Acoustic Pressure, Particle Motion, and Induced Ground Motion Signals from a Commercial Seismic Survey Array and Potential Implications for Environmental Monitoring

Long-range propagation of airgun-array signals: Comparing numerical simulations and acoustic recordings in the Ionian sea

Marine seismic surveys contribute to acoustic pollution, and the sounds they produce may be audible by marine mammals at several hundred kilometers distance. To evaluate the potential effects of such sounds on fauna and translate them into effective policies and mitigation measures, stakeholders require quantitative estimations of acoustic fields. We compare simulations of airgun-array signals produced during the Upper LIthosphere Ship Subduction Exploration survey in the Ionian Sea with the signals recorded 650 kilometers away at the cabled seabed observatory NEMO-SN1. JASCO's Applied Sciences' Airgun Array Source Model was used to predict the sound levels for two configurations of 18-element airguns, and the signal was then propagated in a realistic environment utilizing JASCO's Full-Waveform Range dependent Acoustic Model from the source to the position of the receiver station. There is a qualitative agreement between the simulated, denoised, and recorded signals of the airgun arrivals. However, the signal simulated at 650 kilometers from the source stretches and shows fewer high-frequency components compared to the received one. Our study quantitatively shows that the peaks produced by a large airgun array during a scientific cruise, at 160-180 Hz are not masked by ambient noise even in busy shipping locations at a distance of 650 km.

Insights into the transcriptomic responses of silver-lipped pearl oysters Pinctada maxima exposed to a simulated large-scale seismic survey

BACKGROUND

The wild stocks of Pinctada maxima pearl oysters found off the coast of northern Australia are of critical importance for the sustainability of Australia's pearling industry. Locations inhabited by pearl oysters often have oil and gas reserves in the seafloor below and are therefore potentially subjected to seismic exploration surveys. The present study assessed the impact of a simulated commercial seismic survey on the transcriptome of pearl oysters. Animals were placed at seven distances (-1000, 0, 300, 500, 1000, 2000, and 6000 m) from the first of six operational seismic source sail lines. Vessel control groups were collected before the seismic survey started and exposed groups were collected after completion of six operational seismic sail lines (operated at varying distances over a four-day period). Samples from these groups were taken immediately and at 1, 3, and 6 months post-exposure. RNA-seq was used to identify candidate genes and pathways impacted by the seismic noise in pearl oyster mantle tissues. The quantified transcripts were compared using DESeq2 and pathway enrichment analysis was conducted using KEGG pathway, identifying differentially expressed genes and pathways associated with the seismic activity.

RESULTS

The study revealed the highest gene expression and pathway dysregulation after four days of exposure and a month post-exposure. However, this dysregulation diminished after three months, with only oysters at -1000 and 0 m displaying differential gene expression and pathway disruption six months post-exposure. Stress-induced responses were evident and impacted energy production, transcription, translation, and protein synthesis.

CONCLUSION

Seismic activity impacted the gene expression and pathways of pearl oysters at distances up to 2000 m from the source after four days of exposure, and at distances up to 1000 m from the source one-month post-exposure. At three- and six-months post-exposure, gene and pathway dysregulations were mostly observed in oysters located closest to the seismic source at 0 and - 1000 m. Overall, our results suggest that oysters successfully activated stress responses to mitigate damage and maintain cellular homeostasis and growth in response to seismic noise exposure.

A large-scale experiment finds no consistent evidence of change in mortality or commercial productivity in silverlip pearl oysters (Pinctada maxima) exposed to a seismic source survey

High-intensity, impulsive sounds are used to locate oil and gas reserves during seismic exploration of the seafloor. The impacts of this noise pollution on the health and mortality of marine invertebrates are not well known, including the silverlip pearl oyster (Pinctada maxima), which comprises one of the world's last remaining significant wildstock pearl oyster fisheries, in northwestern Australia. We exposed ≈11,000 P. maxima to a four-day experimental seismic survey, plus one vessel-control day. After exposure, survival rates were monitored throughout a full two-year production cycle, and the number and quality of pearls produced at harvest were assessed. Oysters from two groups, on one sampling day, exhibited reduced survival and pearl productivity compared to controls, but 14 other groups receiving similar or higher exposure levels did not. We therefore found no conclusive evidence of an impact of the seismic source survey on oyster mortality or pearl production.

