Top down effects of stocked fish in Alpine lakes
Robert Schabetsberger, University of Salzburg (AT)
Stocking fishless alpine lakes dates back to medieval times, but with the use of helicopters stocking activities have increased in the past decades. We present several cases of subalpine and alpine lakes in the Austrian Alps where introduced fish eradicated natural plankton and amphibian communities. Once the stocked fish started to reproduce, the metazoan plankton communities changed from large, pigmented crustacean species to a dominance of rotifers. Fish preyed heavily on eggs and larvae of natural amphibian species. Lake Sulzkarsee in the National Park Gesäuse has been stocked with minnows (Phoxinus phoxinus) in the 1970s. Two limnological studies have been conducted in the past decade and show strong top-down effects of introduced minnows. In an ongoing project we are trying to eliminate introduced fish from the lake.