How the implementation of the European Commission's landing obligation (LO) would affect French vessels of the mixed demersal fishery in the Eastern English Channel was hardly foreseen because of the diversity of vessel characteristics and strategies in the area. Assessing whether the vessels would be able to mitigate the bio-economic impacts of LO and avoid choke situations through exemptions, by changing their fishing patterns or by avoiding areas, required fine scale spatio-temporal modelling of fish and fleet dynamics and of resulting technical interactions. We conducted a bio-economic impact assessment for seven scenarios of mitigation focussing on the differences across fleets and the impact of fleet spatial behavioural flexibility. We found that netters rapidly benefited from the LO as opposed to trawlers and that exemptions helped mitigate the economic loss with limited biomass loss. The avoidance strategies proved to be efficient in reducing unwanted catch of whiting and enabled unexpected protection of juvenile sole. Sensitivity analysis on the drivers of fishing behaviour indicated that the ability and efficiency of adapting fishing patterns depended on main gear and vessel size. Results evidenced the difficult trade-offs LO implies among stocks, fish stages, fleets, and even sub-regions, beyond the usual biological vs. economic contrasts.