Mortalité de l'huître Crassostrea gigas dans le bassin de Marennes-Oléron: étude de la variabilité spatiale de son environnement et de sa biologie par un système d'informations géographiques (SIG)

The summer mortality patterns was studied in 1996 on the Ronce-les-Bains oyster bank (175 ha), located on the southern part of the Bay Marennes-Oleron (Atlantic coastline). Studies on growth, sexual maturation, survival rates and environmental variables were compared at fifteen experimental sites (on- and off-bottom culture). After 7 months, cumulative mortality reached 8-19 and 23-33% for off-bottom and on-bottom culture, respectively which is significantly higher for the latter case. A seasonal mortality trend was noted, with a significant increase related to air temperature greater than 20 degrees C and with a significant pre-spawning glycogen catabolism. Based on soft tissue flesh growth results from both types of culture, several empirical models were developed to assess overall yield from a spatial point of view. A N-NW positive trend was noted for the soft tissue flesh, suggesting a decrease in food availability towards the southern part of the bay. Yields (total weight) ranged from 85 to 2% for off-bottom cultures with 25 and 50% emersion times, respectively. For on-bottom culture, several sites have shown a negative yield down to -10% in the southern oyster bank sites. The highest yields were noted in areas located on the E-NE part of the Ronce oyster bank.