One of the final outstanding issues in the post-Brexit trade talks between the United Kingdom (UK) and the European Union (EU) is fishing, which has always been an emotional issue in the UK's relationship with the EU. Fishing is a tiny part of the economy on both sides of the English Channel, however, it carries big political weight.
Brexit supporters see it as a symbol of sovereignty that will now be regained. UK said any new agreement on fisheries must be based on the understanding that "British fishing grounds are first and foremost for British boats," reports the BBC.
However, the EU wants access for its boats and said its trying to reach a "fair deal" on fisheries is a pre-condition for a free trade agreement - with no tariffs or taxes on goods crossing borders.
UK formally left the EU on 31 January, but is still bound by the EU's rules, including its Common Fisheries Policy (CFP) until the end of this year. This would mean the fishing fleets of every country involved have full access to each other's waters, apart from the first 12 nautical miles (14 miles; 22km) out from the coast.
EU ministers gather for marathon talks every December to haggle over the volume of fish that can be caught from each species. National quotas are then divided up using historical data going back to the 1970s, a time that the UK fishing industry said it got a bad deal. Therefore, UK government wants to increase the British quota share significantly.
The argument is further complicated by the fact that parts of the British quota have been sold off by British skippers to boats based elsewhere in the EU. In England, for example, more than half the quota is in foreign hands. More than 60% of the tonnage landed from English waters is caught by foreign boats.
Outside the EU, as an "independent coastal state", the UK will control what is known as an exclusive economic zone (EEZ) that stretches up to 200 nautical miles into the North Atlantic. Inside the EU, the EEZs of all member countries are managed jointly as a common resource.
UK government wants to hold annual talks on access to UK and EU waters, and on quotas - using a system that works out shares based on the percentage of each species of fish in each EEZ - this is known as "zonal attachment". Other independent coastal states such as Norway also practice this. The fishing communities in the UK, which were strong supporters of the campaign to leave the EU, are insisting on this basic change.
But as the UK waters are important and bountiful, the EU is under huge pressure from its fishing communities to maintain as much of the status quo as possible. It wants the UK to grant significant access, with only gradual change envisaged, in order to "avoid economic dislocation for EU fishermen that have traditionally fished in UK waters".
The EU also wants to divide up the amounts that each country's boats are allowed to catch in a way that will not be renegotiated every year, and which cannot be changed unless both the UK and the EU agree. EU's chief negotiator Michel Barnier has said in the past that annual negotiations with the UK would be technically impossible because so many different types of fish would be involved.
Catching fish is not the only catch
It is not just about where fish can be caught - but also about where fish can be sold. This is particularly important, because most of the fish landed by UK fishermen is exported, while most of the fish eaten in the UK is imported.
Of all those exported fish, roughly three quarters are sold within the EU. Some parts of the industry - such as shellfish - are totally dependent on such exports and would collapse if they were suddenly faced with tariffs or taxes on their products. It is one of the reasons why the UK argues access to markets should be nothing to do with access to fishing waters.
EU is making the link explicit, insisting that without a deal on fish, there will be no special access to the EU single market. Some ministers have even said that if the UK blocks access to fishing waters they can't guarantee full access to EU energy supplies.
Fishing is only a tiny fraction of the overall economy both in the UK (less than 0.1%) and in the EU - where some landlocked countries have no fishing fleets at all. According to UK's Office for National Statistics, fishing was worth £784m to the UK economy in 2018. By comparison, the financial services industry was worth £132bn.
Fishing is a major source of employment in many coastal communities - responsible for thousands of jobs. The industry still has political power, and both the UK and the EU are under pressure not to give ground. A final compromise is likely to involve the UK guaranteeing a certain level of access to EU boats, which is lower than they have now.
Any proposed deal on fishing needs the agreement of all EU countries - it can't just be signed off by the European Commission.