Alec J. Duncan

Bio: Alec J. Duncan is an academic researcher from Curtin University. The author has contributed to research in topics: Underwater acoustic communication & Noise. The author has an hindex of 14, co-authored 99 publications receiving 707 citations. Previous affiliations of Alec J. Duncan include University of Bath.

Localization of individual mulloway (Argyrosomus japonicus) within a spawning aggregation and their behaviour throughout a diel spawning period

Abstract: Mulloway (Argyrosomus japonicus) are a soniferous member of the Sciaenidae. During summer in the Swan River of Western Australia, individuals form spawning aggregations in turbid waters around high tide, during late afternoon and early evening. Mulloway produce pulsed vocalizations that are characteristic of the species and to an extent of individuals. Crepuscular passive acoustic recordings of vocalizing mulloway were collected from a four-hydrophone array during March 2008. Arrival-time differences proved the most robust technique for localization. Corroboration of fish position was observed in relative energy levels of calls, surface-reflected path differences, and relative range of successive calls by individuals. Discrete vocal characteristics of the tone-burst frequency and soundpressure levels assisted the determination of caller identification. Calibration signals were located within a mean distance of 3.4 m. Three-dimensional locations, together with error estimates, were produced for 213 calls during a sample 4-min period in which 495 calls were audible. Examples are given of the movement and related errors for several fish successfully tracked from their vocalizations. Localization confirmed variations in calling rates by individuals, calling altitudes, and the propensity to vary call structure significantly over short periods, hitherto unreported in this species.

A review of current marine mammal detection and classification algorithms for use in automated passive acoustic monitoring

Abstract: The detection and classification of marine mammal vocalisations is an important component in noise mitigation strategies and in the tracking of animals for research purposes. These complex vocalisations span a broad range of frequencies with differences between and within species, and with temporal and geographical variations adding further complexity. Passive Acoustic Monitoring (PAM) systems can be deployed for long periods and can collect large volumes of data, becoming impractical for human operators to manually process due to the significant effort required. Many signal processing algorithms to automate this process have been produced with mixed results. Some are focused on the identification of single species while others handle a variety. No single algorithm is ideal for detecting and classifying all species concurrently, so any automated system requires a suite of these algorithms. A number of these algorithms are summarised here as part of an initial step in the construction of a PAM system incorporating real-time detection and classification.

In situ source levels of mulloway (Argyrosomus japonicus) calls.

Abstract: Mulloway (Argyrosomus japonicus) in Mosman Bay, Western Australia produce three call categories associated with spawning behavior. The determination of call source levels and their contribution to overall recorded sound pressure levels is a significant step towards estimating numbers of calling fish within the detection range of a hydrophone. The source levels and ambient noise also provide significant information on the impacts anthropogenic activity may have on the detection of A. japonicus calls. An array of four hydrophones was deployed to record and locate individual fish from call arrival-time differences. Successive A. japonicus calls produced samples at various ranges between 1 and 100 m from one of the array hydrophones. The three-dimensional localization of calls, together with removal of ambient noise, allowed the determination of source levels for each call category using observed trends in propagation losses and interference. Mean source levels (at 1 m from the hydrophone) of the three call categories were calculated as 163 ± 16 dB re 1 μPa for Category 1 calls (short call of 2–5 pulses); 172 ± 4 dB re 1 μPa for Category 2 calls (long calls of 11–32 pulses); and 157 ± 5 dB re 1 μPa for Category 3 calls (series of successive calls of 1–4 pulses, increasing in call rate).

Analysis of impulsive biological noise due to snapping shrimp as a point process in time

Abstract: Impulsive biological noise produced by snapping shrimp provides an important contribution to the ambient acoustic noise in warm, coastal waters. The challenge is to understand and model the properties of shrimp noise to reduce its impact on sonar and underwater acoustic telemetry systems. Shrimp snaps are impulsive events occurring apparently at random. The short duration of each snap allows these events to be modeled as a point process in time. Point processes are used to model many naturally occurring phenomena including neuron firings, seismic events, radioactive decay, lightning discharges and shot noise in semiconductors. In this paper, point process analysis techniques are applied to real shrimp noise. Inter-snap interval histogram and Fano-factor analysis provide strong evidence that the snaps are not homogeneous Poisson distributed in time. Further analysis based on the rate function suggests that the data may be more appropriately modeled by a doubly stochastic Poisson process.

