The movement of hatchery-reared rainbow and brown trout in a polluted river in the South Wales coalfield

Hatchery reared rainbow and brown trout (length 20 cm) were released in March 1974 and April 1975 respectively into the Taff Bargoed, a small river in South Wales, polluted by coal wastes and containing a low resident population of brown trout. From subsequent electro-fishing surveys and catch returns from anglers, extensive downstream movements occurred in both species. About 50% had either been caught or had moved out of the river, a distance of about 5 km, after two weeks and after two months only some 10 % remained. Within the fishing season it was estimated that 3 and 22% of brown and rainbow trout respectively were caught.