Fishermen in the small Japanese town of Taiji killed more than two dozen striped dolphins on Thursday, campaigners said, as global outrage over the slaughter grows.

Activists from the militant environmentalist group Sea Shepherd said the hunters were herding the animals into a screened-off area because they wanted to hide what they were doing.

"They continue to use tarps to cover the slaughter, and physically drive the pod under the tarps... to avoid cameras," Melissa Sehgal told AFP by telephone from Taiji.

"You can hear the dolphins splashing below," she said, as the fishermen stab a metal spike into their spinal cords.

"It was approximately 30 dolphins -- striped dolphins -- that were all slaughtered this morning."

Boats search the open ocean off Japan's Pacific coast for pods of dolphins. When a group is located the fishermen drive them towards the cove by banging on submerged metal poles attached to their boat.

This creates a sonar wall from which they flee. By positioning several boats in an arc, the hunters can funnel the creatures into a small bay. Once there, nets are strung across the mouth of the cove to prevent the dolphins' escape.

Activists say the pod can be kept there for several days while some of the more attractive dolphins are selected for sale to aquariums and dolphinariums, who are prepared to pay handsomely for a prime specimen.

Many of the rest are killed for their meat, which features in the diets of a small number of coastal communities in rural Japan. It is not widely consumed and the Japanese government recommends limiting intake because of the high levels of mercury it contains.

"Over 1,200 dolphins have been driven into the cove since September 1, when the season began," Sehgal said. "Of those 1,200, over 600 dolphins have been slaughtered, not including today, and 149 have been taken captive."

Local defenders of the hunt say it is a tradition and point out that the animals it targets are not endangered. They say Western objections are hypocritical and ignore the vastly larger number of cows, pigs and sheep butchered to satisfy demand elsewhere.

An official from the fishermen's association in Taiji acknowledged that striped dolphins had been killed Thursday and defended the hunters' decision to screen it off.

He said the butchery was not done in the open for the same reason that abattoirs do not invite cameras into places where land mammals are killed for human consumption, but insisted that the methods were just as humane.

"It has reached the levels equivalent to those of cows and pigs," he said. "We don't let the dolphins bleed and suffer for a long time like before," he told AFP.

The official, who declined to be named, rejected activists' claims that the town maintains the dolphin hunt out of greed.

"You should come and see the way we live here," he said. "I have to question why they don't attack the killing of kangaroos or people who hunt deer for fun.

"This is how we make a living."