Success of a low-sloping rack for improving downstream passage of silver eels at a hydroelectric plant

• 1. The European eel (Anguilla anguilla) is a critically endangered species, and one major threat is thesurvival of silver eels migrating downstream towards the sea from lake and river rearing areas. Duringthis migration, many eels are impinged and die on intake racks, or are injured or killed whenpassing through turbines.2. Intake racks at a hydroelectric plant were modified to avoid impingement and to collect eels withoutinjury; high mortality on both racks and in turbines was previously documented. Modificationsconsisted of reducing the rack gap width from 20 to 18 mm, decreasing the rack slope from 63 to 35degrees, increasing the rack surface area by 58% and installing six openings in the rack leading totraps.3. Downstream passage conditions for silver eels at the hydroelectric plant were significantlyimproved, reducing mortality from >70% at the old steep 20 mm racks to <10% at the modified18 mm rack collection facility. No tagged eels were impinged and killed on the racks, and 80%entered the collection facility.4. Survival can probably be improved even more, as the individuals that passed the facility mostlikely escaped through holes in the traps. Moreover, injured untagged eels were still encountered atthe modified racks, illustrating the need for rehabilitative measures to be implemented at all obstaclesbetween the main eel rearing areas and the sea.

Subject headings

TEKNIK OCH TEKNOLOGIER  -- Naturresursteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Environmental Engineering (hsv//eng)

Keyword

Biology

Biologi

Publication and Content Type

ref (subject category)

art (subject category)