Bilan du suivi de l'exploitation industrielle de la crépidule en Bretagne Nord (baies de Saint-Brieuc et du Mont Saint-Michel) 2002-2005

The slipper-limpet (Crepidula fornicata) is a marine gastropod which causes serious perturbations in shellfish beds, because of spatial spreading and density rising. Along French coasts, in Northern Brittany, two bays are highly colonized : bay of Saint-Brieuc, centre for scallops fishery, and bay of Mont-Saint-Michel, a famous oyster-farming area, with a total limpet stock about 450 000 metric tons. The association AREVAL was founded in 2001 to manage there, an industrial collect of limpets by a succing-dredge, followed ashore by a treatment for calcareous soil improvement. The scientific survey, contracted to IFREMER, included measurements of long andshort-term dredge's effects on grounds and limpet population, and proposals to set up dredging management. The survey has focused on bay of Saint-Brieuc, instead of bay of Mont-Saint-Michel where collect is limited to dumping grounds for oyster–waste. Annual cruises for survey brought in operation observation systems such as side-scan-sonar and underwater video, and sampling operations by divers and grabs. A four year survey is here reported. Thanks to present results and previous data concerning the spreading strategy, several advices are given for dredging management in shellfisheries.