The migratory behaviour of juvenile and adult salmonids in relation to an estuarine barrage

There is wide concern regarding the effects that estuarine barrages may have on estuarine environments and the species which utilise them. Of particular concern are the possible effects on diadromous fish which move between fresh and salt water. This paper presents results from a 3 year investigation (1993–95) of the migratory behaviour of both juvenile and adult salmonids undertaken in the vicinity of a barrage on the River Tawe in South Wales, which was completed in 1992. The localised upstream movements of acoustically tagged returning adult salmonids (n = 28) were investigated in the immediate vicinity of the barrage and associated fish pass using a High Resolution (HiRes) tracking system. The behaviour of salmonid smolts (n = 52), tagged with miniature acoustic transmitters, were also monitored during their spring seaward emigration within the impounded estuary.