Session B7: On the Performance of a New Upstream and Downstream Passage Facility for Diadromous Fish Species

Abstract: The River Ätran is an important river for diadromous fish species on the Swedish westcoast. Wild populations of wild Atlantic salmon, brown trout, European eel and sea lamprey enter the river for spawning and growth. The conditions for migratory fish species are improving in the river since rehabilitation efforts now address the needs of all diadromous species and life-stages, and not only upstream moving salmonids. This presentation presents results from before and after the construction of a new two-way passage facility at the Herting hydroelectric plant (HEP) near the river mouth. The old facility consisted of a Denil fishway for upstream passage and spill gates for downstream passage. The total passage efficiencies (TPE) differed among species and life-stages, with 70-90% being recorded for salmon spawners, smolts and kelts. The corresponding TPE for juvenile eels was 10- 50%, 70% for silver eels and 0% for sea lamprey spawners. The new facility consists of a large naturelike fishway for upstream passage and a low-sloping 30˚ β-rack and a full-depth bypass for downstream passage. Evaluation of the new facility is in progress, and preliminary results indicate a high passage survival of about 90% for salmon smolts and spawners. Most silver eels managed to pass successfully (97%), but the HEP was only operating for part of the study period; TPE for silver eels and sea lamprey will be evaluated during 2015