Assessing sound exposure from shipping in coastal waters using a single hydrophone and Automatic Identification System (AIS) data

Unseen overlap between fishing vessels and top predators in the northeast Pacific

Accurate assessments of human-wildlife risk associated with industrial fishing are critical for the conservation of marine top predators. Automatic Identification System (AIS) data provide a means of mapping fishing and estimating human-wildlife risk; however, risk can be obscured by gaps in the AIS record due to technical issues and intentional disabling. We assessed the extent to which unseen fishing vessel activity due to AIS gaps obscured estimates of overlap between fishing vessel activity and 14 marine predators including sharks, tunas, mammals, seabirds, and critically endangered leatherback turtles. Among vessels equipped with AIS in the northeast Pacific, up to 24% of total predator overlap with fishing vessel activity was unseen, and up to 36% was unseen for some individual species. Waters near 10°N had high unseen overlap with sharks yet low reported shark catch, revealing potential discrepancies in self-reported datasets. Accounting for unseen fishing vessel activity illuminates hidden human-wildlife risk, demonstrating challenges and solutions for transparent and sustainable marine fisheries.

Daytime boat sound does not affect the behavior of wild thorny oysters (Spondylus americanus): A field-based study

There is increasing awareness of boat sound effects on coral reef assemblages. While behavioral disturbances have been found in fishes, the effects on marine invertebrates remain largely unknown. Here, the behavioral effects of recreational boat sound on thorny oysters at two coral reef habitats within the U.S. Virgin Island National Park were assessed. The "treatment" site was characterized by frequent boat traffic, which increased daytime mean particle acceleration levels (PALrms) by more than 6 dB, while mean PALrms at the "control" site were not contaminated by boat sound. Despite these contrasting soundscapes, all oysters showed the same diurnal cycle, with their valves open at night and partially closed during the day. There was no statistical evidence of behavioral responses in oysters exposed to daytime boat sound. This can be explained by low auditory sensitivity, habituation to a noisy environment due to the pervasiveness of boat sound pollution, or that boat sound may not represent an immediate concern for this species. These findings contrast with laboratory studies that have shown behavioral responses in bivalves exposed to boat sound, highlighting the need for more realistic field-based studies when evaluating potential effects of anthropogenic sounds on this group.

Analysis of the Underwater Radiated Noise Generated by Hull Vibrations of the Ships

Shipping traffic is recognised as the main man-noise source of the anthropogenic noise generated in the marine environment. The underwater acoustic pollution is increased due to the increment of the human activity at seas supposing a threat for marine habitats. The ship as acoustic source must be understood and controlled to manage the maritime areas both in time and space to reduce the impact of noise in marine fauna. Shipping noise is mainly composed of flow noise, propeller noise and machinery noise. This research is focused on the analysis and estimation of the underwater radiated noise generated by the vibrations of the onboard machinery or structure-borne noise based on the calculation of the transfer function. This function relates the acceleration levels of the vibrations of the hull's panels and the radiated noise by them using the radiation efficiency. Different analytical methods to estimate the radiation efficiency are presented and compared with data collected at sea. The measurements are performed acquiring simultaneously acceleration and acoustic levels by means on accelerometers installed on the hull's panels at different positions and hydrophones deployed close to the bow, middle and stern of the ship. The analysis of the transmission of the vibrations along the ships is performed using the data from different locations of the hydrophones. The quality of the measurements is analysed using the coherence function through the spectral correlation between the measurement of vibrations and acoustic levels. On the other hand, signal-to-noise ratio is computed to verify the strength of the noise sources. The computed transfer function is used to predict the underwater radiated noise from vibrations showing differences less than 2 dB re to 1 μPa2.

Acoustic detectability of whales amidst underwater noise off the west coast of South Africa

Anthropogenic underwater noise has been shown to negatively affect marine organisms globally; yet little to no noise research has been conducted in most African waters including South Africa's. This study aimed to quantitatively describe sources of underwater noise and effects of underwater noise on the acoustic detectability of Antarctic blue, fin, minke, humpback, and sperm whales off South Africa's west coast. Noise from vessel traffic (<35 km to the location of recorders) dominated the soundscape below 500 Hz while wind-generated noise increased with wind speed above 5 m s^-1 and dominated the soundscape above 500 Hz. Acoustic detectability of humpback, minke and sperm whales decreased with increasing ambient noise levels whereas blue and fin whale acoustic detectability increased with the ambient noise levels. We provide baseline information on underwater noise sources and the effects of underwater noise on whale acoustic detectability off the west coast of South Africa.

Maximum likelihood separation of anthropogenic and wind-generated underwater noise

A method is presented for simultaneous estimation of the probability distributions of both anthropogenic and wind-generated underwater noise power spectral density using only acoustic data recorded with a single hydrophone. Probability density models for both noise sources are suggested, and the model parameters are estimated using the method of maximum likelihood. A generic mixture model is utilized to model a time invariant anthropogenic noise distribution. Wind-generated noise is assumed normally distributed with a wind speed-dependent mean. The mean is then modeled as an affine linear function of the wind-generated noise level at a reference frequency, selected in a frequency range where the anthropogenic noise is less dominant. The method was used to successfully estimate the wind-generated noise spectra from ambient noise recordings collected at two locations in the southern Baltic Sea. At the North location, 3 km from the nearest shipping lane, the ship noise surpasses the wind-generated noise almost 100% of the time in the frequency band 63-400 Hz during summer for wind speed 7 m/s. At the South location, 14 km to the nearest shipping lane, the ship noise dominance is lower but still 40%-90% in the same frequencies and wind speed.

