Pile driving is one of the most intense anthropogenic noise sources in the marine environment. Each foundation pile may require up to a several thousand strokes of high hammer energy to be driven to the embedded depth. Scientific evidence shows that effects on the marine environment have to be anticipated if mitigation measures are not applied. Effective mitigation measures to prevent and reduce the impact of pile driving noise should therefore be part of regulation. The role of regulators is to demonstrate and assess the applicability, efficiency and effectiveness of noise mitigation measures. This requires both, scientific knowledge on noise impacts and the consideration of normative aspects of noise mitigation. The establishment of mitigation procedures in plans and approvals granted by regulatory agencies includes several stages. Here, we outline a step-wise approach in which most of the actions described may be performed simultaneously. Potential measures include the appropriate maritime spatial planning to avoid conflicts with nature conservation, site development for offshore wind farms to avoid undesirable activities in time and space, coordination of activities to avoid cumulative effects, and the application of technical noise abatement systems to reduce noise at the source. To increase the acceptance of noise mitigation applications, technical measures should fulfil a number of requirements: (a) they are applicable and affordable, (b) they are state-of-the-art or at least advanced in development, (c) their efficiency can be assessed with standardised procedures. In this study, the efficiency of noise mitigation applied recently in offshore wind farm construction projects in the German North Sea is explained and discussed with regard to the regulation framework, including the technical abatement of impulsive pile driving noise.

In previous studies, the contribution of Love waves to the primary micoseismic noise field was found to be comparable to those of Rayleigh waves. However, so far only few studies analyzed both wave types present in this microseismic noise band, which is known to be generated in shallow water and the theoretical understanding has mainly evolved for Rayleigh waves only. Here, we study the relevance of different source region parameters on the observed primary microseismic noise levels of Love and Rayleigh waves simultaneously. By means of beamforming and correlation of seismic noise amplitudes with ocean wave heights in the period band between 12 and 15 s, we analyzed how source areas of both wave types compare with each other around Europe. The generation effectivity in different source regions was compared to ocean wave heights, peak ocean gravity wave propagation direction and bathymetry. Observed Love wave noise amplitudes correlate comparably well with near coastal ocean wave parameters as Rayleigh waves. Some coastal regions serve as especially effective sources for one or the other wave type. These coincide not only with locations of high wave heights but also with complex bathymetry. Further, Rayleigh and Love wave noise amplitudes seem to depend equally on the local ocean wave heights, which is an indication for a coupled variation with swell height during the generation of both wave types. However, the wave-type ratio varies directionally. This observations likely hints towards a spatially varying importance of different source mechanisms or structural influences. Further, the wave-type ratio is modulated depending on peak ocean wave propagation directions which could indicate a variation of different source mechanism strengths but also hint towards an imprint of an effective source radiation pattern. This emphasizes that the inclusion of both wave types may provide more constraints for the understanding of acting generation mechanisms.

The Marine Strategy Framework Directive (MSFD) has been an important driver for progress in monitoring and assessment of impulsive underwater noise in the marine environment of the European Union. An important achievement of the MSFD implementation was the development of regional noise registries, providing the data basis for assessments. Recently, the EU has made tremendous efforts to propose harmonized assessment approaches and first-of-their-kind regional quantitative thresholds for impulsive underwater noise. In light of these newly developed thresholds values, we analyze the suitability of the available data in the noise registries for assessment purposes under the MSFD and review sources of uncertainties regarding quantitative results. We present three regional case studies located in the North Sea, the Baltic Sea and the Mediterranean Sea. For each of these regions, a sound-intensive activity was selected that aligned with a realistic impulsive noise event reported for the region. We made use of available data in the noise registries and applied the EU Guidance recommended for the description of impulsive noise sources, but also used alternative approaches and observations as comparison. The case study analysis includes the evaluation of data availability, data quality and data accuracy in the noise registries, and identifies corresponding consequences of the data for the uncertainty and interpretability of assessment results, especially for the quantitative evaluation of habitat areas impacted by noise. Finally, we make suggestions for the improvement of the data basis in the noise registries and the optimization of the assessment accuracy.

Anthropogenic noise in most parts of the Earth’s oceans is increasing. If not managed appropriately, it has the potential to significantly impact marine mammals and their ability to interact with their environment. Marine mammals rely heavily on sound for critical life functions, and anthropogenic noise can interfere with sound sensing and usage, through masking, behavioral disturbance, stress, noise-induced temporary hearing loss, and, in extreme cases, injury to tissues and organs. Depending on the severity and context of a noise exposure, noise-induced impacts to individual animals could translate to population-level impacts. This chapter highlights the importance of managing anthropogenic noise, identifying limitations in existing management approaches, and briefly covering management approaches from different jurisdictions. Significant gaps in our understanding of species responsiveness to anthropogenic noise, the status of existing marine mammal populations, and characterization of underwater noise sources present challenges for the robust prediction and management of underwater noise. Based on current knowledge, a best-practice approach to the management of anthropogenic noise is presented whereby management might best achieve desired environmental outcomes. A focus on desired environmental outcomes provides a framework for robust, adaptable, and context-dependent management of underwater noise that more effectively supports species conservation.

The effect of potential mitigation measures under discussion in the context of managing underwater radiated noise from ships is analyzed by means of a parametric study. These measures include slow steaming, route optimization (in terms of energy efficiency, weather conditions, or avoidance of sensitive areas), and source mitigation, characterized by intrinsic reduction in source level and aimed at achieving compliance with class notations (underwater radiated noise limits). The study focuses on specific scenarios such as the port-to-port routing of commercial ships in the North Sea and offshore service traffic related to maintenance and operation of offshore wind farms. The underwater radiated noise is computed via a parametric approach (linear model) based on input parameters over time, e.g., ship source level (among others as a function of ship type, length, speed, etc.), speed, position, etc. The exposure of marine mammals and the affected area are derived using frequency-weighted noise criteria (e.g., LF, HF hearing groups). Different acoustic evaluation metrics and approaches are analyzed and compared. On the one hand, the study shall outline promising parameters to adjust to efficiently minimize underwater noise; on the other hand, it aims to derive evaluation approaches to assess the effect of potential future regulations on underwater noise. The work we present is the outcome of ongoing research and development projects such as the Interreg project DEMASK in which the effect of potential developments and mitigation measures on underwater radiated noise within the North Sea is assessed.