Acoustic Habitat Research Articles

Impact of maritime security policies on the marine ecosystem

ABSTRACTThe maritime piracy issue drew significant global attention post-2012. The response from the major nations, even those geographically distant from the Indian Ocean Region (IOR), has been highly pro-active. Two important changes that are relevant to this paper are the increased deployment of multi-national naval forces for anti-piracy operations and also re-routing of the shipping lanes closer to the shores. The acoustic impact of these actions was completely ignored but their impact on the marine ecosystem needs to be reviewed. A rare stranding of a blue whale in June 2015 and a Bryde's whale in January 2016, off the west coast of India, are a possible manifestation of the degraded acoustic habitat due to high levels of low-frequency ambient noise in the region. The paper presents an investigative analysis of the two reported events and their correlation with acoustic habitat degradation which may be attributable to increased shipping in the region.

Acoustic habitat of an oceanic archipelago in the Southwestern Atlantic

Underwater soundscapes can be highly variable, and in natural conditions are often dominated by biological signals and physical features of the environment. Few studies, however, focused on oceanic islands soundscapes. Islands in the middle of ocean basins can provide a good example of how untouched marine soundscapes are. Autonomous acoustic recordings were carried out in two different seasons in Trindade-Martin Vaz Archipelago, Southwestern Atlantic, providing nearly continuous data for both periods. Sound levels varied daily and between seasons. During summer, higher frequencies were noisier than lower frequencies, with snapping shrimp being the dominating sound source. During winter, lower frequencies were noisier than higher frequencies due to humpback whale constant singing. Biological signal detection had a marked temporal pattern, playing an important role in the soundscape. Over 1000 humpback whale sounds were detected hourly during winter. Fish vocalizations were detected mostly during night time during both summer and winter. The results show an acoustic habitat dominated by biological sound sources and highlight the importance of the island to humpback whales in winter.

Can you hear me here? Managing acoustic habitat in US waters

Many marine animals have evolved over millions of years to rely on sound as a fun- damental component of their habitat. Over the last century, increasing noise from human activities has significantly affected the quality of underwater acoustic habitats. These changes can lead to reduced ability to detect and interpret environmental cues used to perform critical life functions (e.g. select mates, find food, maintain group structure and relationships, avoid predators, navi- gate). The National Oceanic and Atmospheric Administration (NOAA), as the US federal agency with primary responsibility for protecting marine animals and their habitats, is developing an agency-wide strategy that emphasizes the ocean spaces that these animals need, and the impor- tance of acoustic conditions in those places. This strategy seeks to reach beyond initial goals of reducing acute impacts due to noise (protecting hearing and reducing physical harm) to better account for the importance of underwater sound in marine ecosystems. This paper outlines sci- ence needs associated with acoustic habitat characterization and the assessment of noise impacts on habitats, which provide information critical to NOAA's prioritization of future place-based research and management. NOAA's spatial management tools are examined relative to acoustic habitat protection goals, which seek to match the ecological scales over which noise is impacting marine wildlife, including endangered species. Recommended actions are identified to address these broad spatial and long temporal scales, including international work on quieting technolo- gies, registries of accumulated noisy events, and an enhanced role for NOAA's National Marine Sanctuaries in science, management, and outreach associated with acoustic habitat protection.

Particle motion: the missing link in underwater acoustic ecology

Summary Sound waves in water have both a pressure and a particle‐motion component, yet few studies of underwater acoustic ecology have measured the particle‐motion component of sound. While mammal hearing is based on detection of sound pressure, fish and invertebrates (i.e. most aquatic animals) primarily sense sound using particle motion. Particle motion can be calculated indirectly from sound pressure measurements under certain conditions, but these conditions are rarely met in the shelf‐sea and shallow‐water habitats that most aquatic organisms inhabit. Direct measurements of particle motion have been hampered by the availability of instrumentation and a lack of guidance on data analysis methods. Here, we provide an introduction to the topic of underwater particle motion, including the physics and physiology of particle‐motion reception. We include a simple computer program for users to determine whether they are working in conditions where measurement of particle motion may be relevant. We discuss instruments that can be used to measure particle motion and the types of analysis appropriate for data collected. A supplemental tutorial and template computer code in matlab will allow users to analyse impulsive, continuous and fluctuating sounds from both pressure and particle‐motion recordings. A growing body of research is investigating the role of sound in the functioning of aquatic ecosystems, and the ways in which sound influences animal behaviour, physiology and development. This work has particular urgency for policymakers and environmental managers, who have a responsibility to assess and mitigate the risks posed by rising levels of anthropogenic noise in aquatic ecosystems. As this paper makes clear, because many aquatic animals senses sound using particle motion, this component of the sound field must be addressed if acoustic habitats are to be managed effectively.