An overview of ambient sound using Ocean Observatories Initiative hydrophones

The Ocean Observatories Initiative (OOI) sensor network provides a unique opportunity to study ambient sound in the north-east Pacific Ocean. The OOI sensor network has five low frequency (Fs = 200 Hz) and six broadband (Fs = 64 kHz) hydrophones that have been recording ambient sound since 2015. In this paper, we analyze acoustic data from 2015 to 2020 to identify prominent features that are present in the OOI acoustic dataset. Notable features in the acoustic dataset that are highlighted in this paper include volcanic and seismic activity, rain and wind noise, marine mammal vocalizations, and anthropogenic sound, such as shipping noise. For all low frequency hydrophones and four of the six broadband hydrophones, we will present long-term spectrograms, median time-series trends for different spectral bands, and different statistical metrics about the acoustic environment. We find that 6-yr acoustic trends vary, depending on the location of the hydrophone and the spectral band that is observed. Over the course of six years, increases in spectral levels are seen in some locations and spectral bands, while decreases are seen in other locations and spectral bands. Last, we discuss future areas of research to which the OOI dataset lends itself.

Underwater Sound Characteristics of a Ship with Controllable Pitch Propeller

The time-dependent spectral characteristics of underwater sound radiated by an oceanic vessel have complex dependencies on ship machinery, propeller dynamics, and the hydrodynamics of the ship exhaust and motion, as well as onboard activities. Here, the underwater sound radiated by a ship equipped with a controllable pitch propeller (CPP) is analyzed and quantified via its (i) power spectral density for signal energetics, (ii) temporal coherence for machinery tonal sound, and (iii) spectral coherence for propeller amplitude-modulated cavitation noise. Frequency-modulated (FM) tonal signals are also characterized in terms of their frequency variations. These characteristics are compared for different propeller pitch ratios, ranging from 20% to 82% at a fixed number of propeller revolutions per minute (RPM). The efficacy and robustness of ship parameter estimation at different pitches are discussed. Finally, an analysis of one special measurement is provided: propeller pitch and RPM over the duration of the measurement when the ship changes speed. The 50% pitch was found to be a crucial point for this ship, around which the tonal characteristics of its underwater radiated sound attain their peak values while broadband sound and associated spectral coherences are at a minimum. The findings here elucidate the effects of pitch variation on underwater sound radiated by ships with controllable pitch propellers and has applications in ship design and underwater noise mitigation.

Anthropogenic sound field and noise mapping in an Arctic fjord during summer

Sound Pressure Levels were recorded using an Automated Noise Measurement System, during July 2015 - April 2016 at the Kongsfjorden, Arctic. The fjord houses the NyAlesund port and has many vessels plying during summer, which contributes to anthropogenic noise. Spectral distribution and average sound level at 1/3-octave band from 63 Hz to 5000 Hz has been analyzed and correlated with Automatic Identification System marine traffic data. The radiated acoustic field from vessel transits has been predicted through source level modeling for different category vessels. Further, an acoustic propagation model MMPE based on Parabolic Equation method has been used to evaluate range dependent propagation along the fjord and Transmission Loss estimates have been calculated for upslope and down slope cases. Noise due to shipping has been estimated using Source-Path-Receiver Model using Propagation Loss model estimates, Sound Pressure Level, and Source Level predictions. Noise maps with level contours are generated for shipping, depicting the maximum sound levels for the Kongsfjorden.

Potential for acoustic masking due to shipping noise in the European lobster (Homarus gammarus)

Marine traffic is the most pervasive underwater anthropogenic noise pollution which can mask acoustic communication in marine mammals and fish, but its effect in marine invertebrates remains unknown. Here, we performed an at sea experiment to study the potential of shipping noise to mask and alter lobster acoustic communication. We used hydrophones to record buzzing sounds and accelerometers to detect lobster carapace vibrations (i.e. the buzzing sounds' sources). We demonstrated that male individuals produced carapace vibrations under various ambient noise conditions, including heavy shipping noise. However, while the associated waterborne buzzing sounds could be recorded under natural ambient noise levels, they were masked by shipping noise. Additionally, lobsters significantly increased their call rates in presence of shipping noise, suggesting a vocal compensation due to the reduction of intraspecific communication. This study reports for the first time the potential acoustic masking of lobster acoustic communication by chronic anthropogenic noise pollution, which could affect ecologically important behaviors.

Underwater soundscape description from cyclostationarity point of view

The description of underwater soundscape is central to the understanding of the marine environment, both from the standpoint of the fauna and anthropic activities and its interactions with the atmosphere. Some of these sources produce signals whose patterns are periodically repeated over time (i.e., ship propellers in motion, odontocetes clicks, snapping shrimp, noise emanating from surface waves, etc.). As ocean noise is a combination of various sources sometimes sharing the same frequency band, it is necessary to develop efficient algorithms to process the increasingly voluminous data acquired. To this end, the theory of cyclostationarity is adopted as an effective tool for exposing hidden periodicities in low signal to noise ratio. This theory, widely used to analyze mechanical systems or communications, is extended and applied on underwater soundscapes. The method is demonstrated using data recorded in the Celtic Sea at the French coast of Brittany with practical experiments using field measurements obtained from recording stations.

