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    matthieu.chanseau@onema.fr

A study on the impact of structures in the Adour river basin

In the Aquitaine region, Onema recently studied the impact of structures on all migratory species, in terms of both upstream and downstream migrations.

In the Aquitaine region, Onema recently studied the impact of structures on all migratory species, in terms of both upstream and downstream migrations. The study dealt with eight rivers and torrents in the Adour basin. From the fall of 2008 to the summer of 2009, Onema personnel from the Sud-Ouest regional office and the Pyrénées-atlantiques local office examined 91 obstacles where biological issues are a major concern. The assessment was based on hydrological field data and on analysis calling on in-depth knowledge of the behaviour of migratory fish and the impact of each structure (radio telemetry, biological monitoring, etc.). By combining the data on biological issues, structure "passibility" and the geographical position of each structure on migratory routes, the study revealed that 13 structures have a major impact on upstream migration, 39 have a medium to strong impact and another 39 have a low to zero impact. Following this initial diagnosis, 86 improvement suggestions were examined and ranked according to three priority levels. The top priority level included ten new fishways, modifications on ten existing fishways, increases in environmental flow rates for 12 short-circuited sections and the elimination of three obstacles that no longer serve any purpose. It is now necessary to discuss the study results with all the concerned partners and to jointly establish plans to improve the migration of fish in the Adour basin.

 

CONTACT: matthieu.chanseau@onema.fr

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