Underwater Sound in an Urban Estuarine River: Sound Sources, Soundscape Contribution, and Temporal Variability

Human waterborne activities emit noise into the marine environment. This is of particular concern with regard to the potential impact on marine fauna such as cetaceans due to their acoustic specialisations. The Swan-Canning River system in Western Australia is home to a resident community of Indo-Pacific bottlenose dolphins (Tursiops aduncus), but is also a site regularly used for various human activities. As underwater noise levels increasingly become considered as an indicator of habitat quality, there is a need to characterise the soundscapes of such areas with regard to their cetacean fauna. This study aimed to provide a description of a site within the river system known as “The Narrows”. Acoustic data were collected over a six-week period with an autonomous underwater acoustic recorder. These data were analysed using a combination of weekly spectrograms, power spectral density percentile plots, 1/3 octave band levels, and generalised estimating equations to identify prominent soundscape contributors and investigate temporal patterns in their occurrence. The soundscape was found to be strongly influenced by wind, snapping shrimp, and vessel traffic, with the sounds of bridge traffic, waves, fish, machinery, dolphins, and precipitation also contributing to the acoustic environment. Furthermore, three of these sound sources (boats, waves, and fish) were found to vary at a range of temporal scales. These results take a vital step in characterising the acoustic habitat of this river system, highlighting the need to consider temporal patterns when assessing the composition of underwater soundscapes.

Predicting Anthropogenic Noise Contributions to US Waters.

To increase understanding of the potential effects of chronic underwater noise in US waters, the National Oceanic and Atmospheric Administration (NOAA) organized two working groups in 2011, collectively called "CetSound," to develop tools to map the density and distribution of cetaceans (CetMap) and predict the contribution of human activities to underwater noise (SoundMap). The SoundMap effort utilized data on density, distribution, acoustic signatures of dominant noise sources, and environmental descriptors to map estimated temporal, spatial, and spectral contributions to background noise. These predicted soundscapes are an initial step toward assessing chronic anthropogenic noise impacts on the ocean's varied acoustic habitats and the animals utilizing them.

The relationship between acoustic habitat, hearing and tonal vocalizations in the Antillean manatee (Trichechus manatus manatus, Linnaeus, 1758).

ABSTRACTThe Antillean manatee (Trichechus manatus manatus) is an endangered marine mammal that inhabits the Caribbean Sea and riverine systems in Central America. Their acoustic behavior is relevant for individual identification, mating and parental care. Manatees produce tonal sounds with highest energy in the second harmonic (usually 5 kHz), and their audiogram indicates sensitivity from 0.3 kHz to 90 kHz with lowest thresholds in the 16 to 18 kHz range. We recorded manatees in the San San River, a highly polluted riverine system in Panama, using a stereo array. Frequency transmission experiments were conducted in four subhabitats, categorized using riverine vegetation. Incidental interactions of manatees and small motorboats were examined. Acoustic transmission was linearly related to tonal vocalization characters: correlations were stronger in freshwater than in transition and marine environments. Two bands, 0.6 to 2 kHz and 3 to 8 kHz, attenuate similarly in all subhabitats, and these bands encompass F0 (tone) and peak frequency respectively of manatee tonal calls. Based on our data we conclude that frequency transmission depends mainly on river depth and bottom characteristics, also motorboat sounds mask signals from 3.5 kHz to 8 kHz, which overlaps the peak frequency of tonal calls. In spite of differences between acoustic transmission in subhabitats of the San San River, manatees utilize bands that transmit efficiently in all subhabitats.

