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Action C5 - Control and eradication of the Silurus glani
The fresh water ecosystems risk to be invaded by the allochthonous species, more than other ecosystems, since it is easier for such species to scatter along the superficial hydrographic network. In Italy there are 48 autochthonous fresh-water species, 38 are allochthonous, 13 out of which are now naturalized. One of the emblematic cases of invasive species is that of the welsh catfish Silurus glanis
(Linnaeus, 1758), whose predatory impacts on the autochthonous species of northern Italy led to a significant reduction in the number of many species. The welsh catfish is a big-sized fish, the adults can reach a total length of 2.5 meters and a weight of 200 Kg. It is characterized by a long and laterally pressed body with a large head equipped with a very large mouth surrounded by barbels. It has very small eyes and a very developed sensorial apparatus as regards its chemo-receptive and electro-receptive element, which proves the habits of this species usually living in slowly flowing rivers with muddy water, being active mainly at night. The range of distribution of this species extends from Germany to southern Sweden, including the whole Balkan region up to Turkey, northern Iran and Aral Sea. Starting from its original range, the welsh catfish has been introduced in many other European countries since the 20th century, mainly for the purposes of aquaculture and recreational fishing. In Italy the species has been present since 1930, with the first naturalized populations registered since the 1970s in the Po river (COPP et al., 2009). As regards the presence and distribution of the species in the Sile river, the available information report that its presence has been registered only in the part of the river situated south of Treviso. The results of the previous surveys include data gathered from the three Provincial Fishing Maps, from the Sile Park's Fishing Map and from specific studies dedicated to the knowledge of the presence and distribution of allochthonous species. At present there are no available data regarding the exact density and biomass of the welsh catfish in the Sile river since no scientific studies about it have been carried out so far.
Nevertheless, the species has been clearly observed by fishermen and registered through monitoring activities carried out through the technique of the visual census.
The proposed action aims to find and normalize the most suitable practices to combat, limit and possibly eradicate the welsh catfish, guaranteeing the conservation of the autochthonous fish populations of the Sile river, as well as the restoration of the ecological balance of the whole ecosystem.
The interventions for the control and eradication of the welsh catfish will be carried out mainly in those stretches of the river where the action A3 will register the most numerous and better structured populations. The preliminary action will be also used as an initial check of the distribution of the allochthonous species along the whole course of the Sile river and by the confluence of the different tributaries.