A two-year radio-tracking study of Atlantic salmon was conducted on the Aulne, a small French coastal river. The objective was to investigate patterns of upstream migration of salmon, in particular through the lower 70 kilometres of the river which is canalised. This enabled us to compare the passability of weirs and how this varied according to the type of fish-pass facility. The study also enabled both an estimation of the impact of fishing activities and a comparison of the upstream migration capacities of wild and reared salmon.