Abstract
The European eel is a highly threatened species according the European Inland Fisheries Advisory Commission (EIFAC) and the Food and Agriculture Organization of the United Nations (FAO). The recruitment of this species has collapsed over the last fifty years primarily because of the destruction of free migration routes and overfishing. One of the most important factors linked to population decline is mortality during catadromous migration caused by hydroelectric facilities. The aim of the present study was to assess the mortality rate of silvers eel passing through two small hydroelectric facilities. Total mortality at the site was 5%, but it was 15% for fish passing through the two hydroelectric facilities. However, the cumulative mortality in the river basin studied, which has many hydroelectric facilities, indicated that silver eel escapement from the Słupia drainage basin was very low.