The effect of ramp slope and surface type on the climbing success of shortfin eel (Anguilla australis) elvers

Abstract

Instream structures such as dams, weirs and culverts reduce diadromous fish (e.g. freshwater eels) biodiversity and abundance by restricting upstream migrations. Fish passes are used to facilitate fish passage around instream structures, but limited information is available about design aspects that influence the ability of fish to negotiate the structures. We used experimental ramps to evaluate the effects of surface type and slope on the climbing success of shortfin eel (Anguilla australis) elvers (total length <155mm). Climbing success was examined for three surface types (smooth plastic, sand and gravel, Miradrain) at slopes of 30, 50 and 70°. Elver climbing ability differed among substrates, with the highest success observed on the Miradrain surface (a moulded plastic drainage product). Climbing success decreased with increasing ramp slope. The mean length of elvers successfully negotiating the ramps was longer than that of elvers that failed to climb because only larger elvers could climb the Miradrain surface as ramp slope increased. Results indicated that the optimal ramp-designed passage for climbing species would be lined with Miradrain and set at an angle close to 30° and not exceeding 50°. Elver passage will be detrimentally affected by steep surfaces, which will be exacerbated if suboptimal ramp-surface types are used.

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.…”

“…Birnie-Gauvin et al, 2018). Experimental studies on the passage of juvenile eels show that small modifications in ramp design or properties, such as hydraulics, type of attraction flow, substrate type, slope, and placement can create dramatic changes in passage efficiency (Drouineau et al, 2015;Jellyman, Bauld, & Crow, 2017;Piper, Wright, & Kemp, 2012), and omitting evaluations will contribute to the continued operation of measures with suboptimal FPS efficiency (Birnie-Gauvin et al, 2018).…”

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

“…Upstream passage solutions for juvenile eels instead take advantage of the eels’ rheotactic and thigmotactic climbing behaviour (Jellyman, ; Geffroy & Bardonnet, ) and generally consist of an inclined ramp lined with a wetted climbing substratum (Solomon & Beach, ) with an attraction flow at the entrance of the ramp (Piper, Wright & Kemp, ). The features of the ramps, such as climbing substratum and slope, are critical, as the efficiency in aiding the ascent of juvenile eels (both in terms of passage success rate and climbing velocity) may directly affect the performance of the passage solution (Jellyman et al ., ; Anwar, ). Evaluations of single substrata have shown that, for example studded plastic tiles and bristle passes improve passage success at Crump weirs (Kerr et al ., ; Vowles et al ., , ), but few studies have directly compared the performance of different climbing substrata (Jellyman et al ., ).…”

“…The features of the ramps, such as climbing substratum and slope, are critical, as the efficiency in aiding the ascent of juvenile eels (both in terms of passage success rate and climbing velocity) may directly affect the performance of the passage solution (Jellyman et al ., ; Anwar, ). Evaluations of single substrata have shown that, for example studded plastic tiles and bristle passes improve passage success at Crump weirs (Kerr et al ., ; Vowles et al ., , ), but few studies have directly compared the performance of different climbing substrata (Jellyman et al ., ). A recent study by Tamario et al .…”

“…At present, the alarmingly low densities of upstream‐migrating juvenile eels suggest that immediate actions are required to increase the proportion of eels passing upstream migration barriers. During recent years, several new upstream passage solutions have been developed, but research assessing the performance of these solutions has until recently been completely lacking, and only a handful of studies address this issue (Kerr, Karageorgopoulos & Kemp, ; Vowles et al ., , ; Jellyman, Bauld & Crow, ). In particular, further studies evaluating the effects of upstream passage solution design and placement are needed.…”