Etude des causes potentielles des mortalités dans les élevages de crevettes pénéides nord médocains en 2001

For fifteen years, northern Medoc hosts sites of Penaeus japonicus. The six farms, with a total area of 180 ha (95 ha water) are supplied with water by canals connected to the Gironde estuary. Their normal total production is 11 tons per year, for an annual national output of 25 tonnes. In 2001, the survival rate of postlarvae were particularly low (22% average) compared to previous years, causing a decrease in production on all farms. A total of 4 tons of penaeid were harvested by farmers, about one third of normal production. To explain this sudden drop in production, farmers have questioned the possibility of pollution of the water feeding their marshes, suspecting especially the recent use of certain insecticides related to forestry and viticulture. A study was conducted in three of these marshes during the 2002 production season, mainly focused on investigating this hypothesis. However, the fact that other factors may explain the drop in output recorded in 2001, this study also involved the identification and compile some data acquired in 2001 to evaluate their possible impact on shrimp populations.