Movements of Atlantic salmon, Salmo salar L., in an estuary in south‐west England

Abstract

In the years 1985–1987, salmon were tracked in the estuary of the River Fowey, Cornwall using the ‘sonar buoy’ system developed at the M.A.F.F. Fisheries laboratory and described by Solomon & Potter (1988). Sixty‐one salmon were caught and tagged in the estuary, 25 with radio and 36 with combined radio and acoustic transmitters. About half these fish were not recorded entering the freshwater reaches of the R. Fowey, and from tag recoveries it seems likely that about 27% were returning to other rivers. For fish returning to the R. Fowey the time between tagging and entry into fresh water varied between 9 h and 130 days. In the estuary the fish largely moved in the same direction as the tidal currents, although movements over the ground against the current were more common in the bottom 2 km and the top 2 km. During periods of low river‐flow in summer all salmon tracked in the estuary dropped back out to sea where they stayed for varying periods: some of these made several sorties past the estuary mouth and on occasions well up the estuary before finally entering fresh water. During periods of higher river discharge, in both the summer and the autumn, some fish remained in the estuary for longer periods, sometimes holding position in deep, sheltered water. Most fish entered fresh water at night during periods of increased freshwater discharge, although at very high flows fish also entered in daylight.