Sound sensitivity of the giant scallop (Placopecten magelanicus) is life stage, intensity, and frequency dependent

There is increasing concern that anthropogenic sounds have a significant impact on marine animals, but there remains insufficient data on sound sensitivities for most invertebrates, despite their ecological and economic importance. We quantified auditory thresholds (in particle acceleration levels) and bandwidth of the giant scallop (Placopecten magellanicus) and subsequently sought to discern sensitivity among two different life stages: juveniles (1 yr olds) and subadults (3 yr olds). We also leveraged a novel valvometry technique to quantify the amplitude of scallop valve gape reductions when exposed to different sound amplitudes and frequencies. Behavioral responses were obtained for lower frequencies below 500 Hz, with best sensitivity at 100 Hz. There were significant differences between the auditory thresholds of juveniles and subadults, with juveniles being more sensitive, suggesting ontogenetic differences in hearing sensitivity. Scallops showed intensity and frequency dependent responses to sounds, with higher valve closures to lower frequencies and higher sound levels. To our knowledge, these are the first data highlighting life stage, intensity, and frequency responses to sound in a marine benthic invertebrate. These results demonstrate clear sound sensitivity and underscore that the potential impacts of anthropogenic sound in valuable ecological resources, such as scallops, may be dependent on sound characteristics.

The impact of seismic survey exposure on the righting reflex and moult cycle of Southern Rock Lobster (Jasus edwardsii) puerulus larvae and juveniles

Anthropogenic aquatic noise is recognised as an environmental pollutant with the potential to negatively affect marine organisms. Seismic surveys, used to explore subseafloor oil reserves, are a common source of aquatic noise that have garnered attention due to their intense low frequency inputs and their frequent spatial overlap with coastal fisheries. Commercially important Southern Rock Lobster (Jasus edwardsii) adults have previously shown sensitivity to signals from a single seismic air gun. Here, the sensitivity of J. edwardsii juveniles and puerulus to the signals of a full-scale seismic survey were evaluated to determine if early developmental stages were affected similarly to adults, and the range of impact. To quantify impact, lobster mortality rates, dorsoventral righting reflex and progression through moult cycle were evaluated following exposure. Exposure did not result in mortality in either developmental stage, however, air gun signals caused righting impairment to at least 500 m in lobsters sampled immediately following exposure, as had previously been reported in adults with corresponding sensory system damage following exposure. Impairment resulting from close range (0 m) exposure appeared to be persistent, as previously reported in adults, whereas juveniles exposed at a more distant range (500 m) showed recovery, indicating that exposure at a range of 500 m may not cause lasting impairment to righting. Intermoult duration was (time between moults) significantly increased in juveniles exposed at 0 m from the source, indicating the potential for slowed development, growth, and physiological stress. These results demonstrate that exposure to seismic air gun signals have the potential to negatively impact early life history stages of Southern Rock Lobsters. The similarity of both the impacts and the sound exposure levels observed here compared to previous exposure using a single air gun offer validation for the approach, which opens the potential for accessible field-based experimental work into the impact of seismic surveys on marine invertebrates.

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.

Sounding the Call for a Global Library of Underwater Biological Sounds

Aquatic environments encompass the world’s most extensive habitats, rich with sounds produced by a diversity of animals. Passive acoustic monitoring (PAM) is an increasingly accessible remote sensing technology that uses hydrophones to listen to the underwater world and represents an unprecedented, non-invasive method to monitor underwater environments. This information can assist in the delineation of biologically important areas via detection of sound-producing species or characterization of ecosystem type and condition, inferred from the acoustic properties of the local soundscape. At a time when worldwide biodiversity is in significant decline and underwater soundscapes are being altered as a result of anthropogenic impacts, there is a need to document, quantify, and understand biotic sound sources–potentially before they disappear. A significant step toward these goals is the development of a web-based, open-access platform that provides: (1) a reference library of known and unknown biological sound sources (by integrating and expanding existing libraries around the world); (2) a data repository portal for annotated and unannotated audio recordings of single sources and of soundscapes; (3) a training platform for artificial intelligence algorithms for signal detection and classification; and (4) a citizen science-based application for public users. Although individually, these resources are often met on regional and taxa-specific scales, many are not sustained and, collectively, an enduring global database with an integrated platform has not been realized. We discuss the benefits such a program can provide, previous calls for global data-sharing and reference libraries, and the challenges that need to be overcome to bring together bio- and ecoacousticians, bioinformaticians, propagation experts, web engineers, and signal processing specialists (e.g., artificial intelligence) with the necessary support and funding to build a sustainable and scalable platform that could address the needs of all contributors and stakeholders into the future.

