Abstract
The European Marine Strategy Framework Directive (MSFD, 2008/56/CE) aims to achieve and maintain the 'good environmental status' (GES) of marine ecosystems, including the assessment of marine mammal populations. However, assessing their abundance and distribution is challenging due to their mobility, elusiveness, and difficult data acquisition. This article highlights the role of passive acoustic monitoring as a complementary approach to traditional methods (mainly plane and boat surveys). It also presents the conclusions and perspectives of a workshop organized at the 34th conference of the European Cetacean Society in O'Grove, Spain (18th to 20th April 2023). Building on the rich foundation established by the European Cetacean Society (ECS) in 1987, this society plays a pivotal role in advancing marine mammal research and conservation efforts across European waters. The workshop emphasized the need for harmonization of protocols, indicators, and guidelines to ensure comparability of results. The establishment of a dedicated European working group was proposed to coordinate passive acoustic monitoring efforts, foster collaboration, and share best practices. The workshop concluded that the consolidation of scientific knowledge, the development of common guidelines, and the establishment of a transnational working group would improve the understanding and conservation of these vulnerable species and their habitats.