Mackerels are adaptable animals: they live in very different seas, from the Mediterranean coasts to the Faroe Islands. For the last ten years or so they have also frequented the waters of Greenland, the Svalbard Islands and Iceland, which now wants its share in the fishing quota system established between the northern European countries, to the detriment of the countries that have always shared them out, thus creating international disputes. Since the end of the 19th century, the countries bordering the North Sea (and the Atlantic Ocean) have been trying to agree on how much and what fish each of them can catch. In 1902, the ‘International Council for the Exploration of the Sea’ (ICES) was founded in Copenhagen, a scientific organisation with 20 member countries (membership is voluntary and decisions are not binding) which, for each commercially fished species, estimates each year the quantities that can be caught without leading to extinction. Since mackerel have changed their migratory routes, the northern European countries that fish them cannot find a compromise, even on the basis of ICES estimates: the situation can become problematic, even leading to the extinction of a species. For example, fifteen years ago the population of blue whiting fell from 2 million tonnes to less than 40 thousand within five years. As for mackerel, there has been an abundance in recent years, but things may change in the future: in 2018, the ICES advised a maximum annual catch of 550 thousand tonnes, but the EU, Norway and the Faroe Islands agreed to go up to 800 thousand tonnes, without setting a shared limit with Iceland, Russia and Greenland. In the end, almost 1 million tonnes of mackerel were caught, about twice as much as ICES scientists suggested to safeguard the species. Atlantic mackerel spend the warmer months of the year close to the coasts of northern Europe, but in the autumn they migrate to more southerly waters, where they spend the winter: they spawn in the spring in waters around Ireland and Great Britain, then move north towards Norway, the Faroe Islands and Iceland, before returning south. They move in very large shoals and grow over the course of the year: when in Norwegian waters they are bigger and fatter. In the past, the Norwegians and the Faroese did not appreciate mackerel very much: in northern Norway, for example, there was a superstition that the firmness of their flesh was due to the fact that they ate the bodies of sailors who died at sea. The real problem was that until the 1960s, before fishing boats were equipped with refrigeration systems, mackerel were only eaten after they had been smoked, or in the pickled version, because they no longer tasted good when they arrived in ports. Alternatively, they were used as bait for cod. However, the introduction of refrigerators and Japan’s interest in European mackerel, which began in the 1980s, drove up prices: today about 40% of the revenues of many Norwegian fishing companies come from mackerel. In Iceland, on the other hand, mackerel were not eaten because they simply weren’t there: things changed when they began to appear more and more often in the trawl nets used for herring. In 2006, Páll Guðmundsson, director of the fishing company ‘Huginn EHF’, asked the ‘Icelandic Ministry of Fisheries’ and the ‘Sea and Freshwater Research Institute’, a governmental scientific body concerned with Iceland’s water resources, to verify that the amount of mackerel in the ocean around the island was sufficient to justify fishing. The following year he was able to fund the mackerel research himself and Icelandic fishermen caught 32 thousand tonnes of mackerel, compared to 4200 tonnes the year before. By 2008, the total had reached 110000 tonnes and the Icelandic government decided that it would try to obtain a quota for mackerel catches in the international system, which at the time included the EU, Norway, Russia and the Faroe Islands. Initially, these countries refused to grant Iceland the right to fish for mackerel, but by 2010 it was clear to everyone that mackerel were present in Icelandic waters: the problem was that Iceland had always demanded a larger share of the catch than the other countries were willing to grant it. The Faroese government also began to make greater demands and in 2011 the archipelago decided to opt out of the international agreement on mackerel fishing, and then to fish for more herring. This led the EU to impose an embargo on Faroese fish, until the 2014 agreement between the EU, Norway and the Faroe Islands, with the latter’s share of the mackerel catch increasing from 5 to 13% of the total allowed internationally. Since then, however, no agreement has ever been reached with the other countries that fish mackerel, namely Iceland, Greenland and Russia, which, although it has no mackerel in its waters, has historically fished them in the north-east Atlantic. The fact that a country’s economic sector depends on fishing a species for historical reasons has always been a valid argument for granting access to quotas. The 2014 agreement between the Faroe Islands, the EU and Norway (renewed in 2018 and 2019, and expiring with the end of 2020) left Russia, Iceland and Greenland with 15.6% of the total mackerel that could be fished, but in recent years Icelandic fishermen alone have fished around 16.5% of the total set by ICES. Brexit has complicated things: with the exit from the EU, the UK has become a new independent player in negotiations on fishing quotas. In the meantime, the UK and the EU have agreed that until 2026 marine resources will still be partly shared, without clarifying the case of mackerel: as things stand, there is no international agreement in place, which is why now neither Norwegian nor Faroese fishermen can fish in British waters, where they normally fish part of their quotas. It is difficult to predict if and how the numbers of mackerel will change in the coming years, because there are many factors at play and scientists disagree on why they are moving further north: some think it has something to do with the rise in the average temperature of ocean waters, but according to other scientists mackerel have moved to Iceland because they have increased in numbers and needed to expand into new hunting areas. These differences in interpretation of the available data are among the reasons why the ICES annual estimates have margins of error and are often contested by countries that would like to fish more: the ICES estimates are not so much a tool to ensure the long-term sustainability of fisheries, but rather a way to give governments numbers to negotiate from. Ideas about how many fish there are in the sea are still unclear.