Can vegetation provide shelter to cyprinid species under hydropeaking?

A novel study that focuses on the capacity of vegetation to provide shelter for fish species under hydropeaking regimes is presented. Two artificial patches mimicking the structure and density of Carex sp. mats were installed in an experimental flume to test whether submerged plants can offer flow refuge to two cyprinid species, Luciobarbus bocagei and Pseudochondrostoma polylepis, under baseflow and hydropeaking scenarios. Local flow fields were characterized using a Lateral Line Probe (LLP) and an Acoustic Doppler Velocimeter (ADV) and 33 h of video analysis were viewed to report, on a per-second basis, fish use of 1) patches with plants, 2) patches upstream and 3) downstream from vegetation and 4) patches without vegetation. Data on flow fields and fish patch use were integrated and analyzed to assess whether plants favored fish sheltering behavior. Vegetation created hydraulically stable areas suitable for fish to shelter, triggering changes in fish patch use. Although both species sheltered under hydropeaking, L. bocagei presented a stronger preference than P. polylepis for vegetated patches and areas downstream from plants, taking advantage of sheltered regions more frequently. P. polylepis weaker search for shelter could be related to species-specific factors and territorial behavior interferences rather than to fish performance relative to flume hydraulic conditions. Despite a weaker response, some P. polylepis individuals used patches downstream from plants more during the second half of the hydropeaking trials. A trade-off between reducing swimming effort and territoriality might explain this response. Results indicate that vegetation can help to counterbalance the impact of hydropeaking on fish while providing river functioning benefits. Evaluating fish sheltering to a wide set of river plants and patch designs on a species-by-species basis would help targeting vegetation-based actions for restoring hydropeaking rivers.