Automatic detection of echolocation clicks based on a Gabor model of their waveform

Prior research has shown that echolocation clicks of several species of terrestrial and marine fauna can be modelled as Gabor-like functions. Here, a system is proposed for the automatic detection of a variety of such signals. By means of mathematical formulation, it is shown that the output of the Teager–Kaiser Energy Operator (TKEO) applied to Gabor-like signals can be approximated by a Gaussian function. Based on the inferences, a detection algorithm involving the post-processing of the TKEO outputs is presented. The ratio of the outputs of two moving-average filters, a Gaussian and a rectangular filter, is shown to be an effective detection parameter. Detector performance is assessed using synthetic and real (taken from MobySound database) recordings. The detection method is shown to work readily with a variety of echolocation clicks and in various recording scenarios. The system exhibits low computational complexity and operates several times faster than real-time. Performance comparisons are made to other publicly available detectors including PAMGUARD

Issues associated with sound exposure experiments in tanks

For practical reasons it is often necessary to carry out sound exposure experiments on marine animals in tanks or pools that may have dimensions ranging from less than one meter to a few tens of meters. The boundaries of such tanks are almost invariably highly reflective to underwater sound, resulting in a sound field that can vary spatially in unexpected ways, and in which the relationship between pressure and particle velocity is quite different from that in an animal's natural environment. In this paper a numerical simulation based on the finite difference method is used to illustrate these effects. The results show that, at frequencies below the tank's lowest resonant frequency, the particle velocity and pressure fields vary smoothly in space and with changes in frequency, but that both the ratio of the particle velocity to the pressure and the way in which their amplitudes vary with distance from the source are different than in a freefield situation. At frequencies above the lowest resonant frequency the particle velocity and pressure fields, and their ratio, vary rapidly both spatially and with changes in frequency. Experimental measurements of pressure and particle velocity in a tank agree qualitatively with these results. © 2016 Acoustical Society of America

Effect on ocean noise: Nyepi, a balinese day of silence

No Abstract Availabl

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

Matching signature whistles with photo-identification of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the Fremantle Inner Harbour, Western Australia

The Swan–Canning River System is home to an Indo-Pacific bottlenose dolphin (Tursiops aduncus) community of currently 17 adult and juvenile individuals. While a complete photo-identification catalogue exists, visual monitoring requires repeated boat-based surveys and is thus laborious and expensive. Bottlenose dolphins are known to emit individually distinctive signature whistles, and therefore, passive acoustic monitoring could be a reliable and more efficient tool. Archived acoustic and photographic data from the Fremantle Inner Harbour were reviewed for instances when dolphin whistles and individual identifying images were simultaneously available. As dolphin whistles are commonly used in social encounters, dolphins producing whistles in this study were always in groups. Consequently, to assess whether distinctive whistles could be attributed to individual dolphins, conditional probabilities for recording a specific whistle in the presence of certain individuals, as well as Bayesian posterior probabilities for encountering a specific individual at times of certain whistles were computed. While a larger sample size is needed to capture all individuals in diverse groupings, this study provides the first step in developing a passive acoustic program for monitoring this small dolphin community, in order to ultimately inform its conservation management. © 2020, Australian Acoustical Society

Killer whale (Orcinus orca) predation on beaked whales (Mesoplodon spp.) in the Bremer Sub-Basin, Western Australia

Observations of killer whales (Orcinus orca) feeding on the remains of beaked whales have been previously documented; however, to date, there has been no published account of killer whales actively preying upon beaked whales. This article describes the first field observations of killer whales interacting with, hunting and preying upon beaked whales (Mesoplodon spp.) on four separate occasions during 2014, 2015 and 2016 in the Bremer Sub-Basin, off the south coast of Western Australia

Seasonal productivity drives aggregations of killer whales and other cetaceans over submarine canyons of the Bremer Sub-Basin, south-western Australia

Cetaceans are iconic predators that serve as important indicators of marine ecosystem health. The Bremer Sub-Basin, south-western Australia, supports a diverse cetacean community including the largest documented aggregation of killer whales (Orcinus orca) in Australian waters. Knowledge of cetacean distributions is critical for managing the area’s thriving ecotourism industry, yet is largely sporadic. Here we combined aerial with opportunistic ship-borne surveys during 2015–2017 to describe the occurrence of multiple cetacean species on a regional scale. We used generalised estimating equations to model variation in killer whale relative density as a function of both static and dynamic covariates, including seabed depth, slope, and chlorophyll a concentration, while accounting for autocorrelation. Encountered cetacean groups included: killer (n ¼ 177), sperm (n ¼ 69), long-finned pilot (n ¼ 29), false killer (n ¼ 2), and straptoothed beaked (n ¼ 1) whales, as well as bottlenose (n ¼ 12) and common (n ¼ 5) dolphins. Killer whale numbers peaked in areas of low temperatures and high primary productivity, likely due to seasonal upwelling of nutrient-rich waters supporting high prey biomass. The best predictive model highlighted potential killer whale ‘hotspots’ in the Henry, Hood, Pallinup and Bremer Canyons. This study demonstrates the value of abundance data from platforms of opportunity for marine planning and wildlife management in the open ocean

Underwater sound of rigid-hulled inflatable boats

Underwater sound of rigid-hulled inflatable boats was recorded 142 times in total, over 3 sites: 2 in southern British Columbia, Canada, and 1 off Western Australia. Underwater sound peaked between 70 and 400 Hz, exhibiting strong tones in this frequency range related to engine and propeller rotation. Sound propagation models were applied to compute monopole source levels, with the source assumed 1m below the sea surface. Broadband source levels (10–48 000Hz) increased from 134 to 171 dB re 1μPa @ 1m with speed from 3 to 16m/s (10–56 km/h). Source power spectral density percentile levels and 1/3 octave band levels are given for use in predictive modeling of underwater sound of these boats as part of environmental impact assessments

The marine soundscape of the Perth Canyon

The Perth Canyon is a submarine canyon off Rottnest Island in Western Australia. It is rich in biodiversity in general, and important as a feeding and resting ground for great whales on migration. Australia's Integrated Marine Observing System (IMOS) has moorings in the Perth Canyon monitoring its acoustical, physical and biological oceanography. Data from these moorings, as well as weather data from a near-by Bureau of Meteorology weather station on Rottnest Island and ship traffic data from the Australian Maritime Safety Authority were correlated to characterise and quantify the marine soundscape between 5 and 3000. Hz, consisting of its geophony, biophony and anthrophony. Overall, biological sources are a strong contributor to the soundscape at the IMOS site, with whales dominating seasonally at low (15-100. Hz) and mid frequencies (200-400. Hz), and fish or invertebrate choruses dominating at high frequencies (1800-2500. Hz) at night time throughout the year. Ships contribute significantly to the 8-100. Hz band at all times of the day, all year round, albeit for a few hours at a time only. Wind-dependent noise is significant at 200-3000. Hz; winter rains are audible underwater at 2000-3000. Hz. We discuss how passive acoustic data can be used as a proxy for ocean weather. Passive acoustics is an efficient way of monitoring animal visitation times and relative densities, and potential anthropogenic influences