No deal and everyone suffers.
We're pursuing a theory at the expense of reality.
The theory is that we would expand the UK deep sea fishing fleet if we keep EU boats out of our waters. The fleet has been declining for centuries, not just the years in the EU. We can't expand it without foreign boats and foreign crews (because we already need foreign crews to make up for the lack of Brits willing to do it).
The reality is that our export trade (shellfish particularly) - with real current jobs at stake - would lose competitiveness if tariffs are applied, on top of the cost of customs red tape and the possibility of fatal delays at ports (i.e. the shellfish die en route), on top of low demand because Brits, and others, aren't going on holiday in the EU where they eat British shellfish (and half the continent isn't eating out at all).
Without a deal, EU fishermen go out of business, UK fishermen go out of business, there is less fish caught and sold, and it's obvious what this has to do the price of fish. We all pay more.