Fishing fleets in the western Pacific ocean could double their tuna catch by following the same warm ocean waters that are responsible for the El Ni�o weather system.

About half the world's supply of tuna - one and a half million tonnes - comes from the western and central Pacific ocean.

By monitoring the movement of the ocean's surface waters, fisheries scientists discovered that tuna concentrate where a warm region of water in the west meets a cooler water mass to the east.

Over a seven year cycle, this tuna-rich area shifts position by almost two thousand kilometres. During an El Ni�o year, the zone is at its most easterly point which means it is now possible to predict with accuracy where the tuna can be found in two months.

As satellite survellience and computer models of the ocean circulation improve, six-month forecasts should be possible.

The information could help fishing fleets enormously in planning where and when to fish for a maximum catch.

According to the scientists, western Pacific tuna stocks are at very healthy levels and - although they say monitoring fish populations and catches will continue to be vital work - they are confident that heavier fishing would be sustainable.