The importance of underwater sounds to gadoid fishes

Soundscape and fish passive acoustic monitoring around a North Sea gas-production platform in the Dogger Bank

This study provides temporo-spatial characterisation of the underwater soundscape in proximity of a relatively newly installed offshore gas-production platform in the North Sea's Dogger Bank Special Area of Conservation, recorded by Static Acoustic Monitoring at different distances from the wellhead (70 m, 5 Km and 10 km). Long-Term Spectrogram Analysis and percentile Power Spectral Densities demonstrated strong acoustic similarity between sites; no biophonic acoustic-mass phenomena were present. All locations were characterized by Underwater Radiated Noise, concentrated < 2 kHz, which dominated the soundscape. Fish acoustic community analysis was performed to explore occurrence, richness, abundance, diel, and seasonal patterns of putative fish sounds. Principal Component Analysis was used to infer potential sound-emitting species, and was performed on North Sea fish sounds downloaded from the Global Inventory of known fish sounds (https://fishsounds.net/), analyzed for the same acoustic features used to characterize fish sounds recorded during this study. The fish acoustic community was characterized by low levels of diversity (acoustic richness ranging from 1 to 2) and abundance (never above 2 sounds min-1). The fish sound type 'Pulse Series' (PS), emitted at the 70 m and at the 5 km station in low abundance in September from ca. 19:00 to 23:00, was characterized by acoustic features with the closest linear combination to those typifying sounds emitted by Eutrigla gurnardus. The fish sound type 'Low-frequency Down-Sweep' (LF-DS) was recorded at all stations and was characterized by acoustic features with the closest linear combination to those typifying grunts emitted by Gadus morhua. This study represents the first application of fish acoustic community analysis in the context of environmental management of an operational offshore gas production platform.

Rapid predator-prey balance shift follows critical-population-density transmission between cod (Gadus morhua) and capelin (Mallotus villosus)

Sensing limitations have impeded knowledge about how individual predator-prey interactions build to organized multi-species group behaviour across an ecosystem. Population densities of overlapping interacting oceanic fish predator and prey species, however, can be instantaneously distinguished and quantified from roughly the elemental individual to spatial scales spanning thousands of square kilometres by wide-area multispectral underwater-acoustic sensing, as shown here. This enables fundamental mechanisms behind large-scale ordered predator-prey interactions to be investigated. Critical population densities that transition random individual behaviour to ordered group behaviour are found to rapidly propagate to form vast adversarial prey and predator shoals of capelin and surrounding cod in the Barents Sea Arctic ecosystem for these keystone species. This leads to a sudden major shift in predator-prey balance. Only a small change in local behaviour triggers the shift due to an unstable equilibrium. Such unstable equilibria and associated balance shifts at predation hotspots are often overlooked as blind spots in present ocean ecosystem monitoring and assessment due to use of highly undersampled spatio-temporal sampling methods.

Natural and shipping underwater sound distribution in the Northern Adriatic Sea basin and possible application on target areas

The underwater sound distribution generated by natural sources, shipping and trawling activities has been computed by the Quonops© modelling webservice for the Northern Adriatic Sea (NAS) during 2020, a year characterized by the COVID-19 lockdown restrictions. Modelling has been calibrated by using a year-long time series of field measurements covering the domain of interest. Sound levels (50th percentile) ranged between 75 and 90 dB re 1μPa for all the considered frequencies (63 Hz, 125 Hz, 250 Hz third octave bands). Noisier NAS areas match with the shipping lanes and the distribution of trawling activity. Pressure sound indices based on masking effect were computed for two Ecologically/Biologically Significant Marine Areas (EBSA) located in the NAS. Results indicated a significant contribution of vessel and fishery-generated noise to the local soundscape and provide a basis for addressing NAS underwater noise pollution, with special reference to the Marine Spatial Planning approach.

Continuous sound from a marine vibrator causes behavioural responses of free-ranging, spawning Atlantic cod (Gadus morhua)

Marine vibrators are a new technology being developed for seismic surveys. These devices can transmit continuous instead of impulsive sound and operate over a narrower frequency band and at lower peak pressure than airguns, which is assumed to reduce their environmental impacts. We exposed spawning Atlantic cod (Gadus morhua) to sound produced by a prototype, but full-scale, marine vibrator, and monitored behavioural responses of tagged cod using acoustic telemetry. Fish were exposed to 10 × 3 h continuous sound treatments over a 4-day period using a randomised-block design. Sound exposure levels were comparable to airgun exposure experiments conducted previously with the same set-up ranging from ∼115 to 145 dB re 1 μPa2s during exposure. Telemetry data were used to assess 1) whether marine vibrator exposure displaced cod from the spawning ground, through estimation of residence and survival probabilities, and 2) fine-scale behavioural responses within the test site, namely swimming depth, activity levels, displacement, and home ranges. Forty-two spawning cod were tagged prior to the exposure, with 22 present during the exposure. All 22 tags were equipped with pressure sensors and ten of these additionally with accelerometers. While no premature departure from the spawning site was observed, cod reacted to the exposure by decreasing their activity levels (by up to 50%, SE = 7%) and increasing their swimming depth (by up to 2.5 m, SE = 1.0 m) within the test site during the exposure period. These behavioural responses varied by sex and time of day. Cod reactions to a marine vibrator may be more pronounced than reactions to airguns, possibly because continuous sound is more disturbing to fish than intermittent sound at the same exposure levels. However, given sample size limitations of the present study, further studies with continuous sound are necessary to fully understand its impact and biological significance.

