Particle motion measured at an operational wind turbine in relation to hearing sensitivity in fish

Low-frequency band noise generated by industrial recirculating aquaculture systems exhibits a greater impact on Micropterus salmoidess

The effect of underwater noise environment generated by equipment in industrial recirculating aquaculture systems (RAS) on fish is evident. However, different equipment generate noise in various frequency ranges. Understanding the effects of different frequency ranges noise on cultured species is important for optimizing the underwater acoustic environment in RAS. Given this, the effects of underwater noise across various frequency bands in RAS on the growth, physiology, and collective behavior of juvenile largemouth bass (Micropterus salmoides) were comprehensively evaluated here. In this study, three control groups were established: low-frequency noise group (80-1000 Hz, 117 dB re 1μPa RMS), high-frequency noise group (1-19 kHz, 117 dB re 1μPa RMS), and ambient group. During a 30-day experiment, it was found that: 1) industrial RAS noise with different frequency bands all had a certain inhibitory effect on the growth of fish, which the weight gain rate and product of length and depth of caudal peduncle in the ambient group were significantly higher than those of the two noise groups, with the low-frequency noise group showing significantly lower values than the high-frequency noise group; 2) industrial RAS noise had a certain degree of adverse effect on the digestive ability of fish, with the low-frequency noise group being more affected; 3) industrial RAS noise affected the collective feeding behavior of fish, with the collective feeding signal propagation efficiency and feeding intensity of the noise groups being significantly lower than those of the ambient group, and the high-frequency noise group performing better than the low-frequency noise group as a whole therein. From the above, the underwater noise across different frequency bands generated by equipment operation in industrial RAS both had an impact on juvenile largemouth bass, with the low-frequency noise group being more severely affected.

Soundscapes as heard by invertebrates and fishes: Particle motion measurements on coral reefs

Coral reef soundscapes are increasingly studied for their ecological uses by invertebrates and fishes, for monitoring habitat quality, and to investigate effects of anthropogenic noise pollution. Few examinations of aquatic soundscapes have reported particle motion levels and variability, despite their relevance to invertebrates and fishes. In this study, ambient particle acceleration was quantified from orthogonal hydrophone arrays over several months at four coral reef sites, which varied in benthic habitat and fish communities. Time-averaged particle acceleration magnitudes were similar across axes, within 3 dB. Temporal trends of particle acceleration corresponded with those of sound pressure, and the strength of diel trends in both metrics significantly correlated with percent coral cover. Higher magnitude particle accelerations diverged further from pressure values, potentially representing sounds recorded in the near field. Particle acceleration levels were also reported for boat and example fish sounds. Comparisons with particle acceleration derived audiograms suggest the greatest capacity of invertebrates and fishes to detect soundscape components below 100 Hz, and poorer detectability of soundscapes by invertebrates compared to fishes. Based on these results, research foci are discussed for which reporting of particle motion is essential, versus those for which sound pressure may suffice.

Particle motion observed during offshore wind turbine piling operation

Measurement of particle motion from an offshore piling event in the North was conducted to determine noise levels. For this purpose, a bespoken sensor was developed that was both autonomous and sensitive up to 2 kHz. The measurement was undertaken both for unmitigated and mitigated piling. Three different types of mitigation techniques were employed. The acceleration zero-to-peak values and the acceleration exposure levels were determined. The results show that inferred mitigation techniques reduce the levels significantly as well as decreases the power content of higher frequencies. These results suggest that mitigation has an effect and will reduce the effect ranges of impact on marine species.

