Well,there's a fucking surprise.

https://fullfact.org/europe/eu-pinching-our-fish/

The UK’s share of the overall EU fishing catch grew between 2004 and 2014. In 2004 the UK had the fourth largest catch of any EU country at 652,000 tonnes, by 2014 this had grown to 752,000 tonnes and the second largest catch of any country in the EU.
And another:

Total Allowable Catches are intended to ensure that fishing is sustainable within each fishing zone and that the areas are not overfished. There are doubts within the industry as to whether or not the EU’s fishing policy has actually achieved this. But, some species, such as North Sea cod, seem to be recovering and an assessment is underway to determine whether or not it is now sustainable.
Shock/horror

If we left the EU it wouldn’t necessarily mean that the situation would improve. The House of Commons Library has said that “many of the underlying issues that affect fisheries management would remain unchanged.”