The breakthrough came at around 3 a.m. on 30 May in Brussels, after a marathon negotiating session: the European Union (EU) finally agreed to end overfishing in its troubled waters.

Fisheries scientists say that the deal, which is expected to be approved before the end of the year, could allow fish stocks to recover to their previous bountiful levels, after being driven down by years of overfishing. But short-term restrictions are likely to bring unemployment to some fishermen.

“There is bound to be some short-term pain, says Michel Kaiser, who studies fisheries at Bangor University, UK. “This reform has come about because there was a groundswell of realization that what we had before couldn’t go on.

The deal places scientific advice at center-stage in determining catch limits, as the EU commits to fishing at healthy levels by 2015 “where possible and by 2020 otherwise. New rules will also be phased in to reduce ecologically damaging ‘discards’ the practice of throwing fish caught in the pursuit of other species back into the sea, with the vast majority dying in the process.

For years, scientists have warned that more fish were being caught than was sustainable, owing to a flawed ‘Common Fisheries Policy’ (CFP), which governs commercial fishing in European waters. Government ministers set higher catch limits for cod, haddock and some other species than scientists considered wise (see ‘A waning haul’). The latest agreement, which has been several years in the making, is backed by the three arms of European government: the commission, parliament and council. Parliament had been pushing for a thorough reform of the CFP to put catches in line with what science says is sustainable, whereas the council made up of ministers from EU member states had been less amenable to radical change.

Environmentalists are generally pleased with the deal’s main thrust: a commitment to fishing at maximum sustainable yield (MSY), the largest catch of a particular species that can be taken indefinitely without harming the main population. Scientists have two measures for MSY, obtained using mathematical models created with data from catches by commercial and research vessels: the overall biomass of a species needed to maintain MSY (BMSY) and the annual amount of fish taken from that species that will still allow the species to reach BMSY (FMSY). Fishing at a higher level than FMSY means the fishing is unsustainable in the long term. Environmentalists prefer BMSY to FMSY as a target, because reaching the former would show that a stock has actually recovered, whereas fishing in line with the latter indicates that a stock is on the road to recovery.

2013 Scientific American, a Division of Nature America, Inc.