Fish under pressure: Examining behavioural responses of Iberian barbel under simulated hydropeaking with instream structures

Abstract

Hydropeaking is the rapid change in the water flow downstream of a hydropower plant, driven by changes in daily electricity demand. These fluctuations may produce negative effects in freshwater fish. To minimize these impacts, previous studies have proposed habitat enhancement structures as potential mitigation measures for salmonids. However, the recommendation of these mitigation measures for cyprinids remains scarce and their effects unknown. In this study, the effects of potential habitat mitigation structures under simulated hydropeaking and base-flow conditions are examined for Iberian barbel (Luciobarbus bocagei) in an indoor flume. Solid triangular pyramids and v-shaped structures were evaluated as potential flow-refuging areas and compared with a configuration without structures. A novel, interdisciplinary approach is applied to investigate individual and group responses to rapidly changing flows, by assessing physiological (glucose and lactate), movement behaviour (structure use, sprints and drifts) and the pressure distribution using a fish-inspired artificial lateral line flow sensor. The major findings of this study are four-fold: 1) Under hydropeaking conditions, the v-shaped structures triggered a lactate response and stimulated individual structure use, whereas solid structures did not elicit physiological adjustments and favoured individual and group structure use. Overall, both solid structures and their absence stimulated sprints and drifts. 2) The hydrodynamic conditions created in hydropeaking did not always reflect increased physiological responses or swimming activity. 3) Each event-structure combination resulted in unique hydrodynamic conditions which were reflected in the different fish responses. 4) The most relevant flow variable measured was the pressure asymmetry, which is caused by the vortex size and shedding frequency of the structures. Considering the non-uniform nature of hydropeaking events, and the observation that the fish responded differently to specific flow event-structure combinations, a diverse set of instream structures should be considered for habitat-based hydropeaking mitigation measures for Iberian barbel.

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

“…Group disruption was particularly marked in the entrances frequency (IL) in the LW hydropeaking experiments (LWHP), where the statistical analysis resulted in significant differences between IL_G and IL_I. Similar results were obtained by Costa et al [16,25,32], where authors observed an increase of schooling disruption with the peak discharge. The advantages of schooling behavior have been demonstrated to reduce the total swimming costs [22,66], including during reproductive migrations [67,68].…”

“…Authors assumed it was a behavior to avoid displacement during artificial high flow events, where fish could use solid substratum and marginal cover as velocity-refuge areas, which is in line with our results. Increases in behavioral metrics associated with peak discharges have also been reported in indoor and outdoor experimental flumes (e.g., [14,16,25,32,59]), as well as in rivers affected by hydropeaking (e.g., [60][61][62][63]).…”

“…Each school was tested only once. The selected number of replicates and group size is currently accepted for this type of research (e.g., [16,25,32,[42][43][44][45]). Larger schools of L. bocagei likely occur in nature.…”

“…Therefore, it is expected that physiological responses under hydropeaking conditions will be higher than those in base-flow conditions, though the direction and range of those responses is difficult to determine [24]. Recent studies demonstrated that hydropeaking triggers distinct physiological and behavioral responses, according to the combination of hydrodynamic conditions with the presence of lateral and instream structures (e.g., [16,25]). However, the potential of overhead cover and velocity-refuge structures to trigger physiological changes under similar conditions has not yet been tested.…”

“…The study was carried out in an indoor flume, where we analyzed physiological and behavioural responses of the Iberian barbel species (Luciobarbus bocagei, Steindachner 1864). Young adults of L. bocagei were used for this study, as they are adapted to faster flow conditions, demonstrated to favor rheotactic behavior [25,32]. Thus, by subjecting fish to a hydropeaking event in the presence of structures that provide different hydraulic (base-flow vs. hydropeaking) and visual (opaque vs. transparent) stimuli, our objective was to determine whether it was critical for L. bocagei to use the structure as a flow-refuging area.…”