The majority do understand the economic impact but have less concern for it than the return of British sovereignty. Trade with the continent will resume as the UK is a prime partner. One of the largest issues was that Britain, Wales, and Ireland want their fishing rights to stay within the power of the UK and not the EU.
Yes, and fishing and fish processing contributes almost 1/8 of 1% of UK GDP.
But of course, after financial services and manufacturing de-camp for greener pastures, fishing will be a larger % of a much smaller economy, so will be relatively more important.