Piscivority by Stocked Brown Trout (Salmo trutta) and Its Impact on the Nongame Fish Community of Bottom Creek, Virginia

Abstract

The magnitude of fish consumption by brown trout (Salmo trutta) was assessed by experimentally stocking large (> 280 mm) and small (< 280 mm) brown trout in separate sections of a Virginia stream. Large brown trout ate five species of fish consistently during the May–November, 1979, experimental period; by November, every trout stomach examined contained fish remains. Small trout rarely ate fish. Effects of fish consumption were apparent in trout growth and in abundance of prey species. Large trout grew 9.4% in length and 21.3% in weight, whereas small trout grew 4.5% in length and 4.7% in weight. Abundance of the major prey species, torrent sucker (Moxostoma rhothoecum), decreased between April and October in the stream section containing large trout, but remained constant in a comparable reference section; estimates of total consumption of torrent suckers by brown trout accounted for a large portion of the decrease in abundance. Predation on torrent suckers was selective for smaller individuals. The field experiment indicates that stocking large-sized brown trout may enhance growth and survival of brown trout, but that standing crops of nongame species are likely to decline.Key words: brown trout, nongame fishes, predation, stocking strategy, stream ecology