Testing policy before the fleet feels it: From a research tool to a policy instrument

All of the work described below (overview table below) starts from the same place: a skipper deciding where to go fishing next. Not a fleet average, not a grid cell with a fishing intensity in it, but a specific vessel with its own engine, fishing gear, home port, and account to settle at the end of the month. That is what “individual-based” in DISPLACE actually means.

Each fisheries-science model answers a different question, and each has earned its place. Stock assessment models estimate how many fish there are and how hard they are fished, which is the backbone of ICES advice; but because they represent fishing pressure as one number per stock, a closure and a quota cut can look the same to them. Aggregate bio-economic models capture the economics of fleet segments and suit questions where individual behaviour averages out. Static pressure maps show where fishing happens today and are invaluable for that, though by construction they describe a fleet at rest. The questions that motivated this body of work sit between those: which vessels lose their grounds when a rule changes, how far they travel to replace them, what the fuel costs, and where the removed pressure lands instead.

DISPLACE was built for that in-between territory. Conditioned on VMS and logbook data, it simulates each vessel choosing among its known grounds under whatever constraint the scenario imposes, while fish stocks respond spatially to what the fleet does, and the fleet responds back.

The 2020 Baltic study (Bastardie et al., 2020) gave one of the first warnings: closing an area does not mean the seafloor would recover, because vessels shift to the next best grounds and the added pressure there can offset what the closure gained. Seeing that requires simulating behaviour, not assuming it away. The 2025 SEAwise study (Bastardie et al., 2025) showed the complementary result: blanket trawling bans in all MPAs might cut fleet economics by 25-30%, while restricting trawling only where benthic communities are made up of long-lived animals would cost the fleet little. Telling those two options apart depends on knowing each vessel’s real alternatives. The 2022 fuel paper (Bastardie et al., 2022) stated that rebuilt stocks would cut fuel use more than new gear would do, because fuel is spent trip by trip and better catch shortens trips. CAFF and MarineGuardian projects now extend that accounting to fleet renewal and decarbonisation scenarios, helping the sector to commit to a transition path.

Meanwhile, the model keeps travelling 🙂 the Ionian Sea (Maina et al., 2021), western Baltic cod (Rufener et al., 2023), deep-sea VME closures weighed in STECF advice, and offshore wind leases off California. The “new rule” there is not even a fishing measure but someone else claiming the sea.

Looked at together, the arc of these papers is about finding the right unit of analysis for the question at hand. Stock models count fish, economic models track fleets, pressure maps map square kilometres. Some questions need all three scales at once: a skipper’s reaction, the next ground chosen, the fuel burned, the fish removed, the seafloor swept. As policy keeps redrawing the map of European seas, decisions are made at that scale, vessel by vessel.

DISPLACE (2020–2026)

● = core; ○ = secondary.

Francois Bastardie

Francois Bastardie is a DTU-Aqua Senior Scientist and method developer in the Section of Ecosystem-based Marine Management with a Ph.D. in Biological Science. He has been involved in several national and EU Funded projects developing expertise in spatial fisheries and fisheries databases. He has a strong background in modeling fishing and the bio-economic dynamics including developing agent-based models for combining marine ecosystems and natural resource extraction models, fisheries economics in a mixed fisheries perspective. He has an experience of 10 years leading to more than 35 peer-reviewed publications by conducting scientific-based fisheries management evaluation with scenario-testing evaluation and simulations, including fleet dynamics and consequences on the economy of fisheries, population dynamics and fish stock assessment. He was in charge of the evaluation of some of the EU long-term fisheries management plans with consequent participation to ICES and STECF working groups, including giving advise from regional to international policy makers.

Author: Francois Bastardie

Francois Bastardie is a DTU-Aqua Senior Scientist and method developer in the Section of Ecosystem-based Marine Management with a Ph.D. in Biological Science. He has been involved in several national and EU Funded projects developing expertise in spatial fisheries and fisheries databases. He has a strong background in modeling fishing and the bio-economic dynamics including developing agent-based models for combining marine ecosystems and natural resource extraction models, fisheries economics in a mixed fisheries perspective. He has an experience of 10 years leading to more than 35 peer-reviewed publications by conducting scientific-based fisheries management evaluation with scenario-testing evaluation and simulations, including fleet dynamics and consequences on the economy of fisheries, population dynamics and fish stock assessment. He was in charge of the evaluation of some of the EU long-term fisheries management plans with consequent participation to ICES and STECF working groups, including giving advise from regional to international policy makers. View all posts by Francois Bastardie