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

Vida, A.: Expected effects of the Gabčikovo river barrage system on the ichthyofauna of the Szigetköz and its values

Fig. 5. Qualification of the Mosoni-Duna and the expected effects according to the number of valuable fish species. Conclusions 1. Most of the fish disappeared from the Szigetköz, the most sensitive being the rare (valuable) species. 2. 38 percent of the fish species found in the Szigetköz (n=65) is falling under any of the four threatened categories of Lelek (1987), while species endemic to East Europe (e.g. Umbra krameri) are left beyond consideration. On the national level, 25 percent of the species (n=16) is protected (MN Elnöki Tanács 1982,1988). 3. On the European level (Lelek 1987) the number of endangered species is 14 (22%), number of rare species is 14 (22%) and number of vulnerable ones is 22 (43%). 4. Amount of fish disappeared or perished according to the annual fishing statistics (the annual fish catch multiplied by 3 to 5) 150-450.000 kg, accounting for several millions of individuals. Due to the divertion, the populations of 91 percent (n=59) of fish species in the Szigetköz has reached a critically low level. From these, 45 percent (n=29) is expected to disappear within a few years, while 9 percent (n=5) has probably already disappeared. 5. The ratio of area of the main channel and flood plain to number of fish species in the Szigetköz, as compared to other fish assemblages in Europe, is prominent: 6000 ha/65 species, being probably one of the highest among comparable sub-montane zones. 6. The processes that started are irreversible from the fish biological point of view. The original assemblage can never evolve in a similar way again. When one intends to conserve the valuable species in this area, constant interactions and control are needed. These species can, however, usually not be bred in captivity, and specimens originating elsewhere do not guarantee for the genetic values of the populations in the Szigetköz. 7. The population decrease will cause a decrease also in genetic resources of less affected areas and species. 8. The species disappeared or perished can usually not be bred under artificial circumstances. The species important from the economical point of view can be reproduced in captivity, but these are not those that disappear. Our knowledge