I think that discussing the issues of enforcement is something of a distraction at the moment - and probably this was started by a poster that just needs to run the UK down - by gloating over the number of boats, speed they travel and the area to be covered etc.
The key point would be that trawlers from EU countries would have to decide to knowingly break the law
Should they decide to do that then decisions and plans on enforcement can then be taken/made.
Hopefully, sometime in 2021 we will start to see all UK citizens looking to the good of the UK and this need for some to belittle the UK and hope for bad outcomes for the UK will recede