This study investigates the movement patterns, habitat use, and spatial distribution of sea trout (Salmo trutta) and Atlantic salmon (Salmo salar) within the River Erriff and Killary Harbour, addressing a critical knowledge gap in the region. Using acoustic telemetry, we are tracked individual fish to assess their behaviour, habitat utilization, and survival across freshwater and marine environments. This research will generate essential ecological data to inform evidence-based, sustainable management and conservation strategies. The outcomes will directly support the protection and long-term viability of salmonid populations in Ireland’s freshwater and coastal ecosystems.