Migratory salmonids as vectors of carbon, nitrogen and phosphorus between marine and freshwater environments in north-east England

This study provides estimates of fluxes between freshwater and marine environments of organic carbon (C), nitrogen (N) and phosphorus (P) transported by migrating Atlantic salmon and sea trout. Mean annual values were assessed for a group of seven rivers in north-east England over a 7-year period (1989–1995). The total annual import to the rivers via adults of both species ranged between 48.5 and 156.8 t C, 10.5–34.1 t N and 1.7–5.3 t P. Total annual export by smolts and kelts ranged between 20.3 and 71.5 t C, 4.5–15.9 t N and 0.75–2.6 t P. The net flux of each of C, N and P by these fish represented only 0.09–0.24% of the total annual river loads. The net marine import of each element represented approximately 75% of the gross adult import. Migratory fish provide the only direct source of such materials to the upper reaches of rivers.