Impact of underwater noise on the growth, physiology and behavior of Micropterus salmoides in industrial recirculating aquaculture systems

The operation of the equipment in industrial recirculating aquaculture systems (RAS) affects the underwater soundscape of aquaculture tanks where fishes live. This study evaluated the influence of commercial industrial RAS noise on the growth, physiology, and behavior of juvenile largemouth bass (Micropterus salmoides). In this study, two experimental groups, the RAS noise group (115 dB re 1 μPa RMS) and the ambient group (69 dB re 1 μPa RMS), were studied. The water quality and feeding regime for each group were kept the same during the 60-day experiment. Results showed that there was no significant difference in the average daily feed intake of the fish between the two treatments, while the rate of weight gain of the ambient group (755.27 ± 65.62%) was significantly higher than that of the noise group (337.66 ± 88.01%). In addition, the RAS environmental noise also had an adverse effect on the anti-oxidation and immune systems of the fish based on results of analysis of blood, liver, and intestinal samples. Moreover, environmental noise affected the swimming behavior of the fish school. The mean angle and distance between the focal fish and its nearest neighbor fish in RAS noise group were 33.3° and 92.1 mm, respectively, which were larger than those of the ambient group with 24.4° and 89.5 mm, respectively. From the above results, RAS noise did influence the welfare of largemouth bass, and the soundscape in RAS hence should be managed in real production.

Calibration methods and facilities for vector receivers using a laser Doppler vibrometer in the frequency range 20 Hz to 10 kHz

Calibration methods and facilities have been employed to directly obtain sensitivities of an underwater acoustic vector receiver using two methods based on laser Doppler vibrometry. The vector receiver was first calibrated in a standing wave tube over the frequency range 20 Hz to 2 kHz, where the oscillatory velocity of the water-air interface was measured to determine the sound particle velocity at the position of vector receiver based on waveguide theory. In the frequency range 2.5-10 kHz, the vector receiver was calibrated in an anechoic vessel with dimensions of 1.2 m diameter × 1.8 m length using wideband signals, with a laser Doppler vibrometer used to detect the oscillatory motion of a plastic pellicle, which was sufficiently thin to follow the acoustic particle motion. The uncertainties of the calibration using the optical method were estimated to be 0.7-0.8 dB at 95% confidence interval. The calibration results were compared with those obtained using a reciprocity method in a 50 m × 15 m × 10 m water tank and using a comparison method in a standing wave tube, and the largest deviation did not exceed 1.0 dB over the frequency range 20 Hz to 10 kHz.

Substrate vibrations and their potential effects upon fishes and invertebrates

This paper reviews the nature of substrate vibration within aquatic environments where seismic interface waves may travel along the surface of the substrate, generating high levels of particle motion. There are, however, few data on the ambient levels of particle motion close to the seabed and within the substrates of lakes and rivers. Nor is there information on the levels and the characteristics of the particle motion generated by anthropogenic sources in and on the substrate, which may have major effects upon fishes and invertebrates, all of which primarily detect particle motion. We therefore consider how to monitor substrate vibration and describe the information gained from modeling it. Unlike most acoustic modeling, we treat the substrate as a solid. Furthermore, we use a model where the substrate stiffness increases with depth but makes use of a wave that propagates with little or no dispersion. This shows the presence of higher levels of particle motion than those predicted from the acoustic pressures, and we consider the possible effects of substrate vibration upon fishes and invertebrates. We suggest that research is needed to examine the actual nature of substrate vibration and its effects upon aquatic animals.

How could operational underwater sound from future offshore wind turbines impact marine life?

Offshore wind farms are part of the transition to a sustainable energy supply and both the total numbers and size of wind turbines are rapidly increasing. While the impact of underwater sound related to construction work has been in the focus of research and regulation, few data exist on the potential impact of underwater sound from operational wind farms. Here, we reviewed published sound levels of underwater sound from operational wind farms and found an increase with size of wind turbines expressed in terms of their nominal power. This trend was identified in both broadband and turbine-specific spectral band sound pressure levels (SPLs). For a nominal power of 10 MW, the trends in broadband SPLs and turbine-specific spectral band SPLs yielded source levels of 170 and 177 dB re 1 μPa m, respectively. The shift from using gear boxes to direct drive technology is expected to reduce the sound level by 10 dB. Using the National Oceanic Atmospheric Administration criterion for behavioral disruption for continuous noise (i.e., level B), a single 10 MW direct drive turbine is expected to cause behavioral response in marine mammals up to 1.4 km distance from the turbine, compared to 6.3 km for a turbine with gear box.

How loud is the underwater noise from operating offshore wind turbines?

