The effect of brown trout (Salmo Trutta L.) on stream invertebrate drift, with special reference to Gammarus pulex L

The effect of brown trout (Salmo trutta L.) on invertebrate drift density was examined in three previously fish-free springbrooks. Drift density was studied during the day following the sequential introduction of: 1) empty cages, 2) cages containing trout, and 3) empty cages. Each period lasted three whole days, and drift density was measured at daytime and night-time every day. Control drift density was determined using empty cages in two similar springbrooks. Night-time drift density of large Gammarus pulex L. (>3.9 mg DW/ind) decreased compared to that of smaller size-groups following trout introduction, and was significantly lower (p