A 50-kilogram tuna lies on the white floor tiles of Intimas, a fish-processing factory on the Indonesian island of Bali.

The tuna's eyes stare into nothingness. It's dead, but its lifeless body is surrounded by hectic activity. This is the factory's quality-control room.

"The freshest produce with the best, reddest meat is immediately flown to Japan," the manager said.

Tuna is a globally booming business, and the Japanese especially crave the meat.

But to dish up tuna and other seafood delicacies, millions of other fish die each year. Whales, dolphins, crustaceans and turtles become the "by-catch."

The word describes any marine creatures other than those targeted that get entangled in fishing nets or unwittingly bite into fishing hooks.

Marine biologists have sounded the alarm on by-catch as the world's oceans become overfished and species are threatened with extinction.

The conservation group WWF, or the World Wide Fund for Nature, estimated that about 250,000 turtles alone end up as by-catch each year, and for each kilogram of harvested prawns, up to 40 kilograms of by-catch might end up in the nets.

"Every two minutes, an ensnared dolphin or whale dies inadvertently," the WWF's Amanda Nickson said. "Worldwide, the by-catch each year is estimated at 7 [million] to 30 million tons."

Most of the by-catch is dumped dead back into the oceans.

Indonesian activists and tuna fishermen in Bali have now started to cooperate to prevent by-catch with an emphasis on saving turtles.

With an annual harvest of about half a million tons, Indonesia is the world's second-largest tuna producer after Japan, and Bali is home to the country's second-largest tuna-fishing fleet.

The fish are caught with lines up to 100 kilometres long, to which up to 2,000 baited hooks are attached.

Turtles often swallow the bait and then die in agony because the hooks hold them underwater and they can't return to the ocean's surface to breathe.

The Bali fleet is now experimenting with a different type of hook, circular ones instead of the traditional J-shaped devices. The new hooks are so wide that turtles do not swallow them, and tests have been promising so far.

The WWF reported that tests with 1,300 fishermen in the eastern Pacific showed that 89-per-cent fewer turtles were caught. Of the turtles that did bite, about 95 per cent could be saved and survived.

Laode Mongsidik, 54, captain of the tuna trawler Samodra, started using the new hooks together with the traditional ones some time ago.

"During my first trip with the new hooks, I caught 126 tuna, 80 on the new hooks and 46 on the old ones," he said.

Another advantage of the new hooks with their rounded and sturdier design is that large, heavy catch doesn't escape by deforming the hooks and tearing them off the line as often happened with the older hooks.

More captains, encouraged by their colleagues' success, have decided to increasingly use the new hooks.

While these efforts to protect sea turtles might be a step in the right direction, a lot still needs to be done.

Only 15 per cent of the global tuna catch is harvested using the line-and-hook method while 58 per cent is caught with purse seine nets, which trap entire tuna schools - and also by-catch.

Captain Subadri - who was unloading his tuna catch at Intimas, cross because it came in at 4 tons, 1 ton less than he had expected - pointed to another problem: "There are simply too many boots at sea."

Indonesia is giving out more fishing licenses, and as a result, it brings in 300 million dollars per year today from its tuna exports, compared with 20 million dollars in 1986.

Ahmed Fauzi, an environmental economist at Bogor Agricultural University in West Java, said overfishing is a huge problem.

Indonesia's government determined two years ago that 6.4 million tons of fish could be caught each year without decimating fishing stocks, but the actual catch is about 4.5 million tons, so Indonesia continues to invest in expanding its fishing industry.

Fauzi warned, however, that the estimate of the national catch is a "naive assessment."

"In addition to the 4.5 million tons, there is 2 million tons of by-catch and 2 million tons of illegal fishing," he said.