Translocation and introduction of non-indigenous species might be considered as one of the least reversible human induced changes in nature. The background factors of a successful biological invasion are diverse; and the complete eradication of established invasive species seems practically impossible. The aim of our presentation is to (1) revise the trends and spreading mechanisms of non-indigenous species; (2) assess the potential ecological risk of new species in the catchment basin of a shallow lake (Lake Balaton, Hungary) and (3) to analyze the local and regional factors affecting the distribution patterns of gibel carp (Carassius gibelio), an effective invasive species of the region, based on recent case studies.
Hungary have central position in the Danube water system and have considerable fishery sector, therefore plays a crucial role in the spreading of non-native fish species. According to our literature review, the number of already identified non-indigenous species is more than 60, which is higher than the number of natives. The trends of new introductions seem to increased recently, due to the uncontrolled aquarium fish releases. Recent (between 2011 and 2015) standardized countrywide surveys indicated that non-indigenous species occurred in 78.7% of 767 study sites. The most abundant species were gibel carp (Carassius gibelio) and topmouth gudgeon (Pseudorasbora parva). Their occurrence is strongly related to presence of aquaculture facilities.
The ecological risk assessment of Balaton-catchment was carried out by using the Fish Invasiveness Screening Kit (FISK), which proved that gibel carp and Ponto-Caspian Gobiidae posing the greatest threat.
Since gibel carp seems to be the most important invasive species, the relationship between abundance patterns, environmental conditions, management practices (within 11 lentic habitats), and also in long-term abundance changes (datasets from standard localities of Kis-Balaton Waterprotection System between 1986 and 2011) were analyzed. High abundances of gibel carp strongly associated with habitat desiccation and also long-term analyses indicated that after a 'boom-bust' period, the abundance of the species might stabilized in a less disturbed system.
These results highlight the necessity of management interventions in invaded habitats as well as the development in a more effective national level (regional scale) controlling system. These may reduce the possibility of unintentional non-indigenous fish translocations between catchments.
This project was supported by the "GINOP 2.3.2 -15-2016-00004: Establishing the sustainable angling-aimed management of Lake Balaton."; the HORIZON2020 678396 TAPAS project and the "EFOP-3.6.3-VEKOP-16-2017-00008" projects. Árpád Ferincz and Ádám Staszny was supported by the Bolyai János Postdoctoral Fellowship of the Hungarian Academy of Sciences.