A Matlab Tool For The Characterisation of Recorded Underwater Sound (Chorus)

The advent of low-cost, high-quality underwater sound recording systems has greatly increased the acquisition of large (multi-GB) acoustic datasets that can span from hours to several months in length. The task of scrutinizing such datasets to detect points of interest can be laborious, thus the ability to view large portions of the dataset in a single screen, or apply a level of automation to find or select individual sounds is required. A toolbox that can be continually revised, the user friendly“Characterisation Of Recorded Underwater Sound” (CHORUS) Matlab graphic user interface, was designed for processing such datasets, isolating signals, quantifying calibrated received levels and visually teasing out long and short term variations in the noise spectrum. A function to automatically detect, count and measure particular signals (e.g. blue whale sounds) is integrated in the toolbox, with the ability to include categorised calls of other marine fauna in the future. Sunrise and sunset times can be displayed in long-term average spectrograms of sea noise to reveal diurnal cycles in thevocal activity of marine fauna. A number of example studies are discussed where the toolbox has been used for analysing biological, natural physical and anthropogenic sounds

Quantifying the acoustics packing density of fish schools with a multi-beam sonar

Multi-beam (swath) sonar systems provide the capability to ensonify an entire aggregation of fish in a single pass. However, estimation of abundance and discrimination between species via the use of target strength are considerably more complex than using traditional echosounders, because they ensonify targets at a much wider range of incidence angles. The beam pattern and along beam resolution of multi-beam swaths can produce individual sample volumes that are of similarmagnitude to an individual fish (particularly for large fish, say >1m in length). If individual fish can be resolved, (either as a single fish within a sample, or as multiple contiguous samples that delineate a single fish), and if one assumes that this situation applies to the whole school, acoustic packing density can be determined by dividing the volume of the school by the number of detected acoustic targets. This estimate is proportional to the actual packing density of the fish, defined asthe number of fish per unit volume of water. Acoustic backscatter of fish from a number of schools comprising different species were collected off Perth, in 2005 and 2007, using a Reson Seabat 8125 and 7125 respectively. Nearest neighbour distances of between 1 and 3 body lengths were observed and packing density of acoustic targets showed distinct variation between some species. However, schools of the same species also displayed different acoustic packing densities at differentstages of their growth and development. Such differences were more difficult to observe in schools of fewer fish because the variations in packing density had less impact on the overall volume of the smaller schools associated with fewer fish. Therefore discrimination between species was only deemed possible when surveying two species of different sized fish at the same time. Video ground truth data is recommended to confirm species composition whatever the type of schoolobserved

Source levels of dugong (dugong dugon) vocalizations recorded in Shark Bay

Dugongs (Dugong dugon) spend significant time in shallow, turbid waters and are often active at night, conditions which are not conducive to visual cues. In part, as a result, dugongs vocalize to gain or pass information. Passive acoustic recording is a useful tool for remote detection of vocal marine animals, but its application to dugongs has been little explored compared with other mammals. Aerial surveys, often used to monitor dugong distribution and abundance, are not always financially or logistically viable and involve inherent availability and perception bias considerations. Passive acoustic monitoring is also subject to sampling biases and a first step to identifying these biases and understanding the detection or communication range of animal calls is to determine call source level. In March 2012, four dugongs were fitted with satellite tags in Shark Bay, Western Australia by the Department of Environment and Conservation. During this, acoustic recordings were taken at 5.1 m range. Source levels for each of five call types (two types of chirp, bark, squeak, and quack) were estimated, assuming spherical spreading as the transmission loss. Mean source levels for these call types were 139 (n = 19), 135 (12), 142 (2), 158 (1), and 136 (9) dB re 1 μPa at 1 m, respectively

An investigation into active and passive acoustic techniques to study aggregating fish species