Measurement of acoustic material properties of macroalgae (Ecklonia radiata)

Temperate macroalgal forests are among the most productive ecosystems in the world. Acoustic propagation measurements have been used to monitor primary production over broad spatial scales (101–103m) in seagrass meadows, and work is in development to assess the application of acoustics for measuring aggregate production in kelp beds and forests. In addition, scientific echosounders have been used routinely for mapping these benthic habitats and, in some cases, identify dominant species. Further advances in these areas require the development of species-specific acoustic models. However there is little knowledge of the acoustic properties of macroalgae, in part because measuring sound speed in large macroalgae is challenging due to their complex morphology. In this study four different methods are developed and trialled to determine the intrinsic sound speed of Ecklonia radiata tissue based on measurement of the time of flight of an ultrasonic pulse, while compressibility is calculated from density measurements. Direct methods involved lengths of stipe and tightly packed stacks of macroalgae blade tissue. Indirect methods focused on an entire intact macroalga submerged in seawater, and a homogenate solution containing seawater and blended blade tissue. Blade tissue showed a density contrast (relative to seawater) of 1.23 and a sound speed contrast of 1.0374 for the stacks. The homogenate solution gave a sound speed contrast of 1.0424. Stipe tissue density and sound speed were lower. Density contrast was 1.04 and sound speed contrasts were 1.0179 (SD=0.0025) and 1.0064 (SD=0.0032) depending on the sample. Whole macroalgae had age- and size-dependent densities with an average density contrast of 1.11 (SD=0.09) and showed an average sound speed of 1572.8m/s (17.8°C) and contrast of 1.0404 (SD=0.0139). Compressibility was higher in stipe than blade tissue, with 3.924e-10Pa−1 and 3.982e-10Pa−1 for stipes and 3.209e-10Pa−1 and 3.180e-10Pa−1 for blade in stacks and homogenate respectively. The results show that E. radiata sound speed and density are higher, and compressibility lower, than that of seawater. This is likely related to high concentrations of alginate, and other structural and storage carbohydrates in the macroalgae, and thus may vary seasonally. The differences between tissue types found for all properties reflect the morphology and anatomy of this macroalga, with tightly condensed chloroplast cells in blade tissue and loosely packed structural cells in the stipe. This research provides essential input parameters to numerical models that will enhance acoustic habitat mapping and allow the development of acoustic inverse methods. This may enable the estimation of aggregate primary production over large spatial scales in temperate kelp habitats, thus informing their future management.

Temporal and spatial patterns of marine soundscape in a coastal shallow water environment

Underwater acoustic recordings were made at two coastal shallow water locations, Yunlin (YL) and Waishanding (WS), off Taiwan between June and December 2012. The purpose of the study was to establish soundscape baselines and characterize the acoustic habitat of the critically endangered Eastern Taiwan Strait Chinese white dolphin by investigating: (1) major contributing sources that dominant the soundscape, (2) temporal, spatial, and spectral patterns of the soundscape, and (3) correlations of known sources and their potential effects on dolphins. Results show that choruses from croaker fish (family Sciaenidae) were dominant sound sources in the 1.2–2.4 kHz frequency band for both locations at night, and noises from container ships in the 150–300 Hz frequency band define the relative higher broadband sound levels at YL. In addition, extreme temporal variation in the 150–300 Hz frequency band were observed at WS, which was shows to be linked to the tidal cycle and current velocity. Furthermore, croaker choruses are found to be most intense around the time of high tide at night, but not so around the time of low tide. These results illustrate interrelationships among different biotic, abiotic, and anthropogenic environmental elements that shape the unique fine-scale soundscape in a coastal environment.

The effects of road noise on the calling behavior of Pacific chorus frogs

Fitness consequences of anthropogenic noise on organisms that have chorus-dependent breeding requirements, such as frogs, are not well understood. While frogs were thought to have innate and fixed call structure, species-specific vocal plasticity has been observed in populations experiencing high noise conditions. Adjustment to call structure, however, can have negative fitness implications in terms of energy expenditure and female choice. The Pacific chorus frog (Pseudacris regilla), a common vocal species broadly distributed throughout the Pacific Northwest, often breeds in waters impacted by road noise. We compared Pacific chorus frog call structure from breeding populations at 11 high- and low-traffic sites in the Willamette Valley, Oregon. We used passive acoustic monitoring and directional recordings to determine mean dominant frequency, amplitude, and call rate of breeding populations, individual frogs, and to quantify ambient road noise levels. Preliminary results indicate that while individuals do not differ in call rate or structure across noisy and quiet sites, high road noise levels decrease the effective communication distance of both the chorus and the individual. This research enhances our understanding of acoustic habitat in the Willamette Valley and the impacts of anthropogenic noise on a native amphibian species.

