Development of a large-scale juvenile density model to inform the assessment and management of Atlantic salmon (Salmo salar) populations in Scotland

•Fish data from 25 organisations, 179 Catchments, 1861 sites, 3848 visits, 19 years.•Landscape proxies for habitat derived from large-scale spatial datasets.•Capture probability model harmonises complex and diverse dataset.•Density model allows national scale predictions of juvenile abundance.•Benchmark developed from density model provides basis for juvenile assessment.