Techniques of single- and multi-beam active acoustics and the passive recording of fish vocalisations were employed to evaluate the benefits and limitations of each technique as a method for assessing and monitoring fish aggregations. Five species, Samson fish (Seriola hippos), mulloway (Argyrosomus japonicus), West Australian dhufish (Glaucosoma hebraicum), Bight redfish (Centroberyx gerrardi) and pink snapper (Pagrus auratus) were investigated on the basis of their abundance, ecological importance and differing behaviour. The primary focus was on S. hippos, a large nonvocal schooling fish, and A. japonicus, a large vocal fish, with each species forming aggregations for spawning purposes.Simrad EQ60 single-beam echosounder assessments of mid-water, S. hippos aggregations at seven sites west of Rottnest Island illustrated the relative biomass increase, stabilisation and decrease between the months of October and March each year from October 2004 to March 2007. Surveys highlighted the preferred sites for spawning, spatial extents of each aggregation, as well as a decline in aggregation stability at full moon and end of season periods. Regular Department of Fisheries surveys displayed the relative ease with which single-beam techniques could be deployed, used and data analysed to monitor large, comparatively stable, deep (>50 m) aggregations of large swimbladdered fish. Acquired acoustic data illustrated the limitations of single-beam surveys conducted on a mobile school of fish.RESON 8125 and 7125 multi-beam sonar (MBS) surveys of S. hippos at Rottnest Island locations, some conducted simultaneously with the Simrad EQ60 single-beam, illustrated the improved spatial resolution of midwater targets achievable with MBS systems. The identification of individual S. hippos targets in MBS data facilitated the confirmation of S. hippos undetected by single-beam transects, due to relative sampling volumes. The MBS surveys showed evidence of possible fishing effects on S. hippos aggregations with school structure varying after a two hour period of fishing and video tows. Relative decline in aggregation stability towards the end of the season and possible avoidance behaviour from approaching vessels was observed as successive MBS transects, over a short space of time, recorded school movement around the wreck above which S. hippos aggregations sit.P. auratus spawning in the Cockburn Sound, Fremantle illustrated the limitations of single-beam acoustics to monitor aggregations of mobile fish in shallow water, due to vessel avoidance behaviour. Similar sampling issues were observed in MBS surveys despite the inherent geometric advantages of the wide acoustic swath and increased sample volume. It was anticipated that adjusting the MBS mounting position, such that nadir beams were orientated laterally athwartships (rather then vertically downwards), increased the lateral distance at which the fish could be observed, thus reducing vessel avoidance implications. However, due to time constraints and equipment availability, remounting the MBS was not possible at the time of survey and the effects of MBS orientation could not be verified.Single-beam and passive acoustic surveys of G. hebraicum illustrated the complexity of acoustic investigation of comparatively sedentary, demersal fish which often spawn in small groups. Discrimination of individuals using single-beam techniques was often restricted by the fish proximity to the seafloor and the footprint of the single-beam. Single-beam species identification of small groups of fish is impractical without simultaneous visual confirmation, due to the stochastic nature of fish reflectance. However, single-beam acoustics could provide information on G. hebraicum spawning related essential fish habitat using seafloor classification. While biological assessment of G. hebraicum otoliths, swimbladder and related muscular structure imply a soniferous species, as yet no vocal behaviour of any of the Glaucosomatidae has been reported, despite attempts here to detect vocalisations. Thus the characteristics of this species presented the greatest limitations for study using active or passive acoustic techniques.Passive acoustic techniques were shown to be ideally suited for monitoring the low density, benthic aggregations of A. japonicus in the Swan River. Spawning related vocalisations of A. japonicus were recorded in situ and in aquaria (Mosman Bay, Swan River and TAFE, Fremantle aquaculture centre respectively) each spawning season between October and May for four spawning seasons. A. japonicus calls, produced by the contraction of bi-lateral paired sonic muscles around the posterior two thirds of a heavily damped swimbladder, were classified into three categories relating to differing spawning functions. Category 1 calls (‘Bup’) of 2-4 swimbladder pulses were believed to function to gather males together in temporary broadcasting territories and to announce readiness to spawn. Category 2 calls comprised 11-32 pulses in a single audible tone (‘Baarp’), which could also be broken into two or more parts (‘Ba-Baarp’) with a believed function as a call of attraction, predominantly from males to females. The third Category comprised calls produced in quick succession at