Climbing the ladder: an evaluation of three different anguillid eel climbing substrata and placement of upstream passage solutions at migration barriers

Abstract

Conservation programmes for endangered, long-lived and migratory species often have to target multiple life stages. The bottlenecks associated with the survival of juvenile anguillid eels migrating into inland waters, the survival and growth of the freshwater life stage, as well as the recruitment and survival of silver eels, migrating back to the ocean to spawn, must be resolved. In this study, we focus on the efficiency of passage solutions for upstream-migrating juveniles. Such solutions can consist of inclined ramps lined with wetted climbing substrata. We evaluated different commonly used substrata in a controlled experiment, recorded eel behaviour at the entrance of the ramp with infrared videography and validated the experimental results at a hydropower dam, where we also investigated the effects of ramp placement on performance. In the experiment on eel substratum selection, 40% of the eels passed in lanes with studded substratum, whereas only 21 and 5% passed using open weave and bristle substrata respectively. Video analysis revealed that the studded substratum attracted more approaches and initiated climbs than the other substrata, but once a climb had been initiated, passage success rates did not differ between substrata. Eels using the studded substratum climbed 26% faster than those using the bristle substratum and almost four times as fast as those climbing in the open weave. The superior performance of the studded substratum was supported by data from the field validation. Moreover, ramps positioned by the bank with low water velocities caught the most eels, but proximity to the dam had no effect on performance. To strengthen the European eel population, more juveniles need to reach their freshwater feeding grounds. A critical step to achieve this increase is to equip upstream passage solutions with suitable substrata and to optimize ramp placement at migration obstacles.

Coastal river connectivity and the distribution of ascending juvenile European eel (Anguilla anguilla L.): Implications for conservation strategies regarding fish‐passage solutions

“…Despite the results presented here, indicating a low efficiency of eel ramps in facilitating upstream migration, the literature contains several reports of efficient implementations (Briand et al, ; Knights & White, ; Legault, ; Solomon & Beach, ). Studies also show that manipulating certain design features can have fundamental impacts on the success of eel ramps (Anwar, ; Drouineau et al, ; Jellyman et al, ; Kerr et al, ; Piper et al, ; Watz, Nilsson, Degerman, Tamario, & Calles, ). This knowledge needs to be transformed, however, into conservation action.…”

“…Water temperature influences the composition of riverine species and their respective catchability using electrofishing by wading, as, for instance, diel or seasonal swimming activity and migration patterns are affected by temperature (e.g. Trigal & Degerman, 2015). Moreover, for eels, temperature has been shown to be an important correlate for initiation of elver and juvenile migration (White & Knights, 1997), and has a large impact on swimming and climbing activity and behaviour (Linton, Jónsson, & Noakes, 2007).…”

Occurrence and habitat use of European eel (Anguilla anguilla) in running waters: lessons for improved monitoring, habitat restoration and stocking

“…overexploitation (Moriarty and Dekker 1997;Jacoby et al 2015), ocean climate change (Castonguay et al 1994;Durif et al 2011), pollutants (Feunteun 2002) and the effect of parasites (Sjöberg et al 2009). In freshwater, the main causes of the decline are suggested to be poor function and placement of passes for eel immigrating to freshwater (Tamario et al 2019;Watz et al 2019), loss and deterioration of freshwater habitat (Feunteun 2002) and delay and mortality of maturing eel passing dams and power plants (Besson et al 2016).…”

Hydraulic management of coastal freshwater marsh to conciliate local water needs and fish passage

“…Currently the most usual solution for glass eel passage at physical obstacles consists of climbing ramps (Porcher 2002). Their efficiency mainly depends on the type of substrate used (Watz et al 2019), the water temperature (Linton et al 2007), the hydraulic conditions on the ramp, and the attraction flow rate (Piper et al 2012).…”