Odontocete Occurrence in Highly Trafficked European Straits: Insights from Static Acoustic Monitoring

Static Acoustic Monitoring (SAM) using C-PODs, deep C-PODs, and F-PODs was conducted as part of the STRAITS project (Strategic Infrastructure for improved animal Tracking in European Seas), funded under the EU’s Horizon research and innovation programme, to investigate odontocete acoustic occurrence across four European straits: the North Channel, the Sound, the Strait of Gibraltar, and the Dardanelles Strait. The acoustic presence of dolphin species and harbour porpoises was modelled in relation to tidal cycle, moon phase, sea surface temperature (SST), diel period, season, and Sound Pressure Levels (SPLs), representing ambient underwater sound using a Generalised Additive Modelling (GAM) approach. Harbour porpoises were primarily detected in the Sound and the North Channel, while dolphin detections were higher in the Strait of Gibraltar and the Dardanelles Strait. There was a significant association with SPLs on both species across all locations where it was assessed. There was a significant effect of tidal cycle and SST on both species across all locations except the Dardanelles Strait. Temporal patterns were significant across species and study sites. This study presents the first multi-strait assessment of odontocete occurrence in key marine corridors, highlighting the relationship of environmental and temporal drivers, underwater noise, and odontocete occurrence, and providing insights for marine spatial planning and conservation management in highly trafficked regions.