Behaviour and passage of European silver eels (Anguilla anguilla) at a small hydropower plant during their downstream migration

Abstract

Key-words:silver eel, downstream migration, behaviour, hydroelectric plant, trashracks, radio-tracking Between 2004 and 2007, 116 downstream migrant silver eels (Anguilla anguilla) were monitored at a hydropower plant on the Gave de Pau river in South-West France using radio and PIT telemetry. The objectives of the study were: (i) to determine the environmental conditions when eels arrived and passed the facility; (ii) to determine the rate of eel escapement (passage other than via the turbines); (iii) to describe the behaviour of eels faced with the intake structure and the permeability of the intake trashracks for the different sizes of eel; and (iv) to determine whether surface bypasses originally designed for salmon could be effective for eels. Five types of behaviour of silver eels in the forebay and at the plant intakes were identified. The study showed the key factor influencing both eel behaviour and the route taken through the plant was variation in river discharge. Escapement rate was related to eel length and the spill flow to river flow ratio, which could be described by a logistic regression model. The surface bypasses originally designed for salmon were found to aid downstream eel migration significantly. At velocities < 0.40 m·s −1 , no eels, even the largest, for which the racks are a physical barrier, were found impinged on the trashracks.

Impact of Tide Gates on the Migration of Adult European Eels, Anguilla anguilla

“…sluices, flap gates, and bypasses) subsequently passed via these structures (Travade et al 2010). Travade et al (2010) and others (e.g. Breteler et al 2007;Jansen et al 2007) suggest that eels tend to escape via the route of dominant flow, an observation supported by the current study in which most eels (75.9%) exited through Gate 1 which discharged the highest volume.…”

“…Conversely, at the Baigts hydroelectric facility in the Gave de Pau river (France), 76% of downstream moving radio and PIT tagged silver eels that explored alternate routes to the turbines (e.g. sluices, flap gates, and bypasses) subsequently passed via these structures (Travade et al 2010). Travade et al (2010) and others (e.g.…”

“…While tide gates physically block migrating fish when closed, the narrow apertures through which water is discharged when open, and culvert entrances, may create a hydrodynamic barrier in the form of a rapid acceleration of flow which acts as a repellent (Pacific salmonid smolts: Enders et al 2009;Kemp et al 2005b, silver European eels: Piper et al in prep.). Indeed, eels have been observed to exhibit non-passive exploratory behaviour at other riverine structures (silver American eels, Anguilla rostrata: Brown et al 2009;Castro-Santos 2000, silver European eels: Behrmann-Godel andEckmann 2003;Travade et al 2010) during which they may reject an area approached, to either approach again, or find an alternative route (e.g. Brown et al 2009).…”

Characterization of the Water Quality Status on a Stretch of River Lérez around a Small Hydroelectric Power Station

“…This ladder, if used, would reduce the negative impact of the dam on the fish population [11], but we registered no use of this ladder and consequently a probable effect of the dam on the fish population. Diversion dams of SHP plant hinder the passage of eels [47,48]), and also alter the populations of other fish species [41,46,49]. Some authors [41,46] found differences in population size-structure among sites upstream and downstream from SHPs with suitable fish passes for Barbus bocagei and Squalius carolitertii, as well as for B.bocagei, S. carolitertii and Salmo trutta in SHPs with unsuitable fish passes.…”

What are the consequences of fish entrainment and impingement associated with hydroelectric dams on fish productivity? A systematic review protocol

“…Minimal research exists on downstream passage and entrainment risk of resident fish species [8]. However, research on adult downstream passage in migratory fish is growing in popularity in temperate Europe and North America, particularly for species of conservation interest such as eels (Anguilla spp., [14][15][16][17][18][19]) and sturgeons (Acipenser spp., [20][21][22]). To enhance downstream passage and reduce mortality, management strategies have included selectively timing spills to aid juvenile fish, the installation of "fish friendly" by-pass systems and screens directing fish to these systems, and retrofitting dams with low-volume surface flow given differences in: (1) site-specific factors (e.g., turbine type, size, power output); (2) methodologies and study designs used to assess impacts; and (3) biological factors (e.g., fish life history stage, body size and morphology).…”