Data collection:
Between April 2021 and July 2022 click detectors were deployed off Sherkin Island in Roaringwater Bay (51°27’40.7”N, 9°26’24.7”W), a Special Area of Conservation (SAC) for harbour porpoise. Porpoise occur in the bay throughout the year, peaking in autumn months, with an estimated population (in 2008) of 117-201 individuals (NPWS, 2014), although density estimates have reportedly declined in recent years with the 2020 estimate of 0.61 individuals per km2 (O’Brien & Berrow, 2020). The deployment site is a relatively sheltered site on the southwest coast of Sherkin Island, approximately 18m water depth, with a predominantly sandy seafloor. A C-POD and F-POD were co-deployed on a mooring line anchored to the seabed, positioned 5m above the seabed, side by side in a custom-built acetal plastic frame to optimise simultaneous detections on both devices (Appendix, Figure S1). The devices were retrieved and redeployed every 3-4 months to ensure continuity of acoustic recordings.