Study of the feeding habits of the Brent Goose in the Saint Brieuc Bay National Nature Reserve

The Saint Brieuc Bay National Nature Reserve, located in the north of Brittany, is winter migration site of international importance for the dark-bellied Brent Goose Branta bernicla bernicla, despite the total absence of its favourite food, eel grass. Monitoring has revealed that Ulves Ulva armocicana represents 90% of the sustenance locally ingested by Brent Geese. This ulvaceae is responsible for spectacular green tides which have a great impact on the bay each summer. Each year Brent Geese consume 400 tonnes, but nevertheless does not stem the phenomenon. However, the reabsorbtion policy for excess nitrates which are coming into effect in the bay could, in time, reduce this food source and mean the geese would need to find an alternative food source. Here in the bay, this could be a grass which grows in the salt marshes (Puccinellia maritima), or winter cereals planted in the fields bordering the bay. In order to avoid potential crop damage, the reserve may need to enlarge the existing Puccinellia maritima salt marshes, either by mowing or by cultivating pastures of Halimione portulacoides in climacic areas, as is the case in Aiguillon Bay. This will have to be done with caution, the areas with sea-purslanes being important feeding grounds for young fish during high tides. It is clear that, in this bay, a wintering area of international interest for a particular species of water bird has developed thanks to serious environmental imbalance. It is therefore possible that this ornithological interest could be disrupted by current curative water quality restoration policies, should no compensatory measures arise to compensate for the planned reduction of the green tide.