Session A6: Fish Behaviour Analysis in a Vertical Slot Fishway

Abstract: The improvement of devices that allow the upstream and downstream migration of fish through hydraulic constructions in rivers is nowadays a real priority to maintain the continuity of the biodiversity. Among lot of constructions, the vertical slot fishways (VSF) are commonly used and are effective in ensuring unhindered passage of the large sizes fish. A typical problem is that, first, fishes have to find the entrance of the fishway and, when they have found it, small sized fish can encountered difficulties to progress due to the inappropriate flow conditions. This comment is highly linked to the fish locomotion modes that depend to the species in regard with turbulence (kinetic energy, Reynolds stresses, vorticity, strain, eddy length scales) and the instantaneous flow features. In general, fish tend to avoid flows that have unpredictable, wide fluctuations in velocity that interfer with swimming trajectories. Unfortunately, those conditions based on fish swimming capabilities could not be anticipated by the commonly-used criteria to design VSF. At consequence, a better understanding of the relationship between fish swimming behaviour and accurate hydraulic conditions in a VSF is necessary. This study investigated the swimming behaviour of small-sized chubs, (8 ≤ TL \u3c 12 cm), under experimental VSFs flow conditions. All the fish movements between pools were video-recorded and analyse with view point of fish movements between pools, stabling zones, transit time and trajectories. Flow turbulence and instantaneous evolution of the flow were analysed using PIV and ADV datas and were related with fish swimming behaviour. The influence of turbulence on the swimming behaviour was assessed for original VSFs and modified VSFs by addition of one or three cylinders. The results show that flow in existing vertical slot fishways can be adapted with the addition of vertical cylinders inside each pool