Spatiotemporal patterns in the natural and anthropogenic additions to the soundscape in parts of the Salish Sea, British Columbia, 2018-2020

Passive acoustic recorders were deployed over two years (February 2018-March 2020) in the Salish Sea to monitor the underwater soundscape. Seasonal cycles and differences between the open Strait of Juan de Fuca and protected inner waterways were pervasive during this period. A comparison between natural and human-derived noise demonstrated the impact of anthropogenic activities on the sound field. Elevated ambient noise levels during winter resulted predominantly from greater sea states and storm events. Abiotic additions were defined through correlations to wind speed, wave and precipitation measures. Vessel noise was a pervasive anthropogenic addition; commercial vessel noise was consistently present, whereas smaller vessels showed weekly and diurnal patterns, especially during the summer when their presence increased. A better understanding of the different soundscape constituents, and when each dominates, is crucial to understanding the human impact on underwater ecosystems and the organisms within them, leading to more effective mitigation measures.

Temporal variation of the underwater soundscape in Jiaotou Bay, an Indo-Pacific humpback dolphin (Sousa chinensis) habitat off Hainan Island, China

The underwater soundscape is an important ecological element affecting numerous aquatic animals, in particular dolphins, which must identify salient cues from ambient ocean noise. In this study, temporal variations in the soundscape of Jiaotou Bay were monitored from February 2016 to January 2017, where a population of Indo-Pacific humpback dolphins (Sousa chinensis) has recently been a regular sighting. An autonomous acoustic recorder was deployed in shallow waters, and 1/3-octave band sound pressure levels (SPLs) were calculated with central frequencies ranging from 25 Hz to 40 kHz, then were grouped into 3 subdivided bands via cluster analysis. SPLs at each major band showed significant differences on a diel, fishing-related period, seasonal, and tidal phase scale. Anthropogenic noise generated by passing ships and underwater explosions were recorded in the study area. The fish and dolphin acoustic activities both exhibited diel and seasonal variations, but no tidal cycle patterns. A negative significant relationship between anthropogenic sound detection rates and dolphin detection rates were observed, and fish detection rates showed no effect on dolphin detection rates, indicating anthropogenic activity avoidance and no forced foraging in dolphins in the study area. The results provide fundamental insight into the acoustic dynamics of an important Indo-Pacific humpback dolphin habitat within a coastal area affected by a rapid increase in human activity, and demonstrate the need to protect animal habitat from anthropogenic noises.

Quantifying the contribution of ship noise to the underwater sound field

The ambient sound field in the ocean can be decomposed into a linear combination of two independent fields attributable to wind-generated wave action at the surface and noise radiated by ships. The vertical coherence (the cross-spectrum normalized by the power spectra) and normalized directionality of wind-generated noise in the ocean are stationary in time, do not vary with source strength and spectral characteristics, and depend primarily on the local sound speed and the geoacoustic properties which define the propagation environment. The contribution to the noise coherence due to passing vessels depends on the range between the source and receiver, the propagation environment, and the effective bandwidth of the characteristic source spectrum. Using noise coherence models for both types of the sources, an inversion scheme is developed for the relative and absolute contribution of frequency dependent ship noise to the total sound field. A month-long continuous ambient sound recording collected on a pair of vertically aligned hydrophones near Alvin Canyon at the New England shelf break is decomposed into time-dependent ship noise and wind-driven noise power spectra. The processing technique can be used to quantify the impact of human activity on the sound field above the natural dynamic background noise, or to eliminate ship noise from a passive acoustic monitoring data set.

Long-Range Automatic Detection, Acoustic Signature Characterization and Bearing-Time Estimation of Multiple Ships with Coherent Hydrophone Array

Three approaches for instantaneous wide-area analysis of ship-radiated underwater sound, each focusing on a different aspect of that sound, received on a large-aperture densely-sampled coherent hydrophone array have been developed. (i) Ship’s narrowband machinery tonal sound is analyzed via temporal coherence using Mean Magnitude-Squared Coherence (MMSC) calculations. (ii) Ship’s broadband amplitude-modulated cavitation noise is examined using Cyclic Spectral Coherence (CSC) analysis that provides estimates for propeller blade pass rotation frequency, shaft rotation frequency, and hence the number of propeller blades. (iii) Mean power spectral densities (PSD) averaged across broad bandwidths are calculated in order to detect acoustically energetic ships. Each of these techniques are applied after beamforming of the received acoustic signals on a coherent hydrophone array, leading to significantly enhanced signal-to-noise ratios for simultaneous detection, bearing-time estimation and acoustic signature characterization of multiple ships over continental-shelf scale regions. The approaches are illustrated with underwater recordings of a 160-element coherent hydrophone array for six ocean vessels, that are located at a variety of bearings and ranges out to 200 km from the array, in the Norwegian Sea in February 2014. The CSC approach is shown to also be useful for automatic detection and bearing-time estimation of repetitive marine mammal vocalizations, providing estimates for inter-pulse-train and inter-pulse intervals from CSC spectra cyclic fundamental and first recurring peak frequencies respectively.

