Endurcissement du naissain d’huîtres creuses, Crassostrea gigas par le niveau d’exondation ou la densité d’élevage : récapitulatif d’essais conduits entre 2004 et 2007 en rivière d’Auray (56), pour réduire les mortalités estivales

This report summarizes a list of husbandry experiments conducted between 2004 and 2007 so as to reduce the summer mortalities of the oyster Crassostrea gigas by farming practices. The Japanese technique so‐called “hardening”, based on nursing the young oysters (less than 1 year‐old) in intertidal areas with high air exposure, is tested and adapted. Significant improvements of survival rates (e.g. 60% survival instead of 40% survival rate) have been obtained by transferring the spat only a few month (between march and june‐july) on “high” inter‐tidal farming plots (up to 40% of mean air exposure time). In such conditions, growth is transiently reduced, but a compensatory growth seems to happen when oysters are transferred back on low concessions. Another means of reducing growth, by increasing the density of oysters per bag, was not successful in terms of survival. The physiological effect induced by “hardening” oysters remain to be cleared and the technique tested in other sites before large scale application. Its benefit needs also to be tested in the new context of epidemic disease striking oyster cultures in France, since 2008.