A Review and Meta-Analysis of Underwater Noise Radiated by Small (<25 m Length) Vessels

Managing the impacts of vessel noise on marine fauna requires identifying vessel numbers, movement, behaviour, and acoustic signatures. However, coastal and inland waters are predominantly used by ‘small’ (<25 m-long) vessels, for which there is a paucity of data on acoustic output. We reviewed published literature to construct a dataset (1719 datapoints) of broadband source levels (SLs) from 17 studies, for 11 ‘Vessel Types’. After consolidating recordings that had associated information on factors that may affect SL estimates, data from seven studies remained (1355 datapoints) for statistical modelling. We applied a Generalized Additive Mixed Model to assess factors (six continuous and five categorical predictor variables) contributing to reported SLs for four Vessel Types. Estimated SLs increased through ‘Electric’, ‘Skiff’, ‘Sailing’, ‘Monohull’, ‘RHIB’, ‘Catamaran’, ‘Fishing’, ‘Landing Craft’,’ Tug’, ‘Military’ to ‘Cargo’ Vessel Types, ranging between 130 and 195 dB re 1µPa m across all Vessel Types and >29 dB range within individual Vessel Types. The most parsimonious model (22.7% deviance explained) included ‘Speed’ and ‘Closest Point of Approach’ (CPA) which displayed non-linear, though generally positive, relationships with SL. Similar to large vessels, regulation of speed can reduce SLs and vessel noise impacts (with consideration for additional exposure time from travelling at slower speeds). However, the relationship between speed and SLs in planing hull and semi-displacement vessels can be non-linear. The effect of CPA on estimated SL is likely a combination of propagation losses in the shallow study locations, often-neglected surface interactions, different methodologies, and that the louder Vessel Types were often recorded at greater CPAs. Significant effort is still required to fully understand SL variability, however, the International Standards Organisation’s highest reporting criteria for SLs requires water depths that often only occur offshore, beyond the safe operating range of small vessels. Additionally, accurate determination of monopole SLs in shallow water is complicated, requiring significant geophysical information along the signal path. We suggest the development of appropriate shallow-water criteria to complete these measurements using affected SLs and a comprehensive study including comparable deep- and shallow-water measures.

A large-scale experiment finds no evidence that a seismic survey impacts a demersal fish fauna

Seismic surveys are used to locate deposits of oil and gas in seabeds throughout the world’s oceans. There are conflicting views on the impact of these surveys on fish fauna and whether they harm commercial catches. To resolve this issue, we conducted an experimental seismic survey and monitored the composition, abundance, behavior, and movement of an assemblage of commercially important demersal fishes on a shelf habitat using acoustic telemetry and underwater video. We found that the seismic survey did not alter fish abundance or behavior in multiple before-after-control-impact and dose–response experimental frameworks. Our work may allay some of the concerns of stakeholders about the negative impacts of seismic surveys on demersal fishes in tropical shelf environments.

Seismic surveys are used to locate oil and gas reserves below the seabed and can be a major source of noise in marine environments. Their effects on commercial fisheries are a subject of debate, with experimental studies often producing results that are difficult to interpret. We overcame these issues in a large-scale experiment that quantified the impacts of exposure to a commercial seismic source on an assemblage of tropical demersal fishes targeted by commercial fisheries on the North West Shelf of Western Australia. We show that there were no short-term (days) or long-term (months) effects of exposure on the composition, abundance, size structure, behavior, or movement of this fauna. These multiple lines of evidence suggest that seismic surveys have little impact on demersal fishes in this environment.