given sufficient training, ML can process large, complex datasets to reveal patterns.

abstract blackboard bulb chalk

Photo by Pixabay on Pexels.com

Acoustics is one of the fields generating large amounts of data. For example, every time I deploy a hydrophone in the English Channel, it can record for 3 weeks and return approximately 250 GB of data! It doesn’t take long for the data to quickly add up to an overwhelming amount. Never mind the added challenge of searching through it for sounds of interest, such as fish and vessels. ML could provide the answer, if I could train the computer system to recognise these sounds and search the data for the presence. Similarly, ML could also greatly contribute to other types of acoustic research, like speech processing, sound localisation, noise mitigation, health monitoring, and so on.

But how do young acousticians (yes, I am still counting myself in this category!) learn how to develop and use ML tools? That is where the UK Acoustic Network (UKAN) comes in! The network contains several special interest groups, including one specially devoted to Early Career Researchers that holds an annual Summer School. This year, their aim was to provide training for early career acousticians to get to grips with ML tools. So I joined over 30 scientists at Gregynog Hall in Wales this week for the UKAN Summer School 2019 (#UKANSS19).

The week started with an introduction to Python. This was led by Dr Prasun Ray, a Strategic Teaching Fellow in Applied Mathematics at Imperial College London. Prasun took us through the fundamentals of programming and data analysis in Python, alternating between a mixture of seminars and interactive examples to put us through the paces. Although I haven’t used Python much since 2016, it was good to re-familiarise and get updated on what the software can do!

The ML classes were delivered by Dr Ramon Fuentes (Research Scientist at Callsign Ltd and Visiting Researcher at the University of Sheffield), who has previously applied ML for signal processing and the development of autonomous inspection systems. Although the mathematics of this went whooshing over my biological head, it was still interesting to learn some of the fundamental ideas that ML is built upon. Although anywhere Ramon speaks in the future might want to invest in some additional whiteboards…

Finally, we had a series of lectures on audio and speech applications of ML delivered by Professor Nilesh Madhu from Ghent University. In my opinion, these were the highlight of the week! Nilesh was an excellent speaker, expertly leading us from one topic to another with a strong storyline, a balanced level of detail, plenty of examples, and good humour. His own research focus is on signal detection, analysis and enhancement with application to mobile devices. Despite this seeming fairly different from my own work on the surface, it had a lot of deeper similarities. For example, the problem of recognising and classifying signals in challenging contexts will be particularly relevant to my “Decoding the Deep” project.

As well as generating ideas, the other great thing about this event was meeting people. All too often it is easy to get ‘stuck’ in your own research bubble, only speaking with or working alongside people in the same field. Whilst this can be a good thing, it is still good to step back every so often and look around – because that’s how ideas are born! UKAN exists to support and facilitate networking – and that was a strong highlight of this week. Living with 30+ acousticians for five days means that you never know when an interesting conversation will arise: over the breakfast table; during a lunch break; whilst trying out some casual archery; building a cardboard tower in a competitive team-building exercise; on a hike through the grounds; in a subterranean prison surrounded by the ghosts of past inmates… (not even joking). There were lots of opportunities for networking, bonding, and discussions throughout the week. I think everyone went home with some new contacts and friends, several of which I will be following up with over coming months.

Overall, a successful week for the UKAN Summer School 2019! The ECR Special Interest Group are planning to run another next year, along with some smaller events. Be sure to get in touch to register your interest, propose other events, or join the network!

 

SMM 2017 Conference Presentation

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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.

New Paper: A Tale of Two Soundscapes

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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 of NW Australia

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)

 

New paper: Behavioural and acoustical responses of dolphins to vessel traffic and noise

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Last night, my sixth (and final) PhD paper was published in the journal Scientific Reports!

In earlier papers, I established that the Swan River is a pretty noisy place.  One of the noisiest sites from an anthropogenic perspective is the Fremantle Inner Harbour, which experiences high levels of vessel traffic.  However, during my initial visual observations I discovered that dolphins continued using the harbour, even though it was a busy noisy environment.  So in this latest paper, I searched for evidence of dolphins responding to boats and noise at a subtler scale.

To do this, I used a combination of visual and acoustic monitoring techniques.  I found that dolphins significantly increased their movement speeds when vessel traffic occurred at high levels.  Similarly, dolphins also changed their behavioural budgets at high vessel densities, spending more time travelling and less time resting or socialising.

I monitored dolphin movement speeds and behaviours, to see how these changed as vessel traffic increased

I also looked for acoustic responses, by measuring nine characteristics to describe the shape and frequencies of dolphin whistles in different noise scenarios.  I found that all nine of these characteristics varied with increasing levels of broadband noise, and that the response was particularly strong for low-frequency noise.

