Long-term changes in the fish community of Neusiedler See (Burgenland, Austria)

Summary

In the course of establishing the National Park Neusiedler See-Seewinkel, an investigation of the fish community of Neusiedler See on the Austrian/Hungarian border was carried out between 1990 and 1992.

According to the literature, 19 indigenous fish species occur in the lake. In addition another ten species have occasionally been found in the lake but they are usually confined to the small tributaries of the catchment area. Seven alien species were introduced by stocking to enhance the professional fisheries (e.g., Anguilla anguilla, Ctenopharyngodon idella) or by aquarists (e.g., Lepomis gihhosus). Comparing the results of the present study with those of investigations before 1960, marked changes in species composition and abundance can be observed: four indigenous species have disappeared completely (Umbra krameri, Leucaspius delineatus, Misgurnus fossilis, Proterorhinus marmoratus) and the abundance of several species has declined considerably (e.g., Tinca tinca) while others, especially planktivorous species (e.g., Pelecus cultratus, Alburnus alburnus), show a pronounced increase in population density.

The possible reasons for these changes are:

• 1. Human impact on the hydrology of the lake, especially water level regulations, has led to a loss of habitats within the reed belt due to drying out.

• 2. The eutrophication during the 1970s is probably responsible for the tremendous increase in abundance of the cyprinid populations, especially of the planktivorous species.

• 3. The introduction of alien species is the most direct way of disturbing the indigenous fauna. Stocking with Ctenopharyngodon idella led to the almost complete disappearance of the submerged macrophytes, resulting in the loss of an important spawning habitat for many species. Also since 1975 about 4000000 glass eels have been introduced annually. Competition and predation byAnguilla anguilla are most probably key factors in the disappearance of small species.