ReMoNor : Mise en place et premier bilan du Reseau Mollusque de NORmandie (1998-1999)

Since 1998, a growth and quality monitoring study of reared molluscs has been developped as part of a close collaboration between the Shellfish Research Laboratory of Normandy (IFREMER Port-en-Bessin, Calvados) and the SMEL (Syndicat Mixte d'Expansion du Littoral) Experimental Centre (Blainville, Manche). REMONOR (REseau MOllusque de NORmandie) is based on the experience gained through the national monitoring network REMORA, which protocol has been entirely applied. Adults and spat of Pacific oysters Crassostrea gigas were placed in 13 stations all along the oysters rearing areas of Normandy. These oysters had the same origin and history (i.e. age and weight) until they were dispatched on the 13 stations. 4 essential criteria were used to monitor rearing performance : seasonal and annual mortality, growth (daily weight , seasonal growth rate and weight growth rate), quality (length, width and height coefficients, quality index [Afnor], condition index [Lawrence & Scott] and Polydora index) and production level (survival x weight). This report presents the results from the two first years of the REMONOR program. Monitoring of seasonal mortality allows characterisation of anomalies encountered in the rearing of livestock during the year. 1998 and 1999 did not show any major accidents similar to those observed the past few years by REMORA monitoring program. Annual average mortality spanned from 5 to 15%. Seasonal growth monitoring showed specific answers of each age class to seasonal variations. 1999 autumnal growth was very high. However, yearly growth remained normal compared to previous annual results. In spite of a production level lower than 2 (reference value) in some areas, global regional yields remained equal to those previously observed previous years. This is due to both low mortality and growth performance still maintained. Globally these first 2 years of monitoring showed a steady situation, similar to previous years. Growth during autumn was high, and production level was good. Quality index was high but infestation by Polydora needs to be watched over.