engleski

Change of native fish community after closure of the water reservoir on river Butoniga (Istria, Croatia)

The water reservoir Butoniga (210 ha) on river Butoniga was established in 1989. During the investigation period of 1989, 1990, 1991 three incoming streams and a new reservoir was populated with Leuciscus cephalus albus, Gobio gobio, Alburnus albidus, Tinca tinca, Barbus plebejus, Phoxinus phoxinus, Padogobius martensi and Anguilla anguilla. The reservoir was of the cyprinid type with dominant populations of Leuciscus cephalus albus and Barbus plebejus. The primary structure of the fish community is described. 'The new environment developed by water reservoir as well as the suggestion by fisheries biologists to introduce grass and the silver carp to reduce enormous algal and herbaceous material in a lake drastically changed the fish community. In the year 2000 a new ichthyological investigation was carried out and the structure of the fish community reexamined. Now, 10 years since the first use of the reservoir, the dominant species are Cyprinus carpio and Esox lucius that were illegally introduced by sports fishermen. All the autochthonous species decreased with extreme apparent diminution of the endemic Adriatic species Padogobius martensi (Gunther, 1861) present only in two Croatian rivers, Zrmanja and Mirna. This species also occurs in Slovenia and Italy. Within the lake Barbus plebejus disappeared. The frequent creation of water reservoirs on karstic rivers will cause the disappearance of endemic native ichthyofauna, especially species that have a high biodiversity value. For example, compared to the Italian population in the western Adriatic watershed, populations of Padogobius martensi show morphological and probably other differences. These fish are not included in fish stocking; therefore, they have a high value in determining the natural boundaries of some river water systems. As small predators in the freshwater system of the Adriatic rivers, these fish are an important link in the trophic chain.

fish community; endemic native ichthyofauna; Adriatic river system

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