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

J Watz,O Calles,P A Nilsson,C Tamario,E Degerman

doi:10.1111/acv.12485

Abstract

AbstractConservation 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.

Highlights

The ultimate goal of the management of endangered species is for them to become self-sustaining elements in their natural ecosystems (Tear et al, 1993)
There was a significant effect of substratum on the mean number of approaches, and the studded substratum attracted more approaches than the bristle substratum, but not significantly more than the open weave (Fig. 5; Bonferroni post-hoc pairwise comparisons Pstudded vs bristle = 0.04, Pstudded vs open weave = 0.40, Popen weave vs bristle = 0.55)
More eels initiated a climb in the studded substratum than in the open weave and in the bristle substrata

Summary

Introduction

The ultimate goal of the management of endangered species is for them to become self-sustaining elements in their natural ecosystems (Tear et al, 1993). While there is a general positive relationship between funding for conservation projects and successful recovery (Gerber, 2016), decisions made by managers on how to spend this funding can have major effects on the probability of success. These decisions are, often made without consulting evidence or under uncertainty, resulting in potentially cost ineffective species conservation practices (Sutherland et al, 2004; Milner-Gulland & Shea, 2017). Conservation actions need to target the most critical life stage for population growth. Animal Conservation published by John Wiley & Sons Ltd on behalf of Zoological Society of London. 1

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Conclusion