Abstract
A total of 56 salmon was tagged in the Usk estuary using combined acoustic and radio tags. Those fish migrating within the estuary oscillated with the tide over c . 10 km, being towards the seaward end at low water and moving upstream on the flood tide. Fish migrating through the estuary moved upstream on the flood tide and stemmed displacement downstream during the ebb. These findings, together with information on the hydrodynamics of the estuary, indicate that the fish utilize tidal currents to migrate passively in their preferred direction.