Estimating animal population density using passive acoustics

Abstract: Reliable estimation of the size or density of wild animal populations is very important for effective wildlife management, conservation and ecology. Currently, the most widely used methods for obtaining such estimates involve either sighting animals from transect lines or some form of capture-recapture on marked or uniquely identifiable individuals. However, many species are difficult to sight, and cannot be easily marked or recaptured. Some of these species produce readily identifiable sounds, providing an opportunity to use passive acoustic data to estimate animal density. In addition, even for species for which other visually based methods are feasible, passive acoustic methods offer the potential for greater detection ranges in some environments (e.g. underwater or in dense forest), and hence potentially better precision. Automated data collection means that surveys can take place at times and in places where it would be too expensive or dangerous to send human observers. Here, we present an overview of animal density estimation using passive acoustic data, a relatively new and fast-developing field. We review the types of data and methodological approaches currently available to researchers and we provide a framework for acoustics-based density estimation, illustrated with examples from real-world case studies. We mention moving sensor platforms (e.g. towed acoustics), but then focus on methods involving sensors at fixed locations, particularly hydrophones to survey marine mammals, as acoustic-based density estimation research to date has been concentrated in this area. Primary among these are methods based on distance sampling and spatially explicit capture-recapture. The methods are also applicable to other aquatic and terrestrial sound-producing taxa. We conclude that, despite being in its infancy, density estimation based on passive acoustic data likely will become an important method for surveying a number of diverse taxa, such as sea mammals, fish, birds, amphibians, and insects, especially in situations where inferences are required over long periods of time. There is considerable work ahead, with several potentially fruitful research areas, including the development of (i) hardware and software for data acquisition, (ii) efficient, calibrated, automated detection and classification systems, and (iii) statistical approaches optimized for this application. Further, survey design will need to be developed, and research is needed on the acoustic behaviour of target species. Fundamental research on vocalization rates and group sizes, and the relation between these and other factors such as season or behaviour state, is critical. Evaluation of the methods under known density scenarios will be important for empirically validating the approaches presented here.

Emerging opportunities and challenges for passive acoustics in ecological assessment and monitoring

Abstract: 1. High-throughput environmental sensing technologies are increasingly central to global monitoring of the ecological impacts of human activities. In particular, the recent boom in passive acoustic sensors has provided efficient, noninvasive, and taxonomically broad means to study wildlife populations and communities, and monitor their responses to environmental change. However, until recently, tech-nological costs and constraints have largely confined research in passive acoustic monitoring (PAM) to a handful of taxonomic groups (e.g., bats, cetaceans, birds), often in relatively small-scale, proof-of-concept studies.2. The arrival of low-cost, open-source sensors is now rapidly expanding access to PAM technologies, making it vital to evaluate where these tools can contribute to broader efforts in ecology and biodiversity research. Here, we synthesise and critically assess the current emerging opportunities and challenges for PAM for ecological assessment and monitoring of both species populations and communities.3. We show that terrestrial and marine PAM applications are advancing rapidly, fa-cilitated by emerging sensor hardware, the application of machine learning inno-vations to automated wildlife call identification, and work towards developing acoustic biodiversity indicators. However, the broader scope of PAM research remains constrained by limited availability of reference sound libraries and open-source audio processing tools, especially for the tropics, and lack of clarity around the accuracy, transferability and limitations of many analytical methods.4. In order to improve possibilities for PAM globally, we emphasise the need for col-laborative work to develop standardised survey and analysis protocols, publicly archived sound libraries, multiyear audio datasets, and a more robust theoretical and analytical framework for monitoring vocalising animal communities.

Shallow-water imaging multibeam sonars: A new tool for investigating seafloor processes in the coastal zone and on the continental shelf

Abstract: Hydrographic quality bathymetry and quantitative acoustic backscatter data are now being acquired in shallow water on a routine basis using high frequency multibeam sonars. The data provided by these systems produce hitherto unobtainable information about geomorphology and seafloor geologic processes in the coastal zone and on the continental shelf. Before one can use the multibeam data for hydrography or quantitative acoustic backscatter studies, however, it is essential to be able to correct for systematic errors in the data. For bathymetric data, artifacts common to deep-water systems (roll, refraction, positioning) need to be corrected. In addition, the potentially far greater effects of tides, heave, vessel lift/squat, antenna motion and internal time delays become of increasing importance in shallower water. Such artifacts now cause greater errors in hydrographic data quality than bottom detection. Many of these artifacts are a result of imperfect motion sensing, however, new methods such as differential GPS hold great potential for resolving such limitations. For backscatter data, while the system response is well characterised, significant post processing is required to remove residual effects of imaging geometry, gain adjustments and water column effects. With the removal of these system artifacts and the establishment of a calibrated test site in intertidal regions (where the seabed may be intimately examined by eye) one can build up a sediment classification scheme for routine regional seafloor identification. When properly processed, high frequency multibeam sonar data can provide a view of seafloor geology and geomorphology at resolutions of as little as a few decimetres. Specific applications include quantitative estimation of sediment transport rates in large-scale sediment waves, volume effects of iceberg scouring, extent and style of seafloor mass-wasting and delineation of structural trends in bedrock. In addition, the imagery potentially provides a means of quantitative classification of seafloor lithology, allowing sedimentologists the ability to examine spatial distributions of seabed sediment type without resorting to subjective estimation or prohibitively expensive bottom-sampling programs. Using Simrad EM100 and EM1000 sonars as an example, this paper illustrates the nature and scale of possible artifacts, the necessary post-processing steps and shows specific applications of these sonars.

The soundscape of the Anthropocene ocean.

Abstract: Oceans have become substantially noisier since the Industrial Revolution. Shipping, resource exploration, and infrastructure development have increased the anthrophony (sounds generated by human activities), whereas the biophony (sounds of biological origin) has been reduced by hunting, fishing, and habitat degradation. Climate change is affecting geophony (abiotic, natural sounds). Existing evidence shows that anthrophony affects marine animals at multiple levels, including their behavior, physiology, and, in extreme cases, survival. This should prompt management actions to deploy existing solutions to reduce noise levels in the ocean, thereby allowing marine animals to reestablish their use of ocean sound as a central ecological trait in a healthy ocean.