Sound and sturgeon: Bioacoustics and anthropogenic sounda)

Sturgeons are basal bony fishes, most species of which are considered threatened and/or endangered. Like all fishes, sturgeons use hearing to learn about their environment and perhaps communicate with conspecifics, as in mating. Thus, anything that impacts the ability of sturgeon to hear biologically important sounds could impact fitness and survival of individuals and populations. There is growing concern that the sounds produced by human activities (anthropogenic sound), such as from shipping, commercial barge navigation on rivers, offshore windfarms, and oil and gas exploration, could impact hearing by aquatic organisms. Thus, it is critical to understand how sturgeon hear, what they hear, and how they use sound. Such data are needed to set regulatory criteria for anthropogenic sound to protect these animals. However, very little is known about sturgeon behavioral responses to sound and their use of sound. To help understand the issues related to sturgeon and anthropogenic sound, this review first examines what is known about sturgeon bioacoustics. It then considers the potential effects of anthropogenic sound on sturgeon and, finally identifies areas of research that could substantially improve knowledge of sturgeon bioacoustics and effects of anthropogenic sound. Filling these gaps will help regulators establish appropriate protection for sturgeon.

Atlantic cod (Gadus morhua) larvae are attracted by low-frequency noise simulating that of operating offshore wind farms

The number and size of offshore wind (OW) turbines is increasing rapidly. OW turbines produce continuous, low-frequency noise that could impact marine fish dispersing/migrating through the facilities. Any such impact would be relevant for larval stages, which have limited possibility to swim away from OW facilities. If directional movement of fish larvae at sea is impacted by low-frequency continuous sound is unknown. We observe the behavior of Atlantic cod larvae (N = 89) in response to low-frequency sound while they are drifting in a Norwegian fjord inside transparent drifting chambers. We transmit 100 Hz continuous sound in the fjord, in the intensity range of OW turbines' operational noise, and measure the sound pressure and 3-D particle motion. Half of the larvae (N = 45) are exposed to low-frequency (100 Hz) continuous sound, while the other half (N = 44) are observed under the same conditions but without the sound. Exposure does not affect the routine and maximum swimming speeds or the turning behavior of the larvae. Control larvae orient to the northwest. In contrast, exposed larvae orient towards the source of low-frequency sound and particle motion. This provides a basis to assess how OW might impact dispersal in this species.

The importance of sound to the Atlantic cod, Gadus morhua, and the Atlantic haddock, Melanogrammus aeglefinus

The gadoid fishes, including the Atlantic cod and haddock, are currently being exploited close to their safe biological limits, requiring restrictions upon the human activities that may harm them. This has prompted interest in the biology of such fishes. Studies of the cod and haddock have shown highly complex behavior, involving prolonged and energetic visual and acoustic displays. Different sounds are produced in different behavioral contexts and are emitted almost continuously by cod and haddock, especially throughout the spawning season (February to May). The distinctive characteristics of these sounds make it possible to locate spawning cod and haddock at their marine spawning grounds. Human activities in these areas may affect their spawning adversely and have deleterious effects upon their stocks. Man-made sounds in water do have an adverse effect upon cod and haddock, and other fishes. Listening for the cod and haddock sounds provides a reliable, non-invasive technique for detecting their locations, and especially their spawning areas, and enables them to be protected well.

A Gulf in lockdown: How an enforced ban on recreational vessels increased dolphin and fish communication ranges

From midnight of 26 March 2020, New Zealand became one of the first countries to enter a strict lockdown to combat the spread of COVID-19. The lockdown banned all non-essential services and travel both on land and sea. Overnight, the country's busiest coastal waterway, the Hauraki Gulf Marine Park, became devoid of almost all recreational and non-essential commercial vessels. An almost instant change in the marine soundscape ensued, with ambient sound levels in busy channels dropping nearly threefold the first 12 h. This sudden drop led fish and dolphins to experience an immediate increase in their communication ranges by up to an estimated 65%. Very low vessel activity during the lockdown (indicated by the presence of vessel noise over the day) revealed new insights into cumulative noise effects from vessels on auditory masking. For example, at sites nearer Auckland City, communication ranges increased approximately 18 m (22%) or 50 m (11%) for every 10% decrease in vessel activity for fish and dolphins, respectively. However, further from the city and in deeper water, these communication ranges were increased by approximately 13 m (31%) or 510 m (20%). These new data demonstrate how noise from small vessels can impact underwater soundscapes and how marine animals will have to adapt to ever-growing noise pollution.

