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Ecosystem management of coastal marshes

In 2006, a partnership between the town of Braud-et-Saint-Louis, ONCFS and Onema was set up at the Terres d’oiseaux ornithological park. The goal was to experiment new management techniques designed to improve environmental operation for fish species, notably eels, while taking fully into account the other site requirements.

Terres d’oiseaux is located on the right bank of the Gironde estuary, in the heart of the Blayais coastal marshes. With a central canal connected to the estuary and eight lakes, the site is a favourable environment for Anguilla anguilla, the European eel. Following a series of degradations, the town of Braud-et-Saint-Louis called on ONCFS (national agency for hunting and wildlife) to restore terrestrial biodiversity and improve habitats. ONCFS redesigned the hydraulic network to create the lakes and ensure connections both between the various compartments and with the estuary. The eel mortalities noted during the summer of 2006 led ONCFS to bring in the Onema South-west regional office in order to better take into account the aquatic environment and establish a new hydraulic management system for the site.

An ecosystemic approach

From the start, an ecosystemic approach addressing all the issues and constraints noted on the site was adopted. The hydraulic operation of the site was the central issue. The goal was to recreate frequent interaction with the estuary waters. A satisfactory solution was found requiring modification of a single installation that controls entry of water from the estuary and maintains a minimum water level on the site.

The site is now continuously connected to the estuary and operates in step with the tides, except during spring tides when it is cut off to prevent flooding. From May to September, when many birds nest on the site, entry of water is limited to avoid excessively raising the water level, while maintaining favourable conditions for fish. Fishing expeditions were launched at intervals to determine the initial population levels of fish and the effectiveness of the new measures implemented starting in the fall of 2010. The latest expedition during the fall of 2011 by the special migratory-fish unit of the Onema Adour-Garonne office revealed positive changes in fish populations and the appearance of new species, such as the meagre. This promising approach is now being used on other sites managed by ONCFS and other partners.

Contact : matthieu.chanseau@onema.fr