Predicting the exposure of diving grey seals to shipping noise

There is high spatial overlap between grey seals and shipping traffic, and the functional hearing range of grey seals indicates sensitivity to underwater noise emitted by ships. However, there is still very little data regarding the exposure of grey seals to shipping noise, constraining effective policy decisions. Particularly, there are few predictions that consider the at-sea movement of seals. Consequently, this study aimed to predict the exposure of adult grey seals and pups to shipping noise along a three-dimensional movement track, and assess the influence of shipping characteristics on sound exposure levels. Using ship location data, a ship source model, and the acoustic propagation model, RAMSurf, this study estimated weighted 24-h sound exposure levels (10-1000 Hz) (SEL_w). Median predicted 24-h SEL_w was 128 and 142 dB re 1 μPa²s for the pups and adults, respectively. The predicted exposure of seals to shipping noise did not exceed best evidence thresholds for temporary threshold shift. Exposure was mediated by the number of ships, ship source level, the distance between seals and ships, and the at-sea behaviour of the seals. The results can inform regulatory planning related to anthropogenic pressures on seal populations.

Underwater radiated noise from hydrofoils in coastal water

Underwater noise from commercial shipping throughout the oceans has been increasing over the past decades and the environmental impact of this noise remains an area of great uncertainty. This has led to the measurement of noise from commercial vessels in order to understand the impacts that these vessels may engender. Hydrofoils are used by ferries in various locations around the world and locally may be a significant contributing factor of the soundscape. However, the investigation on underwater radiated noise from the activity of hydrofoils in the field has not been widely conducted. This article is an attempt to characterize the noise from hydrofoils in the field. Detailed measurements in the coastal water close to the Panarea port, Italy are reported. The investigation describes the broadband frequency spectrum with the main energy approximately centered on 30-130 Hz but covering frequencies up to tens of kHz. A key result was that the spectrum of the noise varied between the three stages (displacement, transition, and foiling) of the hydrofoils heading into or out of the port.

Recreational vessels without Automatic Identification System (AIS) dominate anthropogenic noise contributions to a shallow water soundscape

Recreational boating is an increasing activity in coastal areas and its spatiotemporal overlap with key habitats of marine species pose a risk for negative noise impacts. Yet, recreational vessels are currently unaccounted for in vessel noise models using Automatic Identification System (AIS) data. Here we conduct a case study investigating noise contributions from vessels with and without AIS (non-AIS) in a shallow coastal area within the Inner Danish waters. By tracking vessels with theodolite and AIS, while recording ambient noise levels, we find that non-AIS vessels have a higher occurrence (83%) than AIS vessels, and that motorised recreational vessels can elevate third-octave band noise centred at 0.125, 2 and 16 kHz by 47-51 dB. Accordingly, these vessels dominated the soundscape in the study site due to their high numbers, high speeds and proximity to the coast. Furthermore, recreational vessels caused 49-85% of noise events potentially eliciting behavioural responses in harbour porpoises (AIS vessels caused 5-24%). We therefore conclude that AIS data would poorly predict vessel noise pollution and its impacts in this and other similar marine environments. We suggest to improve vessel noise models and impact assessments by requiring that faster and more powerful recreational vessels carry AIS-transmitters.

Spatial and Temporal Variability of Ambient Underwater Sound in the Baltic Sea

During last decades, anthropogenic underwater sound and its chronic impact on marine species have been recognised as an environmental protection challenge. At the same time, studies on the spatial and temporal variability of ambient sound, and how it is affected by biotic, abiotic and anthropogenic factors are lacking. This paper presents analysis of a large-scale and long-term underwater sound monitoring in the Baltic Sea. Throughout the year 2014, sound was monitored in 36 Baltic Sea locations. Selected locations covered different natural conditions and ship traffic intensities. The 63 Hz, 125 Hz and 2 kHz one-third octave band sound pressure levels were calculated and analysed. The levels varied significantly from one monitoring location to another. The annual median sound pressure level of the quietest and the loudest location differed almost 50 dB in the 63 Hz one-third octave band. Largest difference in the monthly medians was 15 dB in 63 Hz one-third octave band. The same monitoring locations annual estimated probability density functions for two yearly periods show strong similarity. The data variability grows as the averaging time period is reduced. Maritime traffic elevates the ambient sound levels in many areas of the Baltic Sea during extensive time periods.

Ecology of fish hearing

Underwater sound is directional and can convey important information about the surrounding environment or the animal emitting the sound. Therefore, sound is a major sensory channel for fishes and plays a key role in many life-history strategies. The effect of anthropogenic noise on aquatic life, which may be causing homogenisation or fragmentation of biologically important signals underwater is of growing concern. In this review we discuss the role sound plays in the ecology of fishes, basic anatomical and physiological adaptations for sound reception and production, the effects of anthropogenic noise and how fishes may be coping to changes in their environment, to put the ecology of fish hearing into the context of the modern underwater soundscape.