Traffic noise causes physiological stress and impairs breeding migration behaviour in frogs.

Human-generated noise has profoundly changed natural soundscapes in aquatic and terrestrial ecosystems, imposing novel pressures on ecological processes. Despite interest in identifying the ecological consequences of these altered soundscapes, little is known about the sublethal impacts on wildlife population health and individual fitness. We present evidence that noise induces a physiological stress response in an amphibian and impairs mate attraction in the natural environment. Traffic noise increased levels of a stress-relevant glucocorticoid hormone (corticosterone) in female wood frogs (Lithobates sylvaticus) and impaired female travel towards a male breeding chorus in the field, providing insight into the sublethal consequences of acoustic habitat loss. Given that prolonged elevated levels of corticosterone can have deleterious consequences on survival and reproduction and that impaired mate attraction can impact population persistence, our results suggest a novel pathway by which human activities may be imposing population-level impacts on globally declining amphibians.

Soundscapes and vocal behavior of humpback whales in Massachusetts Bay

In recent years, technological advances have revolutionized the study of acoustic communication in marine mammals. Exciting new perspectives on vocal behavior, acoustic habitats, and the influence of noise on communication are offered by passive acoustic monitoring (PAM) platforms such as acoustic tags (DTAGs), autonomous PAM recorders, drifting PAM buoys, and subsea gliders. These innovations bring the opportunity to integrate data from fixed and mobile PAM devices to gain deeper insight into the dynamic interactions between marine mammal vocalizations, behavioral context, and the acoustic environment. In this study, we bring together such data sources to study the vocal behavior and acoustic habitat of humpback whales in the context of their spring and summer feeding grounds. Recordings were made in Stellwagen Bank National Marine Sanctuary during 2008–2010, using arrays of autonomous PAM recorders and DTAGs. In addition, AIS ship-tracking data were obtained to study the influence of vessel movements. We present preliminary findings of this work and discuss future strategies for analyzing the spatiotemporal interactions between vocal behavior and acoustical context.

Spectral probability density as a tool for marine ambient noise analysis

The empirical probability density of the power spectral density has been successfully applied as tool to assess signal variability and sensor system performance in the seismic literature. This paper presents the application of this analysis method to underwater ambient noise measurements, and demonstrates its utility in assessing the field performance of passive acoustic monitoring systems and the statistical distribution of noise levels across the frequency spectrum. Using example datasets from an autonomous passive acoustic recorder in the Moray Firth, Scotland, UK, and a cabled subsea observatory in the Strait of Georgia, British Columbia, we show how this method can reveal data limitations such as persistent tonal components and insufficient dynamic range, and phenomena such as bimodality and outliers, which may be undetected by standard analysis techniques. We then combine this approach with conventional percentiles and spectral averages, illustrating how the underlying noise level distributions influence these metrics, and propose this technique as a standard, integrative presentation of ambient noise spectra. Finally, the paper presents cumulative probability density as a method for frequency-domain characterization of chronic noise exposure in marine acoustic habitats.

A New Framework for Assessing the Effects of Anthropogenic Sound on Marine Mammals in a Rapidly Changing Arctic

The recent loss of Arctic sea ice provides humans unprecedented access to the region. Marine mammals rely on sound as a primary sensory modality, and the noise associated with increasing human activities offshore can interfere with vital life functions. Many coastal communities rely on marine mammals for food and cultural identity, and subsistence hunters have expressed strong concerns that underwater sound from human activities negatively affects both the animals and hunting success. Federal regulations require scientists and oil and gas operators to acquire incidental harassment authorizations for activities that may disturb marine mammals. Currently, authorization requests are focused on the impacts of sound from activities considered in isolation of one another, and this precludes any possibility of a meaningful analysis of the cumulative impacts from multiple sources. We propose a new assessment framework that is based on the acoustic habitats that constitute the aggregate sound field from multiple sources, compiled at spatial and temporal scales consistent with the ecology of Arctic marine mammals.

