Fig. 1

Locations of acoustic receiver stations in A the western Dutch Wadden Sea and northern Lake IJsselmeer and C the southern North Sea. Depth contours of the Wadden Sea indicate the upper limits of zones described by [7], ranging from areas exposed at low tide (salt marsh to low littoral) to deep sublittoral areas that are permanently below mean low water spring tide (MLWS) and reach maximum of ~ 40 m depth. B Notable locations referred to in the text, including three tidal basins (blue text) and one subregion (Balgzand). Acoustic receiver locations in panels A and C encompass multiple acoustic arrays: i) Wadden Sea—SWIMWAY, RBVV2, ii) North Sea—Apelafico, bpns, cpodnetwork, FISHINTEL, Haringvliet, Orstedcod, PelFish, ws1, and iii) Fresh water—Brasem IJM/MM. Only receivers with mullet detections are included in panel C. Additional detection data were obtained via the database of the European Tracking Network: https://www.lifewatch.be/etn/