Deterioration of the fish-species assemblage due to human impact and the pike introduction as a measure for restoration of the Lake Vlasina reservoir (Serbia, Yugoslavia).

Abstract

Since formation of the Lake Vlasina reservoir (1949-1953), its faunistic composition has changed a great deal. A pronounced human impact on it was realized through the accidental introduction of non-indigenous fish species, rather than through alteration of the native peat bog habitat by building of the reservoir. One of the autochthonous species, the minnow (Phoxinus phoxinus L., 1758) is (for all practical purposes) now extinct from the reservoir, whereas the status of two other native species, the brown trout (Salmo trutta fario L., 1758) and the brook barbel (Barbus peloponnesius Valenciennes, 1884) is very poor, as indicated by their proportion in the sample. Domination of introduced (1968-1971) Eurasian perch (Perca fluviatilis L., 1758) and the common wild goldfish (Carassius auratus gibelio Bloch, 1783) and the presence of 12 other introduced fish species from the Danubian, Aegean and Adriatic watersheds characterize this water as ruined. However, characteristics of the Lake Vlasina reservoir permit the active implementation of biological measures in restoration of this heavily degraded ecosystem. The most radical one consists of introduction of the northern pike (Esox lucius L., 1758) as a new (and for the Lake Vlasina reservoir) the most appropriate top-predator species, which should reduce the number of all other species (except salmonids). The final aim is to make productive hitherto futile efforts of salmonid fish-stocking in order to restore the salmonid status of the Lake Vlasina reservoir.