A decade of underwater noise research in support of the European Marine Strategy Framework Directive.

Underwater noise from human activities is now widely recognised as a threat to marine life. Nevertheless, legislation which directly addresses this source of pollution is lacking. The first (and currently only) example globally is Descriptor 11 of the Marine Strategy Framework Directive (MSFD), adopted by the European Union in 2008, which requires that levels of underwater noise pollution do not adversely affect marine ecosystems. The MSFD has stimulated a concerted research effort across Europe to develop noise monitoring programmes and to conduct research towards specifying threshold values which would define 'Good Environmental Status' (GES) for underwater noise. Here, we chart the progress made during the first decade of Descriptor 11's implementation: 2010-2020. Several international joint monitoring programmes have been established for impulsive and continuous noise, enabling ecosystem-scale assessment for the first time. Research into the impact of noise on individual animals has grown exponentially, demonstrating a range of adverse effects at various trophic levels. However, threshold values for GES must be defined for 'populations of marine animals.' Population-level consequences of noise exposure can be modelled, but data to parameterise such models are currently unavailable for most species, suggesting that alternative approaches to defining GES thresholds will be necessary. To date, the application of measures to reduce noise levels (quieting/noise abatement) has been limited. To address this, the EU in 2021 identified an explicit need to reduce underwater noise pollution in its waters. Delivering on this ambition will require further research focused on the development and implementation of quieting measures.

Effect of Pile-Driving Sounds on the Survival of Larval Fish.

Concern exists about the potential effects of pile-driving sounds on fish, but evidence is limited, especially for fish larvae. A device was developed to expose larvae to accurately reproduced pile-driving sounds. Controlled exposure experiments were carried out to examine the lethal effects in common sole larvae. No significant effects were observed at zero-to-peak pressure levels up to 210 dB re 1 µPa(2) and cumulative sound exposure levels up to 206 dB re 1 µPa(2)·s, which is well above the US interim criteria for nonauditory tissue damage in fish. Experiments are presently being carried out for European sea bass and herring larvae.

The European Marine Strategy: Noise Monitoring in European Marine Waters from 2014.

The European Marine Strategy Framework Directive requires European member states to develop strategies for their marine waters leading to programs of measures that achieve or maintain good environmental status (GES) in all European seas by 2020. An essential step toward reaching GES is the establishment of monitoring programs, enabling the state of marine waters to be assessed on a regular basis. A register for impulsive noise-generating activities would enable assessment of their cumulative impacts on wide temporal and spatial scales; monitoring of ambient noise would provide essential insight into current levels and any trend in European waters.

Protection of Marine Mammals.

Within the European Defense Agency (EDA), the Protection of Marine Mammals (PoMM) project, a comprehensive common marine mammal database essential for risk mitigation tools, was established. The database, built on an extensive dataset collection with the focus on areas of operational interest for European navies, consists of annual and seasonal distribution and density maps, random and systematic sightings, an encyclopedia providing knowledge on the characteristics of 126 marine mammal species, data on marine mammal protection areas, and audio information including numerous examples of various vocalizations. Special investigations on marine mammal acoustics were carried out to improve the detection and classification capabilities.

Controlled Sonar Exposure Experiments on Cetaceans in Norwegian Waters: Overview of the 3S-Project.

In mitigating the risk of sonar operations, the behavioral response of cetaceans is one of the major knowledge gaps that needs to be addressed. The 3S-Project has conducted a number of controlled exposure experiments with a realistic sonar source in Norwegian waters from 2006 to 2013. In total, the following six target species have been studied: killer, long-finned pilot, sperm, humpback, minke, and northern bottlenose whales. A total of 38 controlled sonar exposures have been conducted on these species. Responses from controlled and repeated exposure runs have been recorded using acoustic and visual observations as well as with electronic tags on the target animal. So far, the first dose-response curves as well as an overview of the scored severity of responses have been revealed. In this paper, an overview is presented of the approach for the study, including the results so far as well as the current status of the ongoing analysis.

Common sole larvae survive high levels of pile-driving sound in controlled exposure experiments.

In view of the rapid extension of offshore wind farms, there is an urgent need to improve our knowledge on possible adverse effects of underwater sound generated by pile-driving. Mortality and injuries have been observed in fish exposed to loud impulse sounds, but knowledge on the sound levels at which (sub-)lethal effects occur is limited for juvenile and adult fish, and virtually non-existent for fish eggs and larvae. A device was developed in which fish larvae can be exposed to underwater sound. It consists of a rigid-walled cylindrical chamber driven by an electro-dynamical sound projector. Samples of up to 100 larvae can be exposed simultaneously to a homogeneously distributed sound pressure and particle velocity field. Recorded pile-driving sounds could be reproduced accurately in the frequency range between 50 and 1000 Hz, at zero to peak pressure levels up to 210 dB re 1µPa(2) (zero to peak pressures up to 32 kPa) and single pulse sound exposure levels up to 186 dB re 1µPa(2)s. The device was used to examine lethal effects of sound exposure in common sole (Solea solea) larvae. Different developmental stages were exposed to various levels and durations of pile-driving sound. The highest cumulative sound exposure level applied was 206 dB re 1µPa(2)s, which corresponds to 100 strikes at a distance of 100 m from a typical North Sea pile-driving site. The results showed no statistically significant differences in mortality between exposure and control groups at sound exposure levels which were well above the US interim criteria for non-auditory tissue damage in fish. Although our findings cannot be extrapolated to fish larvae in general, as interspecific differences in vulnerability to sound exposure may occur, they do indicate that previous assumptions and criteria may need to be revised.