Whistles emitted by Indo-Pacific humpback dolphins (Sousa chinensis) in Zhanjiang waters, China

Whistles emitted by Indo-Pacific humpback dolphins in Zhanjiang waters, China, were collected by using autonomous acoustic recorders. A total of 529 whistles with clear contours and signal-to-noise ratio higher than 10 dB were extracted for analysis. The fundamental frequencies and durations of analyzed whistles were in ranges of 1785-21 675 Hz and 30-1973 ms, respectively. Six tonal types were identified: constant, downsweep, upsweep, concave, convex, and sine whistles. Constant type was the most dominant tonal type, accounting for 32.51% of all whistles, followed by sine type, accounting for 19.66% of all whistles. This paper examined 17 whistle parameters, which showed significant differences among the six tonal types. Whistles without inflections, gaps, and stairs accounted for 62.6%, 80.6%, and 68.6% of all whistles, respectively. Significant intraspecific differences in all duration and frequency parameters of dolphin whistles were found between this study and the study in Malaysia. Except for start frequency, maximum frequency and the number of harmonics, all whistle parameters showed significant differences between this study and the study conducted in Sanniang Bay, China. The intraspecific differences in vocalizations for this species may be related to macro-geographic and/or environmental variations among waters, suggesting a potential geographic isolation among populations of Indo-Pacific humpback dolphins.

Harbour porpoise responses to pile-driving diminish over time

Estimating impacts of offshore windfarm construction on marine mammals requires data on displacement in relation to different noise levels and sources. Using echolocation detectors and noise recorders, we investigated harbour porpoise behavioural responses to piling noise during the 10-month foundation installation of a North Sea windfarm. Current UK guidance assumes total displacement within 26 km of pile driving. By contrast, we recorded a 50% probability of response within 7.4 km (95% CI = 5.7-9.4) at the first location piled, decreasing to 1.3 km (95% CI = 0.2-2.8) by the final location; representing 28% (95% CI = 21-35) and 18% (95% CI = 13-23) displacement of individuals within 26 km. Distance proved as good a predictor of responses as audiogram-weighted received levels, presenting a more practicable variable for environmental assessments. Critically, acoustic deterrent device (ADD) use and vessel activity increased response levels. Policy and management to minimize impacts of renewables on cetaceans have concentrated on pile-driving noise. Our results highlight the need to consider trade-offs between efforts to reduce far-field behavioural disturbance and near-field injury through ADD use.

Detection, Localization and Classification of Multiple Mechanized Ocean Vessels over Continental-Shelf Scale Regions with Passive Ocean Acoustic Waveguide Remote Sensing

Multiple mechanized ocean vessels, including both surface ships and submerged vehicles, can be simultaneously monitored over instantaneous continental-shelf scale regions >10,000 km 2 via passive ocean acoustic waveguide remote sensing. A large-aperture densely-sampled coherent hydrophone array system is employed in the Norwegian Sea in Spring 2014 to provide directional sensing in 360 degree horizontal azimuth and to significantly enhance the signal-to-noise ratio (SNR) of ship-radiated underwater sound, which improves ship detection ranges by roughly two orders of magnitude over that of a single hydrophone. Here, 30 mechanized ocean vessels spanning ranges from nearby to over 150 km from the coherent hydrophone array, are detected, localized and classified. The vessels are comprised of 20 identified commercial ships and 10 unidentified vehicles present in 8 h/day of Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS) observation for two days. The underwater sounds from each of these ocean vessels received by the coherent hydrophone array are dominated by narrowband signals that are either constant frequency tonals or have frequencies that waver or oscillate slightly in time. The estimated bearing-time trajectory of a sequence of detections obtained from coherent beamforming are employed to determine the horizontal location of each vessel using the Moving Array Triangulation (MAT) technique. For commercial ships present in the region, the estimated horizontal positions obtained from passive acoustic sensing are verified by Global Positioning System (GPS) measurements of the ship locations found in a historical Automatic Identification System (AIS) database. We provide time-frequency characterizations of the underwater sounds radiated from the commercial ships and the unidentified vessels. The time-frequency features along with the bearing-time trajectory of the detected signals are applied to simultaneously track and distinguish these vessels.

Boat noise in an estuarine soundscape - A potential risk on the acoustic communication and reproduction of soniferous fish in the May River, South Carolina

The impact of boat related noise on marine life is a subject of concern, particularly for fish species that utilize acoustic communication for spawning purposes. The goal of this study was to quantify and examine the risk of boat noise on fish acoustic communication by performing acoustic monitoring of the May River, South Carolina (USA) from February to November 2013 using DSG-Ocean recorders. The number of boats detected increased from the source to the mouth with the highest detections near the Intracoastal Waterway (ICW). Boat noise frequency ranges overlapped with courtship sounds of silver perch (Bairdiella chrysoura), black drum (Pogonias cromis), oyster toadfish (Opsanus tau), spotted seatrout (Cynoscion nebulosus), and red drum (Sciaenops ocellatus). In the May River estuary, red drum may experience the greatest risk of auditory masking because of late afternoon choruses (21% time overlap with boat noise) and only one spawning location near the noisy ICW.

