Fish passage assessment at the most downstream barrier of the Ebro River (NE Iberian Peninsula)

Abstract

Fish passage assessment at the most downstream barrier of the Ebro River (NE Iberian Peninsula) Fish passage at artificial barriers is necessary for the conservation of healthy fish stocks. The first barrier that migratory fish encounter when ascending the Ebro River is the Xerta Weir, where a pool-type fishway was constructed in 2008. From 2007 to 2010, boat electrofishing surveys were conducted in the Ebro River downstream of the Xerta Weir to assess the potential pool of species that could use the fishway. Nine native and 12 exotic species were captured, the latter comprising 62 % of the relative abundance and 70 % of the biomass. A combination of video recording, electrofishing and trapping was used to assess the effectiveness of the fishway in facilitating the passage of fish. Eight species were detected using the fishway, of which five were native (Liza ramada, Anguilla anguilla, Barbus graellsii, Gobio lozanoi and Salaria fluviatilis) and three exotic (Alburnus alburnus, Cyprinus catpio and Rutilus rutilus). Only L. ramada used the fishway in substantial numbers. The rate of fish passage was the highest from June to August and decreased afterwards. The effectiveness of the fishway might be lowered by amas of turbulence within the fishway and by distraction flows from a nearby hydropower station.