NBCNews.com -- Japanese fishermen drove a large group of dolphins into the shallows on Tuesday and, hiding from reporters and TV cameras behind a tarpaulin, killed at least 30 as the annual dolphin hunt that sparked protest in the West entered its final stages.
Both the U.S. and British ambassadors to Japan have strongly criticized the "drive killings" of dolphins citing the "terrible suffering" inflicted on the marine mammals.
Every year the fishermen of Taiji, in western Wakayama prefecture, drive hundreds of dolphins into a cove, select some for sale to marine parks, release some and kill the rest for meat.
On Tuesday, at least 30 dolphins out of the group of more than 200 held in the cove since Friday were herded by boat engines and nets into a killing area of the Taiji cove.
Fishermen waiting in the shallow waters by the shore, some in wet suits with snorkeling masks on their faces, wrestled the dolphins into submission and tied their tails with ropes to stop them from escaping.
Before the killing began, fishermen pulled a tarpaulin in front of the cove to prevent activists and reporters from seeing the killing. A large pool of blood seeped under the tarpaulin and spread across the cove.
"A metal rod was stabbed into their spinal cord, where they were left to bleed out, suffocate and die. After a traumatic four days held captive in the killing cove, they experienced violent captive selection, being separated from their family, and then eventually were killed today," Sea Shepherd Conservation Society activist Melissa Sehgal told Reuters.
The annual hunt has long been a source of controversy and was the topic of "The Cove", an Oscar-winning documentary that brought Taiji into the international spotlight.
Activists say that out of this year's group more than 50 dolphins were driven away to be sold to aquariums. Those not killed on Tuesday were released, they said.
"UK opposes all forms of dolphin and porpoise drives; they cause terrible suffering. We regularly raise (the issue) with Japan," said the British Ambassador to Japan, Timothy Hitchens, in a tweet on Monday. Caroline Kennedy, the U.S. envoy to Tokyo, has also said she was "deeply concerned" about the hunt.
Japan maintains that killing dolphins is not banned under any international treaty and that the animals are not endangered.
Yoshinobu Nisaka, the governor of Wakayama prefecture where Taiji is located, rejected Kennedy's concerns.
"Dietary culture varies and it is the wisdom of civilization to mutually respect other standpoints unless the world faces a lack of resources," Nisaka was quoted by Kyodo news agency as telling reporters.
The Taiji fishing union rejected Reuters requests for comment.
The dolphin hunting season runs yearly from September to March. Sea Shepherd said around 600 marine mammals had been killed this season before Tuesday's slaughter.
Monitoring is difficult, with fishermen erecting tarpaulins over their killing area and blocking access to the cove.