Penning fish in open waterways is also problematic. Fish farming is best done in indoor, onshore facilities. The fish rarely escape, and the wastewater can be treated before being released. Growing vegetarian species such as tilapia is ideal, since they don't have to be fed wild fish. The biologically richest stretches of ocean are more disrupted than the richest places on land.
Continents still have roadless wilderness areas where motorized vehicles have never gone.
But on the world's continental shelves it is hard to find places where boats dragging nets haven't etched tracks into sea-floor habitats. In Europe's North Sea and along New England's Georges Bank and Australia's Queensland coast, trawlers may scour the bottom four to eight times every year. And the U.S. National Marine Sanctuaries hardly deserve the name. New Zealand and the Philippines are among the countries that have established reserves in which fish are actually left alone. Marine life tends to recover in these areas, then disperse beyond them, providing cheap insurance against overfishing outside the reserves.