Abstract
The predation impact of recently stocked triploid brown trout, S almo trutta L., on migrating wild A tlantic salmon, S almo salar L., smolts was investigated in two field‐based experiments. The first experiment employed a unique experimental facility to monitor 57 wild S . salar smolts through an enclosure containing a known density of stocked S . trutta to determine a predation rate. None of these smolts were preyed upon by the stocked S . trutta . The second experiment investigated the diet of free‐ranging stocked triploid S . trutta in a chalk stream during the spring. Although at least 6% of the free‐ranging stocked triploid S . trutta became piscivorous on P hoxinus phoxinus (L.), the results suggest that large, recently stocked, triploid S . trutta with a high condition factor do not represent a predation threat to wild S . salar smolts. However, it is recommended that a precautionary approach is maintained and the findings are not generalised until further investigation permits explicit management advice to be developed, and that the stocking of large triploid S . trutta is avoided before May/ June (regional variations to apply) each calendar year, where this can reasonably be achieved.