Offshore wind turbines are increasingly abundant sources of underwater low frequency noise. This increase raises concern for the cumulative contribution of wind farms to the underwater soundscape and possible impact on marine ecosystems. Here, available measurements of underwater noise from different wind turbines during operation are reviewed to show that source levels are at least 10-20 dB lower than ship noise in the same frequency range. The most important factor explaining the measured sound pressure levels from wind turbines is distance to the turbines with smaller effects of wind speed and turbine size. A simple multi-turbine model demonstrates that cumulative noise levels could be elevated up to a few kilometres from a wind farm under very low ambient noise conditions. In contrast, the noise is well below ambient levels unless it is very close to the individual turbines in locations with high ambient noise from shipping or high wind speeds. The rapid increase in the number and size of offshore wind farms means that the cumulative contribution from the many turbines may be considerable and should be included in assessments for maritime spatial planning purposes as well and environmental impact assessments of individual projects.

Ontogenetic variation in the auditory sensitivity of black sea bass (Centropristis striata) and the implications of anthropogenic sound on behavior and communication

Black sea bass (Centropristis striata) is an important fish species in both commercial and recreational fisheries of southern New England and the mid-Atlantic Bight. Due to the intense urbanization of these waters, this species is subject to a wide range of anthropogenic noise pollution. Concerns that C. striata are negatively affected by pile driving and construction noise predominate in areas earmarked for energy development. However, as yet, the hearing range of C. striata is unknown, making it hard to evaluate potential risks. This study is a first step in understanding the effects of anthropogenic noise on C. striata by determining the auditory detection bandwidth and thresholds of this species using auditory evoked potentials, creating pressure and acceleration audiograms. These physiological tests were conducted on wild-caught C. striata in three size/age categories. Results showed that juvenile C. striata had the significantly lowest thresholds, with auditory sensitivity decreasing in the larger size classes. Furthermore, C.striata has fairly sensitive sound detection relative to other related species. Preliminary investigations into the mechanisms of their sound detection ability were undertaken with gross dissections and an opportunistic micro-computed tomography image to address the auditory structures including otoliths and swim bladder morphology. Crucially, the auditory detection bandwidth of C. striata, and their most sensitive frequencies, directly overlap with high-amplitude anthropogenic noise pollution such as shipping and underwater construction.

Particle motion measurements near a rocky shore off Cabo Frio Island

This paper describes the lessons learned from the experiment BIOCOM'19 carried out in January 2019, in a shallow water bay off the island of Cabo Frio (RJ, Brazil). A dual accelerometer vector sensor hydrophone was deployed for two days, near a rocky shore covered with a significant benthic fauna. The results show that the frequency band above approximately 1.5 kHz is mostly associated with invertebrate biological noise and that the acoustic and the particle motion fields have a similar behavior, following the usual dawn-dusk activity pattern, and a coherent directivity content. At low frequencies, below ∼300 Hz, the acoustic pressure and the particle acceleration fields have significantly different spectral content along time. Many of these differences are due to anthropogenic noise sources related with nearby boating activity, while during quiet periods, they may be attributed to the biological activity from the rocky shore.

Effects of sound exposure from a seismic airgun on heart rate, acceleration and depth use in free-swimming Atlantic cod and saithe

Airguns used for offshore seismic exploration by the oil and gas industry contribute to globally increasing anthropogenic noise levels in the marine environment. There is concern that the omnidirectional, high intensity sound pulses created by airguns may alter fish physiology and behaviour. A controlled short-term field experiment was performed to investigate the effects of sound exposure from a seismic airgun on the physiology and behaviour of two socioeconomically and ecologically important marine fishes: the Atlantic cod (Gadus morhua) and saithe (Pollachius virens). Biologgers recording heart rate and body temperature and acoustic transmitters recording locomotory activity (i.e. acceleration) and depth were used to monitor free-swimming individuals during experimental sound exposures (18-60 dB above ambient). Fish were held in a large sea cage (50 m diameter; 25 m depth) and exposed to sound exposure trials over a 3-day period. Concurrently, the behaviour of untagged cod and saithe was monitored using video recording. The cod exhibited reduced heart rate (bradycardia) in response to the particle motion component of the sound from the airgun, indicative of an initial flight response. No behavioural startle response to the airgun was observed; both cod and saithe changed both swimming depth and horizontal position more frequently during sound production. The saithe became more dispersed in response to the elevated sound levels. The fish seemed to habituate both physiologically and behaviourally with repeated exposure. In conclusion, the sound exposures induced over the time frames used in this study appear unlikely to be associated with long-term alterations in physiology or behaviour. However, additional research is needed to fully understand the ecological consequences of airgun use in marine ecosystems.

