Threshold-Based Assessment of Underwater Noise Pollution in French Marine Waters

Since underwater noise has been recognized as a source of pollution, affecting all compartments of underwater ecosystems, efforts have been made to reduce its effects and design management tools to assess and regulate it. Consequently, over the last decades, governance regulations have been implemented internationally, and converging risk assessment methodologies emerged to define threshold values. However, including the complexity of impacts on species and marine habitats at the heart of the process is an ambitious challenge. Given the sparseness of the knowledge, it is difficult to define and set threshold values for common regulation and management. The aim of this chapter is to investigate risk assessment conditions in regard to threshold value setting. The assessment framework relies on the definition of a sound pressure-level threshold, related to biological impacts, and temporal and spatial thresholds, related to habitat degradation. As the choice of thresholds still needs to be researched, several ranges of values for each threshold are investigated to estimate their relationships in the decision-making process. This chapter focuses on a practical implementation of a threshold-based assessment over the French coasts. It demonstrates how noise mapping can effectively support regulators to identify and prioritize impacted areas depending on availability of scientific knowledge.