The project in 12 tropical nations, including Mexico and the Philippines, "has dramatically cut the unwanted catch of young fish, turtles and other 'by-catch' by as much as 30 to 70 percent," the UN Environment Programme said in a statement.

"We are seeing some promising preliminary results," said Monique Barbut, the head of the UN's Global Environment Facility which is funding a four-year-old project costing more than US$9 million.

"Over 60 percent of what is currently caught in the global shrimp fishery is discarded, making it among the most environmentally damaging in the world," she said.

Worldwide losses -- mostly because young fish are caught before they reach maturity -- are estimated at billions of dollars, adding to problems of overfishing.

New trawler nets include metal grilles that let shrimp through into the main bulb-shape net but stop bigger fish or turtles and force them out through an "exit hole" in the side.

Other types of nets have large holes on the sides near the front -- fish are smart enough to swim out against the pull of the trawler while shrimp lack the intelligence to spot the exit.

The United States is among countries banning wild shrimp imports from nations that do not use such environmentally friendly nets. The UN-funded measures also include training, high tech sensors and underwater monitors that help efficiency.

"There are important lessons to be learnt here for other fisheries and indeed across a wide range of environmental challenges from forestry to energy," said Achim Steiner, head of the UN Environment Programme.

The project comprised Indonesia, the Philippines, Cameroon, Nigeria, Bahrain, Iran, Colombia, Cuba, Costa Rica, Trinidad and Tobago, Venezuela and Mexico.

The global marine shrimp catch in 2004 totalled 3.47 million tonnes, or four percent of marine capture fisheries by weight, according to Jeremy Turner, head of the fishing technology service at the UN's Food and Agriculture Organization.