Observation and comparison of tower vibration and underwater noise from offshore operational wind turbines in the East China Sea Bridge of Shanghai

Underwater operational turbine noise emitted by China's first offshore wind farm in the East China Sea Bridge of Shanghai was measured and analyzed in this study. Two sensors were used in the measurement: a hydrophone recording the underwater sound and an accelerometer placed in the turbine tower detecting the tower vibrations. Measurements were performed at two different types of wind turbines: a Sinovel 3 MW SL3000 turbine and a Shanghai Electric 3.6 MW W3600 turbine. The two turbines show similar tower vibration characteristics, characterized by a number of tonal components, mainly in the low-frequency domain (30-500 Hz). The peak vibration frequencies changed with the wind speed until the turbine approached its nominal power rating. Spectral analysis of the underwater acoustic data showed that the amplitude spectra had a strong correlation with the spectra of the turbine vibration intensity level, indicating that the measured underwater noise was generated by the tower mechanical vibration.

Underwater operational noise level emitted by a tidal current turbine and its potential impact on marine fauna

Marine renewable energy development raised concerns over the impact of underwater noise. Here we assess the acoustic impacts of an operating tidal current turbine (Paimpol-Bréhat site, France) on marine fauna. Its source level (SL) has been measured in situ using 19 drifting transects at distances between 100 m to 2400 m from the turbine. SL ranged from 118 to 152 dB re1 μPa@1 m in third-octave bands at frequencies between 40 and 8192 Hz. It is comparable to the SL of a 19 m boat travelling at 10kt speed. This SL was used to estimate the impact of this noise type based on acoustic propagation simulations. The acoustic footprint of the device corresponds to a 1.5 km radius disk. Our results show that within this area of greatest potential impact, physiological injury of the hearing apparatus of invertebrates, fishes and marine mammals is improbable. Behavioral disturbance may occur up to 1 km around the device for harbor porpoises only. This is of little concern for a single turbine. However, greater concern on turbine noise impact, particularly on behavioral reactions has to be granted for a farm with up to 100 turbine. The lack of consolidated knowledge on behavioral disturbances identifies the needs for specific research programs.

The importance of particle motion to fishes and invertebrates

This paper considers the importance of particle motion to fishes and invertebrates and the steps that need to be taken to improve knowledge of its effects. It is aimed at scientists investigating the impacts of sounds on fishes and invertebrates but it is also relevant to regulators, those preparing environmental impact assessments, and to industries creating underwater sounds. The overall aim of this paper is to ensure that proper attention is paid to particle motion as a stimulus when evaluating the effects of sound upon aquatic life. Directions are suggested for future research and planning that, if implemented, will provide a better scientific basis for dealing with the impact of underwater sounds on marine ecosystems and for regulating those human activities that generate such sounds. The paper includes background material on underwater acoustics, focusing on particle motion; the importance of particle motion to fishes and invertebrates; and sound propagation through both water and the substrate. Consideration is then given to the data gaps that must be filled in order to better understand the interactions between particle motion and aquatic animals. Finally, suggestions are provided on how to increase the understanding of particle motion and its relevance to aquatic animals.