A threatened beluga (Delphinapterus leucas) population in the traffic lane: Vessel-generated noise characteristics of the Saguenay-St. Lawrence Marine Park, Canada

The threatened resident beluga population of the St. Lawrence Estuary shares the Saguenay-St. Lawrence Marine Park with significant anthropogenic noise sources, including marine commercial traffic and a well-established, vessel-based whale-watching industry. Frequency-dependent (FD) weighting was used to approximate beluga hearing sensitivity to determine how noise exposure varied in time and space at six sites of high beluga summer residency. The relative contribution of each source to acoustic habitat degradation was estimated by measuring noise levels throughout the summer and noise signatures of typical vessel classes with respect to traffic volume and sound propagation characteristics. Rigid-hulled inflatable boats were the dominant noise source with respect to estimated beluga hearing sensitivity in the studied habitats due to their high occurrence and proximity, high correlation with site-specific FD-weighted sound levels, and the dominance of mid-frequencies (0.3-23 kHz) in their noise signatures. Median C-weighted sound pressure level (SPL(RMS)) had a range of 19 dB re 1 μPa between the noisiest and quietest sites. Broadband SPL(RMS) exceeded 120 dB re 1 μPa 8-32% of the time depending on the site. Impacts of these noise levels on St. Lawrence beluga will depend on exposure recurrence and individual responsiveness.

Marine acoustic ecologies and acoustic habitats: Concepts, metrics, and realities

Whales, dolphins, and porpoises (cetaceans) are adapted to produce and perceive sounds that collectively span 4–6 orders of magnitude along space, time, and frequency dimensions. Two important concepts, acoustic ecology and acoustic habitat, emerge from this perspective: where acoustic ecology is the study of acoustics involved in interactions of living organisms, and acoustic habitat as ecological space acoustically utilized by particular species. Cetaceans are dependent on access to their normal acoustic habitats for basic life functions. Communication masking from anthropogenic sounds that are chronically present can result in measurable losses of cetacean acoustic habitats, especially for low-frequency specialists, baleen whales. A communication masking model, informed by multi-year datasets, demonstrates cumulative influences of multiple vessels on fin, humpback and right whale acoustic habitats at spatial, temporal, and spectral scales matched to ecologically meaningful habitats. Results quantify acoustic habitat spatio-temporal variability over ecologically meaningful scales. In some habitats with high vessel traffic and vessel noise, predicted habitat loss and area over which animals can communicate is dramatically reduced compared to what it would be under non-vessel conditions. From a large-scale, ecological perspective, these acoustic habitat reductions likely represent significant costs for species for which acoustic communication is biologically critical.

Comparing marine mammal acoustic habitats in Atlantic and Pacific sectors of the High Arctic: year-long records from Fram Strait and the Chukchi Plateau

During the International Polar Year (IPY), acoustic recorders were deployed on oceanographic moorings in Fram Strait and on the Chukchi Plateau, representing the first coordinated year-round sampling of underwater acoustic habitats at two sites in the High Arctic. Examination of species-specific marine mammal calls recorded from autumn 2008–2009 revealed distinctly different acoustic habitats at each site. Overall, the Fram Strait site was acoustically complex compared with the Chukchi Plateau site. In Fram Strait, calls from bowhead whales (Balaena mysticetus) and a variety of toothed whales (odontocetes) were recorded year-round, as were airgun pulses from seismic surveys. In addition, calls from blue whales (Balaenoptera musculus) and fin whales (B. physalus) were recorded from June to October and August to March, respectively. Conversely, at the Chukchi Plateau site, beluga (Delphinapterus leucas) and bowhead whale calls were recorded primarily from May to August, with airgun signals detected only in September–October. Ribbon seal (Phoca fasciata) calls were detected in October–November, with no marine mammals calls at all recorded from December to February. Of note, ice-adapted bearded seals (Erignathus barbatus) were recorded at both sites, primarily in spring and summer, corresponding with the mating season for that species. Differences in acoustic habitats between the two sites were related to contrasts in sea ice cover, temperature, patterns of ocean circulation and contributions from anthropogenic noise sources. These data provide a provisional baseline for the comparison of underwater acoustic habitats between Pacific and Atlantic sectors of the High Arctic.

