You are confounding several things. It is NEVER cheaper to import than to fish, because importing costs money and fishing does not.
What you mean is that the opportunity cost of fishing is higher than its market value, meaning that there is another job that you can do for 8 hours that would make you more money than the fish that you could have caught in 8 hours would be worth. For that to be true, you need that job to exist that you can do, which is not always true in high unemployment situations.
And when that IS true, then it is a good thing, because that means that the economy as a whole is working more efficiently - you are not spending your time doing useless things, you do something more productive instead.