The sense of hearing in the Pacific oyster, Magallana gigas

There is an increasing concern that anthropogenic noise could have a significant impact on the marine environment, but there is still insufficient data for most invertebrates. What do they perceive? We investigated this question in oysters Magallana gigas (Crassostrea gigas) using pure tone exposures, accelerometer fixed on the oyster shell and hydrophone in the water column. Groups of 16 oysters were exposed to quantifiable waterborne sinusoidal sounds in the range of 10 Hz to 20 kHz at various acoustic energies. The experiment was conducted in running seawater using an experimental flume equipped with suspended loudspeakers. The sensitivity of the oysters was measured by recording their valve movements by high-frequency noninvasive valvometry. The tests were 3 min tone exposures including a 70 sec fade-in period. Three endpoints were analysed: the ratio of responding individuals in the group, the resulting changes of valve opening amplitude and the response latency. At high enough acoustic energy, oysters transiently closed their valves in response to frequencies in the range of 10 to <1000 Hz, with maximum sensitivity from 10 to 200 Hz. The minimum acoustic energy required to elicit a response was 0.02 m∙s^-2 at 122 dBrms re 1 μPa for frequencies ranging from 10 to 80 Hz. As a partial valve closure cannot be differentiated from a nociceptive response, it is very likely that oysters detect sounds at lower acoustic energy. The mechanism involved in sound detection and the ecological consequences are discussed.

Good or bad vibrations? Impacts of anthropogenic vibration on the marine epibenthos

Anthropogenic activities directly contacting the seabed, such as drilling and pile-driving, produce a significant vibration likely to impact benthic invertebrates. As with terrestrial organisms, vibration may be used by marine species for the detection of biotic and abiotic cues, yet the significance of this and the sensitivities to vibration are previously undocumented for many marine species. Exposure to additional vibration may elicit behavioral or physiological change, or even physical damage at high amplitudes or particular frequencies, although this is poorly studied in underwater noise research. Here we review studies regarding the sensitivities and responses of marine invertebrates to substrate-borne vibration. This includes information related to vibrations produced by those construction activities directly impacting the seabed, such as pile-driving. This shows the extent to which species are able to detect vibration and respond to anthropogenically-produced vibrations, although the short and long-term implications of this are not known. As such it is especially important that the sensitivities of these species are further understood, given that noise and energy-generating human impacts on the marine environment are only likely to increase and that there are now legal instruments requiring such effects to be monitored and controlled.

Offshore exposure experiments on cuttlefish indicate received sound pressure and particle motion levels associated with acoustic trauma

Recent findings on cephalopods in laboratory conditions showed that exposure to artificial noise had a direct consequence on the statocyst, sensory organs, which are responsible for their equilibrium and movements in the water column. The question remained about the contribution of the consequent near-field particle motion influence from the tank walls, to the triggering of the trauma. Offshore noise controlled exposure experiments (CEE) on common cuttlefish (Sepia officinalis), were conducted at three different depths and distances from the source and particle motion and sound pressure measurements were performed at each location. Scanning electron microscopy (SEM) revealed injuries in statocysts, which severity was quantified and found to be proportional to the distance to the transducer. These findings are the first evidence of cephalopods sensitivity to anthropogenic noise sources in their natural habitat. From the measured received power spectrum of the sweep, it was possible to determine that the animals were exposed at levels ranging from 139 to 142 dB re 1 μPa2 and from 139 to 141 dB re 1 μPa2, at 1/3 octave bands centred at 315 Hz and 400 Hz, respectively. These results could therefore be considered a coherent threshold estimation of noise levels that can trigger acoustic trauma in cephalopods.

Measurement and characterisation of radiated underwater sound from a 3.6 MW monopile wind turbine

This paper describes underwater sound pressure measurements obtained in close proximity (∼50 m) to two individual wind turbines, over a 21-day period, capturing the full range of turbine operating conditions. The sound radiated into the water was characterised by a number of tonal components, which are thought to primarily originate from the gearbox for the bandwidth measured. The main signal associated with the turbine operation had a mean-square sound pressure spectral density level which peaked at 126 dB re 1 μPa2 Hz-1 at 162 Hz. Other tonal components were also present, notably at frequencies between about 20 and 330 Hz, albeit at lower amplitudes. The measured sound characteristics, both in terms of frequency and amplitude, were shown to vary with wind speed. The sound pressure level increased with wind speed up to an average value of 128 dB re 1 μPa at a wind speed of about 10 ms-1, and then showed a general decrease. Overall, differences in the mean-square sound pressure spectral density level of over 20 dB were observed across the operational envelope of the turbine.