Vessel noise cuts down communication space for vocalizing fish and marine mammals

Anthropogenic noise across the world's oceans threatens the ability of vocalizing marine species to communicate. Some species vocalize at key life stages or whilst foraging, and disruption to the acoustic habitat at these times could lead to adverse consequences at the population level. To investigate the risk of these impacts, we investigated the effect of vessel noise on the communication space of the Bryde's whale Balaenoptera edeni, an endangered species which vocalizes at low frequencies, and bigeye Pempheris adspersa, a nocturnal fish species which uses contact calls to maintain group cohesion while foraging. By combining long-term acoustic monitoring data with AIS vessel-tracking data and acoustic propagation modelling, the impact of vessel noise on their communication space was determined. Routine vessel passages cut down communication space by up to 61.5% for bigeyes and 87.4% for Bryde's whales. This influence of vessel noise on communication space exceeded natural variability for between 3.9 and 18.9% of the monitoring period. Additionally, during the closest point of approach of a large commercial vessel, <10 km from the listening station, the communication space of both species was reduced by a maximum of 99% compared to the ambient soundscape. These results suggest that vessel noise reduces communication space beyond the evolutionary context of these species and may have chronic effects on these populations. To combat this risk, we propose the application or extension of ship speed restrictions in ecologically significant areas, since our results indicate a reduction in sound source levels for vessels transiting at lower speeds.

The underwater acoustic environment at SGaan Kinghlas-Bowie Seamount Marine Protected Area: Characterizing vessel traffic and associated noise using satellite AIS and acoustic datasets

Vessel traffic is one of the most wide-spread anthropogenic contributors to ocean noise worldwide and has the potential to alter ecosystems upon which cetaceans and other acoustically sensitive marine organisms rely. Canada's SGaan Kinghlas-Bowie Seamount Marine Protected Area (SK-B MPA) is one such area whose productive ecosystem could benefit from greater monitoring of human induced threats in order to inform management. Despite earning official designation as a Marine Protected Area under the Oceans Act in 2008, little remains known about vessel traffic in the region and the associated potential impacts on vulnerable marine species. Therefore, to increase our understanding of vessel traffic and accompanying noise at SK-B MPA, satellite AIS and acoustic data were investigated. The results of this study suggest that variations in ambient sound levels in the region are driven by near and distant shipping events, thus having implications for future management of the MPA.

Passive, broadband suppression of radiation of low-frequency sound

Anthropogenic noise pollution of the ocean is an acute and growing problem. This letter explores one possible mechanism of noise abatement. The far-field acoustic pressure due to a compact underwater source can be suppressed by placing a small compliant body in the vicinity of the source. Here, the feasibility and efficiency of the suppression are evaluated by quantifying the reduction in radiated acoustic energy for several simple geometries, which include sound sources in an unbounded fluid, near a reflecting boundary, or in a shallow-water waveguide. The analysis is streamlined using analytic solutions for sound diffraction by simple shapes.

Ambient noise dynamics in a heavy shipping area

The management of underwater noise within the European Union's waters is a significant component (Descriptor 11) of the Marine Strategy Framework Directive (MSFD). The indicator related to continuous noise, is the noise levels in two one-third octave bands centered at 63Hz and 125Hz. This paper presents an analysis of underwater noise in the Celtic Sea, a heavy shipping area which also hosts the seasonal Ushant thermal front. In addition to the MSFD recommended frequency bands, the analysis was extended to lower and upper frequency bands. Temporal and spatial variations as well as the influence of the properties of the water column on the noise levels were assessed. The noise levels in the area had a high dynamic range and generally exceeded 100dB re 1μPa. Finally, the results highlighted that oceanic mooring must be designed to minimize the pseudo-noise and consider the water column physical properties.

Broadband ship noise and its potential impacts on Indo-Pacific humpback dolphins: Implications for conservation and management

Ship noise pollution has raised considerable concerns among regulatory agencies and cetacean researchers worldwide. There is an urgent need to quantify ship noise in coastal areas and assess its potential biological impacts. In this study, underwater broadband noise from commercial ships in a critical habitat of Indo-Pacific humpback dolphins was recorded and analyzed. Data analysis indicated that the ship noise caused by the investigated commercial ships with an average length of 134 ± 81 m, traveling at 18.8 ± 2.5 km/h [mean ± standard deviation (SD), n = 21] comprises mid-to-high components with frequencies approaching and exceeding 100 kHz, and the ship noise could be sensed auditorily by Indo-Pacific humpback dolphins within most of their sensitive frequency range. The contributions of ship noise to ambient noise were highest in two third-octave bands with center frequencies of 8 and 50 kHz, which are within the sensitive hearing range of Indo-Pacific humpback dolphins and overlap the frequency of sounds that are biologically significant to the dolphins. It is estimated that ship noise in these third-octave bands can be auditorily sensed by and potentially affect the dolphins within 2290 ± 1172 m and 848 ± 358 m (mean ± SD, n = 21), respectively.

