| Abstract |
The study carried out in 2016 is about the evaluation of present and future Clain’s potentiality for migratory fish, more particularly Shad and Lamprey. The surface of running areas is about 14 ha and this is 6 % of the total area of water. This value is due to the type of river (lowland river with a low pitch), and to the existence of 39 dams. However, the Clain has a non-negligible capacity for Lampreys. The area of potential spawning grounds is between 4.0 and 8.7 ha, which represents between 60 000 and 130 000 spawners. However we observed 0.5 ha of potential spawning grounds for Shad only downstream. This result is coherent with the fact that the Shad have a preference for watercourse larger than 30 m. Adjusting or erasing these dams is necessary for re-opening the watercourse to the migratory fishes. Indeed, the bathymetry study shows the potentiality of this watercourse if works on the dams were started. Erasing the Moulin de la Grève and the Moulin du Clain would create 1 277 m2 of potential spawning grounds for Lamprey. |