increasing call rate to a point of cessation. Series of Category 3 calls (‘Thup’) were recorded only at times associated with spawning, in fewer numbers than other call categories and consisted of between 1 and 4 pulses.Pulse repetition and spectral peak frequencies of Category 3 calls were notably higher than those of Category 1 and 2, both in situ and in aquaria, despite the similar number of pulses. For example, in situ pulse repetition frequencies of up to 114 Hz for Category 3 calls compared with approximately 59 Hz for other categories. It is suggested that the increased pulse repetition frequencies of Category 3 calls require greater, unsustainable levels of energy (corroborated by the decreasing pulse rate as these calls progress) and such calls are therefore reserved for specific, uncommon events, possibly episodes of courtship. Ground truth in aquaria calls exhibited similar call structure to those recorded in situ, however, pulse repetition rates and occurrence were significantly lower (respective pulse repetition frequencies of 41.74 and 58.68 Hz for captive and in situ Category 2 calls).Season-long monitoring of sound production in Mosman Bay determined spawning commencement was correlated with a daytime water temperature threshold at, or above 18.5 °C, occurring between October and November. Generalized Additive Models showed sound pressure levels (SPLs) and, by proxy spawning throughout the season, were correlated with temperature, salinity, sunset and tidal effects with decreasing order of effect. Increases in short-term sound production were observed on a semi-lunar basis, occurring at the new and full moons. Local chorus level maxima were found to occur on a 3.97 day basis (s.d. = 1.8), similar to that found from egg collection in aquaria and previous in situ SPLs in local studies of A. japonicus. Comparisons between Mosman Bay tidal related afternoon/evening activity and nocturnal behaviour of alternative populations in captivity suggest that A. japonicus exhibits adaptive vocal behaviour, and by proxy spawning activities, dependent on environmental variables.Individual A. japonicus were localised during spawning within and close to an array of hydrophones by using vocalisation arrival-time differences, surface reflection and comparative energy level techniques to analyse vocalisations. Several individual A. japonicus were followed for periods ranging from seconds to several minutes as they called repetitively. Monitoring individual movement and separation distances between calling fish confirmed low mobility over long periods, indicative of lekking behaviour. The determination of call source levels employed calls of known range using data from the localisation study. Mean squared pressure source levels and 95 % confidence limits of the three call categories were measured as: 163 (147.7, 178.6), 172 (168.4, 176.0) and 157 (154.0, 160.3) dB re 1μPa for Categories 1, 2 and 3, respectively.During periods of low density calling in the 2006-7 spawning season, techniques of call counting produced absolute abundance estimates for A. japonicus present within the hydrophone detection range of approximately 500 m, observing a maximum of 15 calling individuals. Assuming a 1.3:1 sex ratio this implies a detectable spawning population of 26 fish within approximately 100, 000 m[superscript]2 (range restricted across stream by depth) equivalent to approximately 3, 850 m[superscript]2 per fish (assuming a random distribution of callers and recipients). However, during high density ‘continuous chorus’ calling the maximum number of callers able to be discerned using call counting techniques was exceeded. The application of call counting techniques and call contributions to overall SPLs to estimate biomass during ‘chorus’ calling, where calls merge together, requires further investigation. Recorded chorus levels were not a simple function of animals calling within the receiver proximity, but were strongly influenced by source-receiver range. A preliminary model to estimate minimum numbers of callers within derived range boundaries has been laid out.Recording of A. japonicus vocalisations illustrated the developing capabilities of passive acoustics to monitor soniferous fish species. A suggested set of protocols has been laid out to standardise the reporting of fish calls together with supplementary data relating environmental variables to their subsequent effects on the acoustic characteristics of the call. Standardisation of reporting will facilitate future spatial and temporal comparison of inter- and intra-species sound production.This study has illustrated that the features of each acoustic technique endear them to particular species-specific characteristics. For example, although S. hippos did not vocalise they formed midwater aggregations of large fish (107 cm mean fork length) and were thus amenable to active acoustic monitoring. In contrast, A. japonicus form low density, benthic aggregations and hence are not suited to study by active acoustics, but vocalised profusely rendering them suitable for passive acoustic monitoring. In many cases a combination of techniques both acoustic and non-acoustic is required to monitor the particular species, in order to ground truth the data

