Cover or Velocity: What Triggers Iberian Barbel (Luciobarbus Bocagei) Refuge Selection under Experimental Hydropeaking Conditions?

Miguel Moreira,Isabel Boavida,Maria João Costa,Jorge Valbuena-Castro,António N Pinheiro

doi:10.3390/w12020317

Abstract

The rapid river flow variations due to hydropower production during peak demand periods, known as hydropeaking, causes several ecological impacts. In this study, we assessed the potential of an overhead cover and velocity-refuge structure in an indoor flume as an indirect hydropeaking mitigation measure for the cyprinid species Iberian barbel (Luciobarbus bocagei). We designed a lab-scale LUNKERS-type structure using two different materials which were used separately: Wood (opaque) and acrylic (transparent), tested under hydropeaking and base-flow events. Physiological (glucose and lactate) and behavioral (structure use) responses were quantified. The structure use (inside and in the vicinity) and the individual and schooling behavior was assessed. Although there was no evidence that the hydropeaking event triggered a physiological response, the wood structure use was significantly higher than the acrylic one, where the metrics of use increased in the hydropeaking event. Differences between individual and group behavior were only higher for the entrances in the wood structure. The higher frequency of wood structure use under hydropeaking conditions suggests that the visual stimulus conferred by this shaded refuge enables fish to easily find it. The results suggest that the use of overhead and velocity-refuge structures may act as an effective hydropeaking flow-refuge mitigation measure.

Highlights

The operation of storage hydropower plants generally causes rapid and artificial flow fluctuations, due to turbines that are started up and shutdown according to the demand of the electricity market, often on daily or sub-daily time scales
We addressed the following questions: (1) Are the blood lactate and glucose levels of L. bocagei altered under hydropeaking conditions in the presence of LUNKERS-type structures? (2) Does L. bocagei use the structures as areas of reduced flows under hydropeaking conditions? (3) Is the visual stimulus critical to fish that use the structures as a refuge under rapid flow fluctuations?
We considered a single structure use when one fish used the L-structure isolated from the group, whereas group behavior was considered when two to five fish used the structure as a school

Summary

Introduction

The operation of storage hydropower plants generally causes rapid and artificial flow fluctuations, due to turbines that are started up and shutdown according to the demand of the electricity market, often on daily or sub-daily time scales This operation mode—called ‘hydropeaking’ [1], leads to rapid increases or decreases of river discharges, altering the velocity and water depth at the tailrace. In rivers affected by hydropeaking, hydromorphological characteristics may be significantly altered, including, e.g., substrate composition, banks wetted width and habitat suitability [3,4,5], with negative consequences for fish species, such as, e.g., stranding, dewatering of spawning grounds, and downstream displacement [6,7,8,9] Those impacts are site-specific and, mitigation measures should be adapted considering the river morphology together with species–specific ecological requirements [6]. Hydropeaking mitigation measures can be grouped into direct and indirect

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