Analyse des pratiques, contraintes et performances d'élevage de l'huître creuse Crassostrea gigas, en 2001, sur différentes concessions en eau profonde de la Baie de Quiberon : enquête auprès de 18 concessionnaires et plongées sur 18 semis d'huîtres de 2 ans, en juin et octobre 2001

This study deals with rearing methods, growth and mortality performances, and problems encountered by the oyster farmers from Quiberon Bay (2800 ha of leases) : it relies on a survey achieved in july 2001, about 18 oyster farmers, and 2 diving campaigns (july and october 2001) on 2 years old oyster batches from the same farmers. The analysed enterprises vary in particular by the location and depth of their concession inside the bay, but also by their rearing scheme : a majority favours seedings with 18 month old oysters or more, according to prices and availability of oysters supplies. The duration until marketable size and mean mortalities seem to have increased since a preceding inquiry in 1986. The main constraint, affecting priorly the south border parks, expoded to the open sea, occurs from starfish (Asterias rubensin peculiar). Benthic red algae are also a nuisance to exploitation and eventually to oysters themselves, when they accumulate in thick layers. The main concern declared by the farmers is mortality rates, both at spat stage and commercial size. Difficulties have emerged from the variability in practices and bottom situations, but references have been acquired that may be used in ecosystem studies or long run monitoring of the area.