L. Forró szerk.: Miscellanea Zoologica Hungarica 8. 1993 (Budapest, 1993)

Vida, A.: Threatened fishes of the Szigetköz

MISCELLANEA ZOOLOGICA HUNGARICA Tomus 8. 1993 p. 25-34 Threatened fishes of the Szigetköz by A. Vida (Received June 17, 1993) Abstract: Szigetköz, a section of the Danube river system, represents many water types found in Hungary. 65 of the 80 fish species native to Hungary have been reported from this territory, being thus the richest region considering species number. Key words: river ecological indicators, fish fauna, changing environment, river regulation, hydropower dams, threatened species, Szigetköz Introduction The section of the Danube river system called "Szigetköz" (Fig. 1), which was originally a side arm system, represents many water-types found in Hungary. Out of the 80 native fish species of Hungary 65 have been recorded in this territory (Vida 1990a, 1990b). There is no other region of the country with comparable species-richness. 30 percent of the fish species is considered as stenoecious, in other words they are restricted to certain specific aquatic habitat types. The water bodies of the Szigetköz can be classified into six main hydrogeographical categories, as follows (Vida 1990a, 1990b): - main channel; - connected backwaters (side river-branch system of the flood plain); - irrigation channels outside the flood plain; - backwaters of the flood free area; - ponds of gravel-pits; - Mosoni-Duna, which is a side arm of the main channel. Methods and material The selection of the fish sampling sites was based on the following aspects: - sampling of the whole geographic area should be done; - including all the water types; - inclusion of sites with special circumstances; sites of our former collections; - partial overlapping with previous sampling sites of other hydrobiological studies. The applied fishing methods were as follows: - electric research fishing-machine; - framed fry-catcher; - seines, with different mesh-size; - drift-nets, with different mesh-size; - lift-nets. These combined methods provided an effective sampling. Our results therefore differ considerably from the capture data of the local fishermen of the different age groups of fishes throughout the whole study area.