Marine zones of controlled fishing in the Pacific Ocean could greatly improve numbers of heavily overfished tuna and improve local economies, a study says. Scientists at the University of Hawaii at Manoa, working with colleagues from French and South Pacific institutions, said a network of marine zones where different fishing activities are allowed in different areas could be a more effective conservation measure than simply closing relatively small areas to some types of fishing. \"We found that simply closing areas off to fishing doesn\'t work, because the boats just move their operations to neighboring zones and fish even harder,\" said John Silbert of the University of Hawaii Joint Institute of Marine and Atmospheric Research. \"It\'s going to need a combination of approaches.\" Half the current bigeye tuna catch is by longline, which targets high-value tuna sold as fresh fish, while the other half is caught in purse-seine nets as incidental bycatch when aiming to catch skipjack tuna. Juvenile bigeye tuna caught in these nets are sold to the canning industry. The most effective measures to protect tuna numbers would be marine zones that restrict longline fishing in tuna-spawning areas, the researchers said, and where the use of fish-aggregating devices such as moored or drifting buoys which attract fish in purse-seine areas is regulated. The best conservation measures, Silbert said, are those \"which protect fish throughout their lifetime.\"