Continuous monitoring of noise levels in the Gulf of Catania (Ionian Sea). Study of correlation with ship traffic

Acoustic noise levels were measured in the Gulf of Catania (Ionian Sea) from July 2012 to May 2013 by a low frequency (<1000Hz) hydrophone, installed on board the NEMO-SN1 multidisciplinary observatory. NEMO-SN1 is a cabled node of EMSO-ERIC, which was deployed at a water depth of 2100m, 25km off Catania. The study area is characterized by the proximity of mid-size harbors and shipping lanes. Measured noise levels were correlated with the passage of ships tracked with a dedicated AIS antenna. Noise power was measured in the frequency range between 10Hz and 1000Hz. Experimental data were compared with the results of a fast numerical model based on AIS data to evaluate the contribution of shipping noise in six consecutive 1/3 octave frequency bands, including the 1/3 octave frequency bands centered at 63Hz and 125Hz, indicated by the Marine Strategy Framework Directive (2008/56/EC).

Shipping noise in a dynamic sea: a case study of grey seals in the Celtic Sea

Shipping noise is a threat to marine wildlife. Grey seals are benthic foragers, and thus experience acoustic noise throughout the water column, which makes them a good model species for a case study of the potential impacts of shipping noise. We used ship track data from the Celtic Sea, seal track data and a coupled ocean-acoustic modelling system to assess the noise exposure of grey seals along their tracks. It was found that the animals experience step changes in sound levels up to ~20dB at a frequency of 125Hz, and ~10dB on average over 10-1000Hz when they dive through the thermocline, particularly during summer. Our results showed large seasonal differences in the noise level experienced by the seals. These results reveal the actual noise exposure by the animals and could help in marine spatial planning.

Underwater noise levels in UK waters

Underwater noise from human activities appears to be rising, with ramifications for acoustically sensitive marine organisms and the functioning of marine ecosystems. Policymakers are beginning to address the risk of ecological impact, but are constrained by a lack of data on current and historic noise levels. Here, we present the first nationally coordinated effort to quantify underwater noise levels, in support of UK policy objectives under the EU Marine Strategy Framework Directive (MSFD). Field measurements were made during 2013–2014 at twelve sites around the UK. Median noise levels ranged from 81.5–95.5 dB re 1 μPa for one-third octave bands from 63–500 Hz. Noise exposure varied considerably, with little anthropogenic influence at the Celtic Sea site, to several North Sea sites with persistent vessel noise. Comparison of acoustic metrics found that the RMS level (conventionally used to represent the mean) was highly skewed by outliers, exceeding the 97^th percentile at some frequencies. We conclude that environmental indicators of anthropogenic noise should instead use percentiles, to ensure statistical robustness. Power analysis indicated that at least three decades of continuous monitoring would be required to detect trends of similar magnitude to historic rises in noise levels observed in the Northeast Pacific.

Long-term underwater sound measurements in the shipping noise indicator bands 63Hz and 125Hz from the port of Falmouth Bay, UK

Chronic low-frequency anthropogenic sound, such as shipping noise, may be negatively affecting marine life. The EU's Marine Strategy Framework Directive (MSFD) includes a specific indicator focused on this noise. This indicator is the yearly average sound level in third-octave bands with centre frequencies at 63Hz and 125Hz. These levels are described for Falmouth Bay, UK, an active port at the entrance to the English Channel. Underwater sound was recorded for 30min h(-1) over the period June 2012 to November 2013 for a total of 435days. Mean third-octave levels were louder in the 125-Hz band (annual mean level of 96.0dB re 1μPa) than in the 63-Hz band (92.6dB re 1 μPa). These levels and variations are assessed as a function of seasons, shipping activity and wave height, providing comparison points for future monitoring activities, including the MSFD and emerging international regulation.

Analysis and modeling of 255 source levels of merchant ships from an acoustic observatory along St. Lawrence Seaway

An ensemble of 255 spectral source levels (SSLs) of merchant ships were measured with an opportunistic seaway acoustic observatory adhering to the American National Standards Institute/Acoustical Society of America S12.64-2009 standard as much as possible, and deployed in the 350-m deep lower St. Lawrence Seaway in eastern Canada. The estimated SSLs were sensitive to the transmission loss model. The best transmission loss model at the three measuring depths was an empirical in situ function for ranges larger than 300 m, fused with estimates from a wavenumber integration propagation model fed with inverted local geoacoustic properties for [300 to 1 m] ranges. Resulting SSLs still showed a high variability. Uni- and multi-variate analyses showed weak intermingled relations with ship type, length, breadth, draught, speed, age, and other variables. Cluster analyses distinguished six different SSL patterns, which did not correspond to distinctive physical characteristics of the ships. The broadband [20-500 Hz] source levels varied by 30 dB or more within all four 50-m length categories. Common SSL models based on frequency, length and speed failed to unbiasly replicate the observations. This article presents unbiased SSL models that explain 75%-88% of the variance using frequency, ship speed, and three other automatic identification system ship characteristics.

Underwater soundscape of marine protected areas in the south Brazilian coast

The Laje de Santos Marine State Park (LSMSP) and Xixová-Japuí State Park (XJSP) are two protected areas (PA), close to the Santos Bay in the south Brazilian coast. The region encompasses both important biodiversity and anthropogenic activities. This study aims to serve as a first reference survey of the underwater soundscape of these PAs. Additionally it evaluates the presence of the anthropogenic and biological sound in these areas. One month of continuous recorded underwater sound, at selected locations in XJSP and LSMSP, is used in this study. The data were characterized by its spectral content and by the temporal evolution of Sound Pressure Levels (SPL). Both locations showed sound events with daily periodicities, mainly related with boats and fish chorus.

