Jamie Macaulay

Tracking Technologies for Quantifying Marine Mammal Interactions with Tidal Turbines: Pitfalls and Possibilities

Currently, there is great uncertainty surrounding the environmental impacts of tidal turbines on marine mammals; one major concern derives from the potential for physical injury through direct contact with the moving structures of turbines. Collecting data to quantify these risks is challenging and methods for measuring movements underwater and interactions with turbines are limited. However, potential tools include a small number of cutting-edge technologies that are being used increasingly for research and monitoring; these include animal-borne telemetry, and active and passive acoustic tracking. Recent developments in these technologies are described along with their means of application in measuring fine-scale movements and avoidance or evasion responses by marine mammals around turbines. From a risk-characterization perspective, each technique can provide information to inform risk assessments or help parametrize collision risk models; however, each has its associated benefits and drawbacks and it is clear that, in isolation, none of them can provide all the data needed to address the problem. The three approaches appear highly complementary, with the strengths of one complementing the weaknesses in others; the solution to characterizing the risks posed by tidal turbines is likely to be a combination of such techniques.

Passive acoustic methods for fine-scale tracking of harbour porpoises in tidal rapids

The growing interest in generating electrical power from tidal currents using tidal turbine generators raises a number of environmental concerns, including the risk that marine mammals might be injured or killed through collision with rotating turbine blades. To understand this risk, information on how marine mammals use tidal rapid habitats and in particular, their underwater movements and dive behaviour is required. Porpoises, which are the most abundant small cetacean at most European tidal sites, are difficult animals to tag, and the limited size of tidal habitats means that any telemetered animal would be likely to spend only a small proportion of time within them. Here, an alternative approach is explored, whereby passive acoustic monitoring (PAM) is used to obtain fine scale geo-referenced tracks of harbour porpoises in tidal rapid areas. Large aperture hydrophone arrays are required to obtain accurate locations of animals from PAM data and automated algorithms are necessary to process the large quantities of acoustic data collected on such systems during a typical survey. Methods to automate localisation, including a method to match porpoise detections on different hydrophones and separate different vocalising animals, and an assessment of the localisation accuracy of the large aperture hydrophone array are presented.

Acoustic monitoring to document the spatial distribution and hotspots of blast fishing in Tanzania

Destructive fishing using explosives occurs in a number of countries worldwide, negatively impacting coral reefs and fisheries on which millions of people rely. Documenting, quantifying and combating the problem has proved problematic. In March-April 2015 231h of acoustic data were collected over 2692km of systematically laid transects along the entire coast of Tanzania. A total of 318 blasts were confirmed using a combination of manual and supervised semi-autonomous detection. Blasts were detected along the entire coastline, but almost 62% were within 80km of Dar es Salaam, where blast frequency reached almost 10blasts/h. This study is one of the first to use acoustic monitoring to provide a spatial assessment of the intensity of blast fishing. This can be a useful tool that can provide reliable data to define hotspots where the activity is concentrated and determine where enforcement should be focused for maximum impact.

Parameters determining the suitability of bat species for acoustic monitoring

Acoustic monitoring of bats is increasingly used in biodiversity assessments, population monitoring, and environmental impact assessments. In addition to accurate species identification, additional factors make it challenging to derive population trends or better sizes based on acoustic monitoring. Inter- and intra-species- as well as individual variation of acoustic parameters and acoustic activity result in varying detection probabilities. Changes in environmental conditions result in large changes in the volume monitored by the device. Differences in the devices used for acoustic monitoring make it inherently difficult to compare data collected with different devices. The single call monitoring volume is modelled for bats belonging to different guilds under consideration of the different call parameters such as call intensity, frequency, and directionality. By broadcasting bat echolocation calls from various distances to monitoring devices, the acoustic parameters influencing the successful detection of a call were examined. A microphone array was used to track bats in the vicinity of monitoring devices and the distance between device and bat was measured for each call based on the time of arrival difference. The acoustic detection function, the probability of detecting calls as a function of distance, was then derived for multiple detector types.Acoustic monitoring of bats is increasingly used in biodiversity assessments, population monitoring, and environmental impact assessments. In addition to accurate species identification, additional factors make it challenging to derive population trends or better sizes based on acoustic monitoring. Inter- and intra-species- as well as individual variation of acoustic parameters and acoustic activity result in varying detection probabilities. Changes in environmental conditions result in large changes in the volume monitored by the device. Differences in the devices used for acoustic monitoring make it inherently difficult to compare data collected with different devices. The single call monitoring volume is modelled for bats belonging to different guilds under consideration of the different call parameters such as call intensity, frequency, and directionality. By broadcasting bat echolocation calls from various distances to monitoring devices, the acoustic parameters influencing the successful detection o...

Tracking porpoise underwater movements in tidal rapids using drifting hydrophone arrays

The growing interest in generating electrical power from tidal currents using tidal turbine generators raises a number of environmental concerns, including the risk that cetaceans might be injured or killed through collision with rotating turbine blades. To understand this risk we need better information on how cetaceans use tidal rapid habitats and in particular their underwater movements and dive behaviour. Porpoises, which are the most abundant small cetacean at most European tidal sites and we have developed an approach which uses time of arrival differences of narrow band high frequency (NBHF) porpoise clicks at hydrophones in an array drifting in tidal rapids, to accurately track their fine scale movements underwater. Extensive groundtruthing and calibration trials have been carried out that show that the system can provide depth and location data with sub meter errors and also indicate array configurations likely to provide the best balance of accuracy and practicality. Field data from porpoises apparently foraging in strong tidal current areas reveal contrasting behaviours at different locations. A recent surprising observation has been of porpoises diving to ~100m in the Corryvreckan/ Great Race

Arrayvolution—An overview of array systems to study bats and toothed whales

Some echolocation signal parameters can be studied using a single receiver. However, studying parameters such as source level, directionality, and direction of signal emission require the use of multi-receiver arrays. Acoustic localization allows for determination of the position of echolocators at the time of signal emission, and when multiple animals are present, calls can be assigned to individuals based on their location. This combination makes large multi-receiver arrays a powerful tool. Here we present an overview of different array configurations used to study both toothed whales and bats, using a suite of systems ranging from semi-3D-minimum receiver number-number-arrays (3D-MINNAs), linear-2-D-over determined arrays (2D-ODAs), to 3-D-over-determined-arrays (3D-ODAs). We discuss approaches to process and summarize the usually large amounts of data. In some studies, the absolute position of an echolocator and not only relative to the array is crucial. Combining acoustic localizations from a source ...

Determining the detection function of passive acoustic data loggers for porpoises using a large hydrophone array

Click loggers such as C-PODs are an important tool to monitor the spatial distribution and seasonal occurrence of small odontocetes. To determine absolute density, information on the detection function, the detection probability as a function of distance, and derived from this, the effective detection radius (EDR), is needed. In this study a 15 channel hydrophone array, deployed next to 12 C-PODs, was used to localize porpoises and determine their geo-referenced swim paths using the ship’s GPS and motion sensors. The detection function of C-PODs was then computed using the distance between the animals and each C-POD. In addition to this, the acoustic detection function of C-PODs has been measured by playing back porpoise-like clicks using an omni-directional transducer. The EDR for these porpoise-like clicks with a source level of 168 dB re 1 μPa pp varied from 41 to 243 m. This variation seemed to be related to the sensitivity of the devices; however, season and water depth also seemed to have an influen...