Résumé
In France, the increasing demand for decarbonized energy production has led to a rapid expansion ofoffshore wind farm (OWF) deployment, with over 15 projects currently in progress. The introduction of these anthropogenic structures in the marine environment is likely to influence space use and habitat connectivity of fish. OWFs can act as artificial reefs for certain fish communities with species exhibiting high residency and/or site fidelity patterns for these new habitats. On the other hand, pressures generated by OWF, such as noise emissions, may repel certain species and modify movement and migration behaviour. Considering the ecological functions and socio-economic importance of fish communities, these effects need to be assessed through comprehensive and long-termmonitoring. The collaborative FISHOWF project (2021-2024) used acoustic telemetry to identify how mobile fish species use and connect different habitats across OWF development areas in the Channel, Atlantic and mediterranean Sea. This monitoring method involves using sound-emitting tags and underwater receivers to track fish movements. This project relied on dedicated receiver arrays deployed within 4 OWF, combined with the region-wide acoustic telemetry networks FISHINTEL (Channel), CONNECT-MED & RESMED (Mediterranean) to monitor over 400 fish/crustaceans (including sea bass, pollack, lobster, sharks and rays). Protocols using acoustic telemetry at different spatial scales were tested, including a fine-scale positioning approach to track movement behaviour near anOWF structure. Key results include the identification of important existing habitats for several species in OWF underconstruction, temporary residency and site fidelity of two elasmobranch species within an operational OWF, anddetections within OWF areas of several migratory species travelling across the Channel.FISHOWF demonstrated the relevance of using acoustic telemetry at multiple spatial scales to identify and evaluatespecific effects of OWF and their grid connection on fish. Results contribute to improving ecological knowledge on monitored species, to better assess habitat modifications induced by OWF from the seafloor to the surface, and to better understand the ecological role of these artificial structures (e.g. refuge, essential habitat, ecological traps).The follow-up project FISHOWF+ (2024-2027) will maintain and expand this acoustic telemetry monitoring to up to6 OWF (fixed-bottom and floating OWF) and aims to: • optimize the acoustic telemetry network within the OWF& development zones to characterise fish aggregation and reef effect at different spatial scales (e.g. Substation vsOWF scale) • assess in situ behaviour of electrosensitive species near a substation & dynamic cable of a floating turbine and provide insights into potential electromagnetic field effects • examine how OWF construction activities impact fish habitat use• address knowledge gaps on regional connectivity at EUscale and the ecological role of OWFThe ongoing and future efforts of the FISHOWF and FISHOWF+ projects underscore the importance of comprehensive monitoring and research to understand the ecological impacts of offshore wind farms. By leveragingadvanced technologies like acoustic telemetry, these projects aim to provide valuable insights into the interactions between marine life and OWFs, ultimately guiding sustainable development and management practices that balance energy production with marine conservation. Findings will not only enhance scientific understanding but also inform policy decisions, ensuring that the expansion of renewable energy infrastructure integrates and promotes marine ecosystem health.