Site selection for stock replenishment using a hydrodynamic model: Example of the Pacific oyster Crassostrea gigas culture in the Pertuis Charentais (France)

No abstracts are to be cited without prior reference to the author.

The critical issue for oyster farmers in the Pertuis Charentais region of France is to obtain a sufficient spat supply on a yearly basis in areas dedicated to spat collecting to sustain oyster production. To address this practical question we searched for the main hydrodynamic factors driving spatfall abundance using a hydrodynamic model. Five hydrodynamic-related factors were included in the simulation: spawning time, pelagic larval durations, wind, broodstock location, and spat collecting location. The main result is that ”broodstock location” is the most important factor that impacts larval abundance above spat collection areas at the end of larval life. Northern beds supply spat areas located in the southern areas. This implies that the most important spatfall area in the mouth of the Charente River may be sustained by wild oysters, for which stocks are unknown. The importance of broodstock location implies an improved coordination between policy of eradication of wild oyster beds, aiming to increase productivity, and the policy of replenishment to improve the spatfall level. Moreover, it should be of concern when considering the development of farming of triploid oysters, which do not contribute to reproductive effort. Based upon those results, wild oyster stock assessment is a necessary step for determining where the replenishment should be carried out. The large variability of the contribution of oyster beds, however, seems to indicate that replenishment in well-chosen areas may be successful in improving spat supply.