Short- and long-term monitoring of underwater sound levels in the Hudson River (New York, USA)

There is a growing body of research on natural and man-made sounds that create aquatic soundscapes. Less is known about the soundscapes of shallow waters, such as in harbors, rivers, and lakes. Knowledge of soundscapes is needed as a baseline against which to determine the changes in noise levels resulting from human activities. To provide baseline data for the Hudson River at the site of the Tappan Zee Bridge, 12 acoustic data loggers were deployed for a 24-h period at ranges of 0-3000 m from the bridge, and four of the data loggers were re-deployed for three months of continuous recording. Results demonstrate that this region of the river is relatively quiet compared to open ocean conditions and other large river systems. Moreover, the soundscape had temporal and spatial diversity. The temporal patterns of underwater noise from the bridge change with the cadence of human activity. Bridge noise (e.g., road traffic) was only detected within 300 m; farther from the bridge, boating activity increased sound levels during the day, and especially on the weekend. Results also suggest that recording near the river bottom produced lower pseudo-noise levels than previous studies that recorded in the river water column.

Soundscape and Noise Exposure Monitoring in a Marine Protected Area Using Shipping Data and Time-Lapse Footage

We review recent work that developed new techniques for underwater noise assessment that integrate acoustic monitoring with automatic identification system (AIS) shipping data and time-lapse video, meteorological, and tidal data. Two sites were studied within the Moray Firth Special Area of Conservation (SAC) for bottlenose dolphins, where increased shipping traffic is expected from construction of offshore wind farms outside the SAC. Noise exposure varied markedly between the sites, and natural and anthropogenic contributions were characterized using multiple data sources. At one site, AIS-operating vessels accounted for total cumulative sound exposure (0.1-10 kHz), suggesting that noise modeling using the AIS would be feasible.

Underwater Sound Levels at a Wave Energy Device Testing Facility in Falmouth Bay, UK

Passive acoustic monitoring devices were deployed at FaBTest in Falmouth Bay, UK, a marine renewable energy device testing facility during trials of a wave energy device. The area supports considerable commercial shipping and recreational boating along with diverse marine fauna. Noise monitoring occurred during (1) a baseline period, (2) installation activity, (3) the device in situ with inactive power status, and (4) the device in situ with active power status. This paper discusses the preliminary findings of the sound recording at FabTest during these different activity periods of a wave energy device trial.

Dynamics of soundscape in a shallow water marine environment: a study of the habitat of the Indo-Pacific humpback dolphin

The underwater acoustic field is an important ecological element for many aquatic animals. This research examines the soundscape of a critically endangered Indo-Pacific humpback dolphin population in the shallow water environment off the west coast of Taiwan. Underwater acoustic recordings were conducted between late spring and late fall in 2012 at Yunlin (YL), which is close to a shipping lane, and Waisanding (WS), which is relatively pristine. Site-specific analyses were performed on the dynamics of the temporal and spectral acoustic characteristics for both locations. The results highlight the dynamics of the soundscape in two major octave bands: 150-300 Hz and 1.2-2.4 kHz. The acoustic energy in the former frequency band is mainly associated with passing container vessels near YL, while the latter frequency band is from sonic fish chorus at nighttime in both recording sites. In addition, large variation of low frequency acoustic energy throughout the study period was noticed at WS, where the water depths ranged between 1.5 and 4.5 m depending on tidal cycle. This phenomenon suggests that besides certain sound sources in the environment, the coastal soundscape may also be influenced by its local bathymetry and the dynamics of the physical environment.

Monitoring ship noise to assess the impact of coastal developments on marine mammals

The potential impacts of underwater noise on marine mammals are widely recognised, but uncertainty over variability in baseline noise levels often constrains efforts to manage these impacts. This paper characterises natural and anthropogenic contributors to underwater noise at two sites in the Moray Firth Special Area of Conservation, an important marine mammal habitat that may be exposed to increased shipping activity from proposed offshore energy developments. We aimed to establish a pre-development baseline, and to develop ship noise monitoring methods using Automatic Identification System (AIS) and time-lapse video to record trends in noise levels and shipping activity. Our results detail the noise levels currently experienced by a locally protected bottlenose dolphin population, explore the relationship between broadband sound exposure levels and the indicators proposed in response to the EU Marine Strategy Framework Directive, and provide a ship noise assessment toolkit which can be applied in other coastal marine environments.

Averaging underwater noise levels for environmental assessment of shipping

Rising underwater noise levels from shipping have raised concerns regarding chronic impacts to marine fauna. However, there is a lack of consensus over how to average local shipping noise levels for environmental impact assessment. This paper addresses this issue using 110 days of continuous data recorded in the Strait of Georgia, Canada. Probability densities of ~10(7) 1-s samples in selected 1/3 octave bands were approximately stationary across one-month subsamples. Median and mode levels varied with averaging time. Mean sound pressure levels averaged in linear space, though susceptible to strong bias from outliers, are most relevant to cumulative impact assessment metrics.