[Sephiroth]

https://britishseafishing.co.uk/brexit-and-britains-fisheries/

This article provides some perspective on what the fishing argument is all about (my bold highlight).

The way quotas are set centrally by the EU is also seen as being hugely unfair on British fishermen, as they can often end up getting only a tiny proportion of the catch within their own waters, as the following statistics show:

40% of Denmark’s entire fishing take comes from Britain’s territorial waters.
In the Celtic Sea, France gets nearly three times the British allocation of Dover sole, roughly four times more cod and five times more haddock. France has 84% of the quota for cod in the English Channel, while Britain has only 9%.

A single Dutch trawler the Cornelis Vrolijk, had the right to catch 23% of England’s entire fishing quota. In comparison the entire small inshore fishing fleet for the whole England is given 4% of the quota.

European fishermen take 173 times more herring, 45 times more whiting, 16 times more mackerel and 14 times more haddock and cod out of UK waters than British fishermen do.