Mathilde Mahé will present her thesis on Wednesday 23 February 2022 at 9:00 am

on the following topic:

"Sustainable management of a fishery resource using a model: example of Ruditapes philippinarum (Adams and Reeve, 1850) in the Etang de Berre"

Thesis director: Jean-Christophe Poggiale, professor AMU

SUMMARY : The objective of this thesis is the sustainable management of a fishery resource, with the example of the Manila clam Ruditapes philippinarum (Adams et Reeve, 1850) in the Berre lagoon (near Marseille - France). In order to better adapt a fishery management model in the Etang de Berre, it is necessary to improve the knowledge of this species in this environment based on in situ experiments. The size is 20 - 23 mm. Clams reproduce between March - April and September - October when water temperatures are above 11°C. The VBGF parameters are and . In the Etang de Berre, predation is considered negligible. Natural mortality is therefore related to senescence and diseases, which have a fairly low prevalence, it varies between 0.64 and 2.85 depending on the size of the individuals. In 2019, a campaign on the whole pond of Berre between 0 and 5 m showed that the abundance was 552.07 million individuals for a biomass of 2,903.62 tons; with a strong disparity in the distribution: two areas represented 69% of the total abundance and 80% of the total biomass. These areas have been monitored regularly and show a decrease in abundance of 10% probably due to poaching. Foot fishing was addressed by counts and was estimated at 62 tons of clams for the summer of 2018. On an annual scale, professional fishing pressure is 142 tons. All of these in situ data are integrated into a management model combining an individual DEB model feeding a population model in three size categories (juvenile, adult between 20 and 30 mm and adult with mesh size). The outputs of the model are used to compare fishing scenarios during COPIL and to assist in decision making. The methodology developed in this thesis can be transposed to other species and environment pairs. The originality of this thesis is to have carried out all these works in parallel. Each study was fed by the others and vice versa.

KEYWORDS : Ruditapes philippinarum, étang de Berre, life cycle, model, fisheries management.