Adapting a dynamic system model using life traits and local fishery knowledge — Application to a population of exploited marine bivalves (Ruditapes philippinarum) in a mesotidal coastal lagoon

Effective planning and management strategies of the Manila clam (Ruditapes philippinarum) stock in Arcachon Bay rely on a co-management approach, involving scientific advice and the fishing industry. In order to strengthen this management process, a specific compartmental single-species model has been developed to assess different management strategies. Based upon a size structure of the population and built from the dynamic systems paradigm, the modelling involves selected environmental and fishery-related parameters for their impact on the population dynamics. Integration of newly available life traits data regarding the local population and better knowledge of the fishing activity and its control parameters have enabled a revision of the existing version including model parameters and integration of new formulations. Effect of food availability and total suspended matter on the production of newly settled juveniles, natural mortality, growth rates, and price, accounted for the bulk of the undertaken improvements. Model performance was evaluated by comparing simulation outputs to observed data from stock assessments (2003, 2006, 2008, 2010, 2012, 2014 and 2018). In addition, a sensitivity analysis regarding uncertainty on parameters related to biological and environmental aspects was carried out to provide information about parameters that influence the outputs of the model the most. In particular, this highlighted that a deeper understanding of the processes related to the reproduction phase and its control parameters on biomass should be pursued. The improvements enable the calibration of the model with parameters that are as close as possible to the specificities of the stock considered. This adaptation permits use of the model to test various management strategies on the stock evolution and also to evaluate potential effects of environmental or market fluctuations. It encompasses ecological and socio-economic valuations of the measures of impact. As long as those objectives are shared by the different entities involved at the regional scale, communication and management decisions should be facilitated