Fisheries management imposes constraints on fisheries. Yet, fishers are able to adapt and change their behaviour in relation to imposed constraints. These choices include decisions on when and where to fish, which species to target or throw back into the sea (discarding). The effect of behavioural adaptations on the success of fisheries management is often overlooked by policymakers. Models developed in this thesis provide a strong basis to explore possible unexpected effects of management measures, such as the discard ban, resulting from the adaptive behaviour of fishers. We applied these models to study the behavioural adaptations of the Dutch flatfish fisheries and the French mixed demersal fisheries in the Channel. Outcomes draw attention to the importance of making fleet dynamics an integral part of fisheries management. We also address the need to develop innovative analytical methodologies which deliver robust insights into complex socioeconomic and ecosystem issues to improve decision making.