Movement of adult Atlantic salmon in the Usk estuary, Wales

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.     

The seaward movement of Atlantic salmon smolts in the Usk estuary, Wales, as inferred from power station catches

The greatest numbers of Atlantic salmon smolts were caught at Uskmouth power station during the day on the flood tide and the least on an ebbing night tide. Catch rates during the day on an ebb tide and at night on a flood tide represented an intermediate state. The results, together with tracking data, suggest that salmon smolts prefer to migrate seaward through the lower Usk estuary during the night Oncc an ebbing tide.     

The benthic ecology of river estuaries entering the Severn Estuary

The fauna of the Rivers Avon, Usk and Wye was similar to that for soft sediment in the Severn Estuary. It was dominated by Nereis diversicolor, Corophium volutator, Aiacoma balthica and oligochaetes. Maximum densities of Corophium and Macoma were higher than in the main estuary, while that of Nereis was similar. Distributions of dominant species showed gradients along river length and across river profile. These are discussed.