It's about Great Britain actually agreeing to abide by some of the agreements it signed up to as a result of Brexit.
Not specific to the Jersey dispute but relevant nonetheless;
April 23, 2021
At the heart of the dispute is whether the criteria agreed in the withdrawal agreement make it difficult for fishermen to qualify for licenses, or whether the British are dragging their feet in delivering licenses.
French fishermen acknowledge the British are right when it comes to the small print of the withdrawal agreement, but say they don’t respect the spirit of the deal.
“The global deal looked superb, but it was too good to be true,” says Olivier Leprêtre, president of the regional fisheries committee in the Hauts-de-France. “When we started sifting through the 1,200 pages of the agreement, we realized that there are lots of blocking criteria. Ultimately, we have been almost completely excluded from British waters."
Leprêtre says criteria on netting, fish species and fishing zone demarcation are particularly problematic.
According to the EU commission, there is no specific tool in the EU-U.K. post-Brexit agreement to tackle a blockage on fishing licenses, apart from the general dispute settlement mechanism.
www.politico.eu/article/french-fishermen-threaten-to-block-calais-port-over-brexit-dispute/
Jersey -
A French government threat to cut off Jersey's electricity over a post-Brexit fishing dispute was "clearly unacceptable and disproportionate", the UK government has said. ...
Jersey issued 41 licences for access to its waters on Friday when an interim agreement came to an end.
The Jersey government said the permits must "correspond to the previous activity a vessel has carried out in Jersey waters" under the terms of the TCA and its new system was "in line with the data submitted by the French and EU authorities".
A spokeswoman said it took French complaints over the terms of the licensing agreement "very seriously" and would respond, but said it had acted in "good faith" setting up the regime.
"The government remains committed to the sustainable management of Jersey waters for the benefit of this and future generations,"
Speaking to BBC Radio 4's Today programme, Ian Gorst, External Relations Minister for the Government of Jersey, argued there was no justification for such severe measures.
"It would seem disproportionate to cut off electricity for the sake of needing to provide extra details so that we can refine the licences."
On Tuesday, he explained there was "no time limit" for the French fishing industry or government to provide evidence of previous activity in Jersey waters and he wanted to "heal this relationship".
"If French fishermen or the authorities have further evidence they would like to submit, we will update the licences to reflect that evidence."
French authorities said "new technical measures" for fishing off the Channel Islands had not been communicated to the EU, rendering them "null and void"...
The UK's Department for Environment, Food and Rural Affairs said the self-governing Crown Dependency is "responsible for its own territorial waters".
www.bbc.co.uk/news/world-europe-jersey-56991804
Oh dear;
France’s reaction to post-Brexit fishing restrictions around the island of Jersey has been branded “pretty close to an act of war” by fishing community leaders in St Helier.
They say they have been told 100 boats are being lined up in France for a 6am blockade at the main Channel Island port on Thursday threatening food and energy supplies.
“It was inevitable that the French would kick off,” said head of the Jersey Fishermen’s Association, Don Thompson.
Brexit had given Jersey the authority to manage its own waters and for the first time and was exercising its legal right to apply conditions in line with sustainability goals.
But not everyone agrees in the local fishing sector.
The island’s leading oyster and mussel fisherman, Chris Le Masurier, is scathing and says the problem is not Brexit but the local government’s “incompetent bunch of idiots”.
www.theguardian.com/uk-news/2021/may/05/jersey-fishing-row-french-threats-pretty-close-to-act-of-war
It's difficult to say whose fault it is but clearly the French are acting disproportionately.