Survey of downstream migration of silver eels through discharge pipe on a reservoir dam

The survey of the catadromous migration of eels through a major dam was operated on a pipe insuring a minimal legal discharge of the dam of Bois Joli on the Fremur River (Northern Brittany, France : height, 13.7 m; Volume, 3 Millions of m(3)). Part of the silver eels used this pipe to emigrate, at the beginning of the downstream run when it represented the only possible downstream passage, but also later when the dam spill enabled a second emigration pathway. Because of the low discharge and of the design of the pipe, it is assumed that eels look for a possible seawards passage.