Tokyo - At Taiji, a quaint whaling town 700 kilometres south of Tokyo, waves lap against steep rocks of a popular national park.

However, visitors are kept well away from the slaughter happening in a secluded lagoon nearby.

Japanese fishermen, backed by the country's government, are slaughtering thousands of dolphins off the coast, while ignoring both international protests and concerns over contaminated dolphin meat being sold to the public.

Between October and April, some 16,000 to more than 20,000 of the animals are killed in the annual hunt, in Taiji and other Japanese fishing towns, often cruelly stabbed with knives, hooks and lances.

The mass slaughter goes ahead with the backing of the government, but without the majority of the population being aware of it.

Part of the marine mammals' flesh is sold in Japan, despite warnings of high-level mercury contamination, animal rights activists said.

"The dolphin meat is highly contaminated," dolphin activist Richard O'Barry said Monday. He sharply criticized Japan's government for keeping both the controversial slaughter and the contamination secret from the Japanese population.

"This is a scandal," said O'Barry, a former trainer of dolphins for the US television series Flipper.

Fishermen disable the dolphin's sense of direction by hammering on metal rods held into the sea, thereby herding them into a lagoon secured by nets.

"It often happens than babies are separated from their mothers and that pregnant dolphins miscarry because they panic," said O'Barry, who regularly travels to Taiji.

Every passerby walking on the road along the lagoon can see the mortal fear of the animals, he said.

"The cruelty happens long before the killing," he added.

Individual, particularly beautiful dolphins are selected in a lagoon with the aid of dolphin trainers and sold off at high profits to aquariums and dolphin shows around the world.

The remaining dolphins are killed in a secluded bay nearby, O'Barry said. The booming dolphin-captivity industry was providing a major financial incentive to keep the brutal hunts going, O'Barry told Deutsche Presse-Agentur dpa.

The former dolphin trainer has been fighting to protect the marine mammals since 1970.

One dolphin can fetch up to 200,000 dollars, O'Barry said, adding that some of the survivors of this year's cull were destined for Germany.

He urged the Switzerland-based World Association of Zoos and Aquariums to monitor its members and bar them from participating in the trade of animals caught in the Taiji hunt. Without international demand, the hunt would lose its allure.

Environmentalists accuse Japan of killing the dolphins and other small whales because they eat many fish. A part of the killed mammals is processed into pet food and fertilizer.

Japan's government justifies the cull as part of the country's whaling tradition and food culture. Activists, on the other hand, argue that only about 1 per cent of the Japanese population eats whale meat, and say only a very small minority of those would consume dolphin meat.

"Most Japanese have never heard of it," said O'Barry. He warned against condemning the Japanese public as a whole for condoning the cruelty, as only a few people profit from the dolphin business.

But he criticized the country's media, which keep mum about the annual slaughter, despite studies that showed the mercury content in dolphin meat to be higher than in fish from Minamata.

In the western city of Minamata, thousands died in the 1950s as a result of mercury-contaminated wastewater from a chemical plant entering the bay.

Like then, the Japanese government is now also covering up the issue, O'Barry said, calling Taiji was a new Minamata.

After one lawmaker in the regional parliament of Taiji made the contamination public, dolphin meat was removed from school menus.

But now it was sold in other parts of the country, claimed O'Barry who fights against the "secret dolphin genocide" as a member of Safe Japan Dolphins, a coalition of animal rights activist groups.

Yet he remains hopeful about being able to stop the killing soon. Activists secretly filmed a movie in the Taiji lagoons, which is to be presented in January 2009 at the Sundance Film Festival.

O'Barry said he hopes the shocking movie, which shows the dolphin slaughter in great detail, will cause a similar reaction as Al Gore's An Inconvenient Truth did for climate change.