Long-term changes in fish populations of acid streams and lochs in galloway South West Scotland

Abstract

During 1978–79, and again in 1984, fish populations were surveyed in 22 lochs and 27 streams in Galloway, southwest Scotland. Chemical analyses of these waters and of bulk precipitation were made over the same period. The study area includes moorland catchments and catchments with young or semi-mature coniferous forest. Trout were not caught in nets set in 5 lochs which were known to contain fish in the past. Angling records also indicated a decline in catches and increased average weight of trout in two other lochs. Evidence for the decline in fish populations suggests that this process has occurred over a period of at least 50 yr. In fishless lochs and streams the levels of acidity and Al were in the range known to be toxic to fish. Stream acidity and sulphate concentrations were significantly higher in catchments with semi-mature coniferous forests. The available evidence for long-term acidification of Galloway lochs and streams is discussed and it is concluded that acid depositions are likely to be the major cause of changes in the status of fisheries in this region.