A brief overview of current approaches for underwater sound analysis and reporting

Zooplankton as a model to study the effects of anthropogenic sounds on aquatic ecosystems

There is a growing interest in the impact of acoustic pollution on aquatic ecosystems. Currently, research has primarily focused on hearing species, particularly fishes and mammals. However, species from lower trophic levels, including many invertebrates, are less studied despite their ecological significance. Among these taxa, studies examining the effects of sound on holozooplankton are extremely rare. This literature review examines the effects of sound on both marine and freshwater zooplankton. It highlights two differences: the few used organisms and the types of sound source. Marine studies focus on the effects of very intense acute sound on copepods, while freshwater studies focus on less intense chronic sound on cladocerans. But, in both, various negative effects are reported. The effects of sound remain largely unknown, although previous studies have shown that zooplankton can detect vibrations using mechanoreceptors. The perception of their environment can be affected by sounds, potentially causing stress. Limited research suggests that sound may affect the physiology, behaviour, and fitness of zooplankton. Following this review, I highlight the potential to use methods from ecology, ecotoxicology, and parasitology to study the effects of sound at the individual level, including changes in physiology, development, survival, and behaviour. Responses to sound, which could alter species interactions and population dynamics, are expected to have larger-scale implications with bottom-up effects, such as changes in food web dynamics and ecosystem functioning. To improve the study of the effect of sound, to better use zooplankton as biological models and as bioindicators, researchers need to better understand how they perceive their acoustic environment. Consequently, an important challenge is the measurement of particle motion to establish useable dose-response relationships and particle motion soundscapes.

Avoidance, confusion or solitude? Modelling how noise pollution affects whale migration

Many baleen whales are renowned for their acoustic communication. Under pristine conditions, this communication can plausibly occur across hundreds of kilometres. Frequent vocalisations may allow a dispersed migrating group to maintain contact, and therefore benefit from improved navigation via the "wisdom of the crowd". Human activities have considerably inflated ocean noise levels. Here we develop a data-driven mathematical model to investigate how ambient noise levels may inhibit whale migration. Mathematical models allow us to simultaneously simulate collective whale migration behaviour, auditory cue detection, and noise propagation. Rising ambient noise levels are hypothesised to influence navigation through three mechanisms: (i) diminished communication space; (ii) reduced ability to hear external sound cues and; (iii) triggering noise avoidance behaviour. Comparing pristine and current soundscapes, we observe navigation impairment that ranges from mild (increased journey time) to extreme (failed navigation). Notably, the three mechanisms induce qualitatively different impacts on migration behaviour. We demonstrate the model's potential predictive power, exploring the extent to which migration may be altered under future shipping and construction scenarios.

First basin scale spatial-temporal characterization of underwater sound in the Mediterranean Sea

Anthropogenic underwater noise is an emergent pollutant. Despite several worldwide monitoring programs, only few data are available for the Mediterranean Sea, one of the global biodiversity hotspots. The results of the first continuous acoustic programme run at a transnational basin scale in the Mediterranean Sea are here presented. Recordings were done from March 2020 to June 2021, including the COVID-19 lockdown, at nine stations in the Northern Adriatic Sea. Spatial-temporal variations of the underwater sound are described, having one third octave band sound pressure levels (SPLs) from 10 Hz to 20 kHz as metrics. Higher and more variable SPLs, mainly related to vessel traffic, were found close to harbours, whereas Natura 2000 stations experienced lower SPLs. Lower values were recorded during the lockdown in five stations. Median yearly SPLs ranged between 64 and 95 as well as 70 and 100 dB re 1 µPa for 63 and 125 Hz bands, respectively. These values are comparable with those previously found in busy shallow EU basins but higher levels are expected during a business-as-usual period. This is a baseline assessment for a highly impacted and environmental valuable area, that needs to be managed in a new sustainable blue growth strategy.

Statistical study on shallow water soundscape variability of Eastern Arabian Sea using noise level metrics

Underwater soundscape that spans a broad frequency band shows variability consistent with contributing noise sources and ocean environment. However, increased anthropogenic activities result in noise proliferation which can harm natural marine habitat. Continuous monitoring of background sound is useful to assess such spatio-temporal variability of soundscape. Standard noise level metrics, for instance, mean (μ), 90th percentiles (90P), standard deviation (σ), and kurtosis (β), are constructed from noise field measured from three coastal stations in Eastern Arabian Sea. These metrics are found to be suitable to describe the soundscape variability with respect to season, frequency, and depth. Mean and 90P are used to compare the seasonal variations while kurtosis metrics are exercised to check the impulsive nature of composite signal. Histogram representation and probability density function (PDF) were utilized to analyze the spectral variation in soundscape with respect to season. Analysis was carried out at 500-ms temporal window in two spectral bands corresponding to traffic and wind noise fields. Seasonal analysis shows that in summer, mean noise level decreases as hydrophone depth increases, while in winter, deeper depths have higher mean value with the presence of seasonal surface duct. This implication of sound speed profile on noise field has also been confirmed using appropriate noise model.

Efforts to advance underwater noise management in Canada: Introduction to the Marine Pollution Bulletin Special Issue

This introduction to a special issue on approaches to managing underwater noise in Canada provides a brief overview of recent efforts to better understand and reduce anthropogenic underwater noise. Recent programs have aimed to increase understanding of anthropogenic noise in the habitats of highly endangered whales and have supported management actions such as vessel slow downs. Technical workshops have advanced the development of quiet ship design and associated technologies. Collaborative research examined noise levels in the St. Lawrence Estuary and the Arctic Ocean. Efforts to better manage noise have gone beyond shipping: enhanced mitigation measures have been put in place for naval exercises near habitats used by southern resident killer whales, while other work has focused on the identification of appropriate metrics for measuring noise. To coordinate and advance these and other efforts, the Government of Canada is developing a national Ocean Noise Strategy.