Sound detection by Atlantic cod: An overview

The Atlantic cod (Gadus morhua) is among the commercially most important fish species in the world. Since sound plays such an important role in the lives of Atlantic cod and its related species, understanding of their bioacoustics is of great importance. Moreover, since cod are amenable to studies of hearing, especially in open bodies of water, they have the potential to become a "model species" for investigations of fish hearing. To serve as the basis for future studies, and to bring together what is now known about cod hearing, this paper reviews the literature to date. While there is some discussion of other species in the paper, the focus is upon what is already known about cod hearing, and what now needs to be known. An additional focus is on what knowledge of cod hearing tells about hearing in fishes in general.

Spatio-temporal distribution and acoustic characterization of haddock (Melanogrammus aeglefinus, Gadidae) calls in the Arctic fjord Kongsfjorden (Svalbard Islands)

In this study we analysed the acoustic properties and presence of haddock calls in the Arctic fjord Kongsfjorden (79° N–12° E, Svalbard Islands, Norway) in one year. Data were collected with three autonomous acoustic recorders located in the inner, middle, and outer parts of the fjord. The fjord is characterized by a gradient of oceanographic conditions from the inner to the outer part, reflecting changes from Arctic to Atlantic waters. Haddock sounds were more abundant in the outer fjord than in the middle fjord, whereas they were absent at the inner site. Mainly at the open-water site, the call abundance exhibited strong periodicity and a correlation with the cycles of neap tide (15 days) in August, with a clear diel cycle (24 h) in September and October. This result suggests that in this extreme environment with 24 h of light during summer, haddock regulate their acoustic activity according to the main available oscillating external physical driver, such as tide during the polar summer, while when the alternation of light/dark starts, they shift the periodicity of their calls to a diel cycle. Calls were recorded outside the spawning period (from July to October), and their characteristics indicated non-reproductive communicative contests. By using a detailed sound analysis based on previous laboratory studies for the first time, we suggest that the monitored population contains mainly juveniles (44% compared to 41% females and only approximately 15% mature males), showing the predominance of females in the middle fjord and juveniles at the open-water site.

Introduction to the special issue on the effects of sound on aquatic life

The effects of anthropogenic (man-made) underwater sound on aquatic life have become an important environmental issue. One of the focal ways to present and to share knowledge on the topic has been the international conference on The Effects of Noise on Aquatic Life ("Aquatic Noise"). The conferences have brought together people from diverse interests and backgrounds to share information and ideas directed at understanding and solving the challenges of the potential effects of sound on aquatic life. The papers published here and in a related special issue of Proceedings of Meetings on Acoustics present a good overview of the many topics and ideas covered at the meeting. Indeed, the growth in studies on anthropogenic sound since the first meeting in 2007 reflects the increasing use of oceans, lakes, rivers, and other waterways by humans. However, there are still very substantial knowledge gaps about the effects of sound on all aquatic animals, and these gaps lead to there being a substantial need for a better understanding of the sounds produced by various sources and how these sounds may affect animals.

Assessing auditory masking for management of underwater anthropogenic noise

Masking is often assessed by quantifying changes, due to increasing noise, to an animal's communication or listening range. While the methods used to measure communication or listening ranges are functionally similar if used for vocalizations, they differ in their approaches: communication range is focused on the sender's call, while the listening range is centered on the listener's ability to perceive any signal. How these two methods differ in their use and output is important for management recommendations. Therefore it was investigated how these two methods may alter the conclusions of masking assessments based on Atlantic cod calls in the presence of a commercial air gun array. The two methods diverged with increasing distance from the masking noise source with maximum effects lasting longer between air gun pulses in terms of communication range than listening range. Reductions in the cod's communication ranges were sensitive to fluctuations in the call's source level. That instability was not observed for the listening range. Overall, changes to the cod's communication range were more conservative but very sensitive to the call source level. A high level of confidence in the call is therefore required, while confidence in the receiver's audiogram and soundscape is required for the listening range method.

Fish biophony in a Mediterranean submarine canyon

Although several bioacoustics investigations have shed light on the acoustic communication of Mediterranean fish species, the occurrence of fish sounds has never been reported below -40 m depth. This study assessed the occurrence of fish sounds at greater depths by monitoring the soundscape of a Mediterranean submarine canyon (Calvi, France) thanks to a combination of Static Acoustic Monitoring (three stations, from -125 to -150 m depth, 3 km from coastline) and of hydrophone-integrated gliders (Mobile Acoustic Monitoring; from -60 to -900 m depth, 3-6 km from coastline). Biological sounds were detected in 38% of the audio files; ten sound types (for a total of more than 9.000 sounds) with characteristics corresponding to those emitted by vocal species, or known as produced by fish activities, were found. For one of these sound types, emitter identity was inferred at the genus level (Ophidion sp.). An increase of from 10 to 15 dB re 1 μPa in sea ambient noise was observed during daytime hours due to boat traffic, potentially implying an important daytime masking effect. This study shows that monitoring the underwater soundscape of Mediterranean submarine canyons can provide holistic information needed to better understand the state and the dynamics of these heterogeneous, highly diverse environments.