A fish selective obstacle to prevent dispersion of an unwanted fish species, based on leaping capabilities

The European minnow, Phoxinus phoxinus (L.), constitutes a serious threat to natural brown trout, Salmo trutta L., stocks in Norway following its introduction and translocation. In the present study, the leaping capabilities of the European minnow (50-110 mm total length) and brown trout (64-255 mm total length) were investigated with the aim of constructing suitable waterfall barriers to prevent further unwanted dispersal of the minnow, but still allow passage of larger brown trout. No successful leap of minnows was recorded at 4.9-6.5 degreesC, even at height intervals as low as 3 cm. At 14.0-16.5 degreesC, minnows were able to force waterfall barriers up to 27 cm high. At 4.9-6.5 degreesC brown trout forced waterfall barriers up to 40 cm. Thus, building of such barriers in brooks and rivers can help prevent the dispersal of minnows, and still allow larger brown trout to pass during feeding and spawning migrations.