Développement d’un modèle de production ostréicole au sein d’une approche systémique pour la gestion intégrée de l’étang de Thau

Integrated Coastal Zone Management coordinates the development of systems modelling tools based on regional economic activity. A regional systems model created for the Thau lagoon (Languedoc Roussillon, France) includes a modelling tool for oyster production of Crassostrea gigas. Shellfish growth, estimates of stock and harvested production are simulated from a historical series of environmental forcing. One scenario shows the coherence of model output over the period 2000-2009 compared to baseline, although modifications are expected to refine the estimates (high death rate during dystrophic episodes, taken into account a new food forcing by flora and fauna selection). There is another scenario simulating the commercial ban of products from Thau Lagoon in September 2006 which revealed the weak impact generated on oyster production (range 6% of the marketable crop of 360 tonnes for a lag in sales of 11 days) although it’s possible that an economic impact exist at the enterprise level. The study of high death rate scenarios indicates losses of annual harvest of up to -79% between 2007 and 2009; the doubling of annual seeding in 2008 and 2009 would limit losses to 18% compared to a situation without high death rate. This kind of scenario is still approached with caution because of viral origin of high death rate and their probable density dependence. This exercise reveals now the contribution of such a model of oyster production both in the scenario analysis and on the improving knowledge of intrinsic model processes.