Downstream migration and hydropower dam passage of a Danubian cyprinid, Rutilus meidingeri, at the Seeache River, Austria

Abstract

Downstream passage at a hydroelectric power plant of pearlfish (Rutilus meidingeri), a cyprinid species endemic to the Danube catchment, was examined. Forty pearlfish were trapped in the fish pass during their upstream migration, tagged with telemetry transmitters and subsequently released to the upstream section of the weir. The tagged fish were monitored to determine their descending behaviour and ability to overcome the obstacle through three possible corridors: a bypass channel, the overflown weir, and a vertical slot fish pass. Pearlfish used the entire 2.7 km of the river by successfully migrating further upstream and also by descending past the obstacle back to Lake Attersee through the bypass channel (65 %), and the weir overflow (35 %). No fish utilised the fish ladder as a descent corridor, even though 82 % of the fish were registered in the vicinity of the entrance to the facility. Apart from the unfavourable positioning of the fish pass for downstream migration, the discharge conditions proved to be decisive for the choice and availability of the descent corridor as well as the behaviour during descent. Significant delays in power plant passage occur both in the forebay and at the used corridors. Even if the ability to find corridors and the passability of adult pearlfish can be proven, further measures appear to be necessary for the safe migration and protection of the endangered species.