For the ecosystem approach to fisheries management, understanding population dynamics and ecosystem resilience in response to the landing obligation acted by the reform of the European Common Fishery Policy (CFP) is currently an important avenue of research. This study attempts to assess the impact of the new CFP on marine food webs. Total carbon and nitrogen loss induced by a discard ban were estimated for the ecosystem of the Bay of Biscay based on French At-Sea Observer data and carbon and nitrogen content of discarded fish. Changes in predator diets were estimated by comparing two Bayesian mixing models, one mimicking the current situation and the second the application of the new CFP (removing the discarded species that would be landed from the model). Results illustrate a substantial shift in predation effort toward remaining available prey. The impact of changes in diet on individual and population health and on ecosystem functioning are important issues that remain to be assessed. A sister study could be carry out in another ecoregion, at a finer spatial scale in order to compare impacts and ecosystem responses. European monitoring programs such as DC-MAP and the Marine Strategy Framework Directive (MSFD) would help us to gain an understanding of how the food web would reorganize itself.