Acoustic masking in marine ecosystems: intuitions, analysis, and implication

Acoustic masking from anthropogenic noise is increasingly being considered as a threat to marine mammals, particularly low-frequency specialists such as baleen whales. Low-frequency ocean noise has increased in recent decades, often in habitats with seasonally resident populations of marine mammals, raising concerns that noise chronically influences life histories of individuals and populations. In contrast to physical harm from intense anthropogenic sources, which can have acute impacts on individuals, masking from chronic noise sources has been difficult to quantify at individ- ual or population levels, and resulting effects have been even more difficult to assess. This paper pre- sents an analytical paradigm to quantify changes in an animal's acoustic communication space as a result of spatial, spectral, and temporal changes in background noise, providing a functional defini- tion of communication masking for free-ranging animals and a metric to quantify the potential for communication masking. We use the sonar equation, a combination of modeling and analytical tech- niques, and measurements from empirical data to calculate time-varying spatial maps of potential communication space for singing fin (Balaenoptera physalus), singing humpback (Megoptera novaeangliae), and calling right (Eubalaena glacialis) whales. These illustrate how the measured loss of communication space as a result of differing levels of noise is converted into a time-varying mea- sure of communication masking. The proposed paradigm and mechanisms for measuring levels of communication masking can be applied to different species, contexts, acoustic habitats and ocean noise scenes to estimate the potential impacts of masking at the individual and population levels.

Acoustic habitat and shellfish mapping and monitoring in shallow coastal water – Sidescan sonar experiences in The Netherlands

Sidescan sonar has been applied in a number of shallow water environments along the Dutch coast to map and monitor shellfish and seabed habitats. The littoral setting of these surveys may hamper data acquisition flying the towfish in zones of turbulence and waves, but also offers valuable opportunities for understanding, interpreting and validating sidescan sonar images because of the ability to ground-truth during low water periods, enabling easy identification and validation. Acoustical images of some of the mussel banks on the tidal flats of the Wadden Sea, recorded at high tide, show a marked resemblance with optical Google Earth images of the same banks. These sonar images may thus serve as ‘ acoustic type signatures’ for the interpretation of sonar patterns recorded in deeper water where ground-truthing is more difficult and more expensive. Similarly, acoustic type signatures of (Japanese) oyster banks were obtained in the estuaries in the southwest of the Netherlands. Automated acoustic pattern recognition of different habitats and acoustical estimation of faunal cover and density are possible applications of sidescan sonar. Both require that the backscattering observed on the sidescan sonar images is directly caused by the biological component of the seafloor. Filtering offers a simple and effective pre-processing technique to separate the faunal signals from linear trends such as emanating from wave ripples or the central tracks of the towfish. Acoustically estimating the faunal density is approached by in-situ counting peaks in backscattering in unit squares. These counts must be calibrated by ground-truthing. Ground-truthing on littoral mussel banks in the Wadden Sea has been carried out by measuring their cover along lines during low tide. Due to its capacity of yielding full-cover, high resolution images of large surfaces, sidescan sonar proves to be an excellent, cost-effective tool for quantitative time-lapse monitoring of habitats.

Autonomous seafloor recorders and autodetection buoys to monitor whale activity for long-term and near-real-time applications.

Biologists and engineers from Cornell have installed arrays of autonomous seafloor recorders in multiple ocean habitats. These systems are designed to continuously monitor for the occurrence of endangered whales, particularly right whales; provide critical data on whale seasonal occurrence, distribution and relative numbers; and evaluate potential noise impacts from manmade activities and commercial shipping. Recent studies have been conducted in Massachusetts Bay around commercial LNG ports, the Arctic Ocean at seismic study locations, and in New York waters extending to the shelf edge. In combination with Cornell-developed MATLAB- and JAVA-based software applications, these seafloor recorders have been utilized to evaluate seasonal whale presence, calculate levels of commercial shipping and construction noise, and locate and track the movements and behaviors of individual whales under different acoustic conditions. Cornell and ocean engineers from the Woods Hole Oceanographic Institution have installed an operational network of autodetection buoys off New England to provide near-real-time data on right whale presence to transiting LNG vessels, government agencies, and public entities. When combined, the seafloor and autodetection buoy systems provide a powerful mechanism for understanding whale behavioral ecology and describing their acoustic habitats, while mitigating the risks from ship strike and noise exposure.