The more we block other nations from raping our fish supplies, the more valuable the fish will become.
As the rest of the world runs out of fish, NZ will be able to sell 'some' of its fish resource to the highest bidder at much better rates than they currently get.
The problem is protecting it from those who would just steal it. Our Navy, (consisting of a couple of row boats) won't be able to fend off all the thieves from the northern hemisphere.