Flatfish survivors have tales to tell: Cold seawater and reduced deployment duration contribute to the survival of European plaice (Pleuronectes platessa) discarded by Belgian beam trawlers

•Survival of undersized plaice was quantified on-board and post-release of Belgian beam trawlers.•On-board survival was as low as 20 % among vessels with >221 kW engine capacity.•On average 23 % (0–100 % CI) of plaice survived after 9 days.•Deployment duration, water temperature and vitality were negatively associated with survival.•Efforts to improve survival need to focus on capture rather than post-release stressors.