Biodiversity Status of and Threats to Freshwater Fish of Croatia and Eastern Adriatic Countries

Eastern Adriatic countries (ecoregion Dalmatia 419) have a unique array of endemic freshwater fishes. Our knowledge about the diversity of its freshwater fishes is still incomplete, many new species having been described only in recent years. It is widely held that fish biodiversity constitutes a natural resource that is valuable not only economically, but also in terms of culture and aesthetics, science and education. We have reviewed the characteristics of fish biodiversity in the eastern Adriatic countries (Slovenia, Croatia, Bosnia and Herzegovina as well as Montenegro), with a special emphasis on Croatia. Endemic species are found in the river Soča, Istria Mirna River, the region of Lika and in the Krka, Cetina, and Neretva River basins, in the Moraca and Skadar Lake. Usually, a single catchment supports between 6 and 10 species. Out of the 52 European threatened freshwater species, 28% occur in the eastern Adriatic, making this area a hotspot for threatened freshwater fish. Conservation management of these resources should be considered critical by all the governments involved. The area of occupancy of endangered freshwater fish is declining and if this does not change and if the loss of species continues at the current rate, the opportunity to conserve many of the remaining species will vanish. The speciation processes of endemic species started here about 5 million years ago, but the present-day distribution patterns essentially started to be established in the Pleistocene. A special mechanism for surviving drought has evolved in these populations and in general fish in the karstic area have become very hardy; however, negative anthropogenic effects have changed much of this evolution. An overview of endemic behaviour and some examples of patterns that undermine normal existing mitigation measures are provided. Human threats to global freshwater fish biodiversity fall into five categories: over-exploitation; water pollution; flow modification; destruction or degradation of habitat; and invasion by exotic species. Combined and interacting influences on fish biodiversity are now generally well known and have been exacerbated by climate change. We believe that knowledge of these threats is insufficiently incorporated into the development of water resources development and requires wider dissemination.

Keywords: Eastern adriatic coast, Ecoregions, Endemic, Freshwater fishes.