The potential of lateral refuges for Iberian barbel under simulated hydropeaking conditions

Abstract

Fish responses to hydropeaking may range from sub-organismal adjustments to key life-event changes. It is currently difficult to quantify these responses and to assess the potential of artificial refuges accordingly. To address this problem, two experimental trials were conducted in an indoor flume. In the first, two hydropeaking events were tested in the presence of deflectors as flow refuges. In the second, the presence and absence of deflectors was tested for the same hydropeaking event. A multidisciplinary approach combined physiological and movement behaviour responses of Iberian barbel (Luciobarbus bocagei) with hydrodynamic models. These were used as a complementary tool to explain the fish responses. In the first experiment, no evident physiological adjustments occurred. However, individual refuge use and swimming activity were higher in the single-step event where velocities above 0.6 m.s−1 were observed. In the second experiment, the levels of glucose were the highest in the repeated single-step event with deflectors, whereas in their absence no visible changes were observed. The sequence of discharges affected the frequency of individual sprints and group drifts, particularly evident with deflectors. Additionally, the deflector use increased in the first peak in opposition to the second. Overall, the fish responses were indicative that the low velocity areas (<0.1 m.s−1) existing behind the deflectors were favourable under hydropeaking conditions. However, the flow complexity resulting from the presence of deflectors impaired their ability to successfully find them. The integrated approach used in this study provided novel insight considering the responses of cyprinids to hydropeaking in the presence and absence of deflectors as a mitigation measure. This study emphasized the importance of characterizing the hydrodynamic conditions due to hydropeaking, particularly after including the artificial refuges.