The ban on discarding unwanted fish overboard when fishing, which was decided during the last 2013 EU Common Fisheries Policy reform, requires that everything retained in a commercial fishing gear is recorded and counted against fish quotas when some exist like in Northern European waters. It is, however, difficult to reduce catches of a single fish species when a variety of fish is generally caught together. This creates a risk for early closures of fisheries when the quota of one fish (the “choke species”) is exhausted before the others. To cope with this and avoid an unnecessary low rate of quota utilization, fishermen can try to lease extra quotas, or modify their catches, either by switching to more selective fishing gear types or through changes in when, where and how to fish, by trying to avoid areas where there is a fair amount of possible choke species, and displace the fishery as soon as a large catch of choke species is encountered. This ability to displace will depend on the skills and choices of the skipper but also on how the fish stocks distribute in space and time (patchily vs. evenly distributed). We are developing here a platform to test such interlinked effects in a clear and detailed manner by accounting for varying skipper’s decision-making, such as for example the one described in the adjacent decision tree.
