KILKEEL, Northern Ireland (AP) — When it comes to U.K.-European Union relations, there’s nothing like slapping a fish around. After all, both sides have been contesting who rules their waves practicallysince the United Kingdom became a member in 1973.

So it’s not so surprising that once the U.K. officially leaves the EU on Friday night, one of th e first things the two sides will wrestle over during negotiations on their post-divorce relationship is the comparatively tiny fisheries industry.

“Perhaps in many ways, fisheries is the acid test of Brexit,” said British politician and leading Brexiteer Nigel Farage.

Industry and financial services are much more important in sheer economic terms. But somehow fish and chips in Britain and sole meuniere on the continent stir much stronger emotions.

“For example, our car industry and chemicals industry alone are worth 20 times the value of the fishing industry,” said Chris Davies, an English Liberal Democrat member of the European Parliament who is head of the EU’s fisheries committee until he leaves on Friday.

“It is much more important, of course, to the economy in Britain as a whole that we get access for those products,” Davies said.

But that doesn’t ring right in Kilkeel, Northern Ireland, and other U.K. ports, where resentment runs deep against EU fishing policies that allow vessels from other nations in the bloc to catch stocks in rich British waters.

“This fleet has been stymied now for, what, 30, 30-plus years, in terms of fish being taken off us and given to other member states. It has been a struggle,” said Alan McCulla, CEO of the local ANIFPO fishing cooperative.

“Fishermen here have lost thousands of tonnes of fishing opportunities valued at millions of pounds,” McCulla said.

Brexiteers have thrived for years on similar words of perceived wrongdoing by faceless bureaucrats encroaching on age-old British sovereignty. And no one has done that more effectively than Farage, who has been driving the U.K. towards the EU’s exit door for decades, mostly from inside the European Parliament itself — where he served as a British lawmaker for over two decades.

Farage knows how the briny whiff of the sea tugs at the nation’s heartstrings.

“The greatness of Britain has always been what we’ve done on the seas, whether it’s through the Royal Navy or through our merchant fleets,” Farage said in an interview with The Associated Press. “So fisheries is actually — symbolically — very, very important.”

Farage led a flotilla of fishing boats up the River Thames to Britain’s Parliament in last-ditch campaigning before the Brexit referendum on June 23, 2016. It turned out that every bit helped, as British voters stunningly decided to leave the bloc by a narrow 52%-48 % margin.

Fish in waters off Britain were still abundant in the 1970s and fishing towns still thrived.

But for just about the duration of Britain’s EU membership, fish stocks ranging from North Sea cod to English Channel sole have been in decline. And for British fishermen it was easy to point fingers at foreign fishing vessels and EU headquarters in Brussels. Every coastal EU nation wanted to catch as many fish as possible, despite dwindling stocks and scientific warnings about overfishing.

First, the EU forced boats to stay in port and restricted quotas, limiting access to fish. And when British fishermen then saw EU boats in their shared waters, anger came naturally.

The broad promise of Brexit always was to regain control, which many in the industry will feel when a 200-nautical mile zone is set for the U.K., instead of the current 12 miles.

“The U.K. should determine what level of access from EU boats is allowed in. It shouldn’t be a free-for-all just because they’ve been there for years and years. The rules have changed, and we’re taking back control of our own waters,” said fisherman Brian Chambers.

Chambers, who owns the “Boy Paul” with his brother and mainly fishes off the coast of Ireland and the Isle of Man for crab and scallops, was among those voting to leave the EU.

Farage says Brexit could make sure that boom years lie ahead for Britain’s 8,000 fishermen who net just under 1 billion euros ($1.1 billion) worth of annual catches.

“If we get fisheries right, we will bring tens of thousands of jobs back to our coastal communities,” he said.

However, the EU has already made it clear negotiations won’t be that simple. Chief negotiator Michel Barnier’s office has already informed diplomats from the 27 member states that “reciprocal access to fishing waters and resources should be maintained.” That means pretty much looking for the status quo that U.K. fishermen hate so much.

And the EU can also play the history card.

“European vessels have been fishing in those waters forever. The Vikings would have dragged a net behind their longboats when they came over 1,000 years ago,” said Davies. “So, not surprisingly, the Dutch and the French and others are saying ‘we want this to continue, historically, it’s our right.’”

Furthermore, while Britons may have their fish-rich waters, the EU has an even richer consumer market.

“British fishermen are going to have to accept that so long as they are selling 70% of all the fish they catch into the European continental market, their bargaining power is not that great,” Davies said.

Again, fishermen can already feel the squeeze. Even if they are revered and romanticized for being some of the last true hunters in Europe, many have long been squeezed out economically. As fish needed to be protected, they felt the politicians didn’t protect them. The promise of Brexit gave them a new hope, but now the realities of hard-nosed negotiations set in.

The fear is that their desire to get better ownership of their fishing grounds might just become another pawns in the trade talks between both sides.

McCulla of the ANIFPO cooperative is trying to look at the bright side.

“I’ve no doubt that Europeans will still be able to fish in U.K. waters in the future,” he said. “But the important difference is that they will have to have that access under the terms of U.K. PLC, not under the terms of Brussels. And in the future, Britannia will rule Britannia’s waves.”

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Follow AP’s full coverage of Brexit and British politics at: https://www.apnews.com/Brexit.

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Raf Casert reported from Brussels.