I used nine characteristics to describe dolphin whistles

I’ve spoken before about the importance of scientific publishing, in terms of career brownie points for researchers.  So I’m pretty chuffed to have completed publishing my PhD!  To view the full list of papers from this and other projects, check out my Publications page.  Now to deal with all the ‘leftover’ PhD data that I collected, but didn’t get around to including!

New Paper: Spatial and temporal variation in dolphin acoustic habitats

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There is a growing awareness of underwater noise in our oceans and the potential impacts of such noise on marine life, an issue which was the major theme of my PhD thesis.  This is particularly relevant for “acoustically-specialised” species, such as dolphins.  However, before we can start investigating the effects of noise on these animals, we first need to define the soundscape of dolphin habitats and examine patterns of when and where noise occurs.

We get a glimpse of them at the surface – but what about their acoustic habitat beneath the surface? (Photo: Sarah Marley)

This description of noise in dolphin habitats formed my third PhD chapter, which has now been published online in the scientific journal Frontiers in Marine Science.  In this paper, I examine spatial and temporal variability in the soundscape of the Swan River using over 11,600 hours of acoustic data collected from five sites within the river system across eight years.  Multiple sound sources were recorded at these sites, but the prevalence of these sounds at each site differed, giving each location a characteristic soundscape.  Consequently, some sites were ‘noisier’ than others.

Deploying acoustic recording equipment with help from Fremantle Ports. Spot the dolphins in the background! (Photo: Jeanette Murray)

Want to know more?  The full paper is available online! I’d love to hear your thoughts 🙂

Marley et al. (2017) Spatial and temporal variation in the acoustic habitat of bottlenose dolphins (Tursiops aduncus) within a highly urbanised estuary.  Frontiers in Marine Science, 4: 197.

And watch this space, as the remaining three PhD papers should be going up online in the next few months!

 

 

New Video: The Dolphin and the Sound

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As you know, I’m fortunate enough to be sister to the amazing wildlife film-maker Lisa Marley.  I’ve written about her documentary on Scottish raptor poisonings here previously (and incidentally, this work is currently touring the film festivals – scroll to the end for details!).  But in June, we actually worked together on a short film project as part of the Aquatic Noise 2016 conference I attended in Dublin.

The conference held a public evening involving short lectures around the theme of underwater noise, and also invited submission of videos on this topic.  Lisa and I worked together to create a short film describing the effects of human noise on coastal dolphins, similar to the idea of my 3MT speech – but with much cooler visuals than just me standing on a stage!

I wonder if anyone recognises the locations involved in this production?  Suggestions on a postcard please…!

So now I have a professional video to highlight my research AND had the awesome experience of working on a creative project with my sister.  And all without a single sibling squabble to be seen!

“Red Sky on the Black Isle” lastest screenings:

  • Hebrides International Film Festival (on Lewis, Harris, Uist and Barra; UK):  14-17 September 2016
  • Aberdeen Film Festival (UK):  17 October 2016
  • Festival de Menigoute (France):  27 October 2016

Follow the film’s Facebook page for more updates!

New Paper: Fish Choruses in Darwin Harbour

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ICES Journal ArticleAs well as working on my PhD, I’m also lucky enough to be involved in other projects at the Centre for Marine Science and Technology (CMST) from time-to-time.  Now the results from one of these projects have been published in the ICES Journal of Marine Science.

A couple of years ago, I was asked to review acoustic data from Darwin Harbour, in the Northern Territory of Australia.  I’ve written before about the variety of sounds produced by fish, and in the Darwin data we found oodles of different fish choruses.  Fish sounds can be species and size specific, and such en masse sound production often has behavioural associations, for example by corresponding with feeding or reproduction.

So there is a lot of information to be gained by listening in on fish!

In this paper, we recorded nine different types of fish choruses and investigate their patterns of occurrence.  Environmental conditions such as lunar patterns, time of sunset, temperature, tidal information and salinity levels all contributed to the context of when particular choruses were heard.  These results are useful not only to scientists but also to fisheries managers, as it provides improved knowledge regarding species distribution, fish habitat-use, identifies spawning seasons, and monitors behaviour.  Which, when you can’t see fish below the surface, is often difficult data to collect!

The full paper (doi: 10.1093/icesjms/fsw037) is available here.

First PhD Chapter Published!

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After months of graft, I’m extremely chuffed to announce that my first PhD chapter has now been published online!

Chapter 1 - Marley et al 2016

To view the full article, please visit the Springer website.  If you have any issues, please contact me.

One down, one draft on supervisor’s desk, and three more to go!