When fish are allowed to rest in one area, it helps increase fishing elsewhere.  Only 8% of the commercial catch comes from the area in question.  In other words, shutting down such a large swath won't reduce the total catch by very much, but it does give our fisheries a place to rest and breed, which will help the fisheries in the long run.  Westpac is in place to whine and try to control the ocean, but its stakeholders are fishermen and its goals are short-term profit.