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The Bay of Brest and its catchment areas


The maritime basin of the Bay of Brest spans an area of nearly 180 km², with an average depth of 8 meters. To the west, the bay is limited by the Marine Park and to the east by the salt/fresh water border in the estuaries of the River Elorn at Landerneau and of the River Aulne at the lock in Port-Launay, downstream of Châteaulin. The study area includes also the intertidal zones and the catchment areas of the rivers and streams flowing into the bay, of which those of the Elorn (280 km²) and the Aulne (1,822 km²) are the main ones.


Two catchment areas with unequal population distributions

Although the catchment area of the Elorn is smaller than that of the Aulne, it has a larger population (285,000 inhabitants) which is unevenly distributed, with high densities around Brest, Landerneau, and Landivisiau.

The population of the catchment area of the Aulne is lower (70,000 inhabitants) and is distributed more evenly. A total of 121 municipalities, large and small, and grouped into 19 `communities of municipalities', share the territory of these two catchment areas.


A rich and diverse ecosystem

The ecosystem of the Bay of Brest is rich and diverse in terms of habitat, flora and fauna (listed in the REBENT database). The estuarine areas are breeding grounds and nursery areas for many species. The ecosystem of the Bay of Brest is also of great importance for human activities, both commercial (fishing, shellfish aquaculture, tourism, ...) and recreational (fishing, boating, water sports, ...).