The Spatial Variation of Acoustic Water Column Data and Its Relationship with Reef-Associated Fish Recorded by Baited Remote Underwater Stereo-Videos off the Western Australia Coast

Spatially explicit information on coral fish species abundance and distribution is required for effective management. Nonextractive techniques, including echosounders and video census, can be particularly useful in marine reserves where the use of extractive methods is restricted. This study aimed to investigate the possibility of combining echosounders and baited remote underwater stereo-videos (stereo-BRUVs) in providing more holistic information on the distribution of demersal and semidemersal reef-associated fish. The spatial distribution of fish biomass was assessed using both methods in two small areas, one in Cockburn Sound (CS), a temperate body of water, and the other in the tropical waters of the Ningaloo Marine Park (NMP). The results showed high correlations between the acoustic and stereo-BRUV data in CS, suggesting the potential use of both for a better estimation of biomass in the area. The results for the NMP showed weaker correlations between the two datasets and highlighted the high variability of the system. Further studies are required, but our initial findings suggest a potential benefit of combining both techniques in the reef-associated fish distribution assessment

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

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)

In Situ Calls Of The Marine Perciform Glaucosoma Hebraicum

West Australian dhufish (Glaucosoma hebraicum), a marine perciform, possess a swim bladder which has associated muscles that are used in sound production. Individuals have been recorded producing sounds during capture that may be associated with disturbance from their normal behaviour. To determine whether individuals produce sound during natural behaviour, a passive sea-noise logger was deployed on the seafloor for one month in close proximity to low-relief artificialsubstrates occupied by G. hebraicum. During this time, both juvenile and sub-adult G. hebraicum were observed within metres of the logger on numerous occasions. At approximately the same time, sounds with characteristics similar to the disturbance calls of G. hebraicum were detected by the logger. Two types of swimbladder generated calls were recorded, one of widely-spaced pulses and the other of pulses in quick succession The maximum received levels and sound exposurelevels of the recorded calls were 132 dB re 1 μPa and 121 dB re 1 μPa2.s, respectively. Based on previously determined G. hebraicum source levels and time of arrival techniques (direct and surface-reflected ray paths), the vocalising fish were estimated at between 1 and 19.5 m from the hydrophone and thus within the area where they had been observed. This study has provided evidence that juvenile G. hebraicum produce sounds at similar source levels to those generated during human induced disturbance. This indicates that sound is produced by individuals of this species during normal behaviour, but may or may not be associated with natural sources of disturbance

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

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 sound-pressure 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

Non-song vocalizations of humpback whales in Western Australia

This study presents non-song vocalizations of humpback whales (Megaptera novaeangliae) from two migratory areas off the Western Australian coast: Geographe Bay and Port Hedland. A total of 220 sounds were identified as non-song sounds in 193 h of recordings reviewed. Of those, 68 were measured and qualitatively classified into 17 groups using their spectral features. One group (HW-02) had a high level of variation in terms of spectral slope. However, further classification using statistical classification methods was not possible because of the small sample size. Non-song sound frequencies varied from 9 Hz to 6 kHz, with the majority of sounds under 200 Hz. The duration of non-song sounds varied between 0.09 and 3.59 s. Overall, the use of spectral features allowed general classification of humpback whale sounds in a low sample size scenario that was not conducive to using quantitative methods. However, for highly variable groups, quantitative statistical classification methods (e.g., random forests) are needed to improve classification accuracy. The identification and accurate classification of a species’ acoustic repertoire is key to effectively monitor population status using acoustic techniques and to better understand the vocal behavior of the species. The results of this study improve the monitoring of humpback whales by standardizing the classification of sounds and including them in the species’ repertoire. The inclusion of non-song sounds in passive acoustic monitoring of humpback whales will add females and calves to the detection counts of otherwise only singing males. © Copyright © 2020 Recalde-Salas, Erbe, Salgado Kent and Parsons