Story highlights Fishermen have taken 37 bottlenose dolphins to be sold into captivity, conservationists say 
 
 Many of the 200 dolphins still in the cove in Taiji, Japan, will be slaughtered, they say 
 
 Local officials have previously defended hunting of dolphins as a traditional practice 
 
 Environmental activists say dolphin meat contains dangerously high levels of mercury 
 
 More than 200 bottlenose dolphins spent a second day penned in a cove by Japanese fishermen, U.S. conservationists said Sunday, many of them stressed and bloodied from their attempts to escape. 
 
 The dolphins will spend a third night without food or rest in Taiji Cove before the fishermen likely start to slaughter them Monday for meat, the Sea Shepherd Conservation Society said. 
 
 Until now, the fishermen have focused on selecting dolphins to be sold into captivity at marine parks and aquariums in Japan and overseas, the conservation group said. 
 
 Twenty-five dolphins, including a rare albino calf, were taken on Saturday "to a lifetime of imprisonment," and another 12 on Sunday, the group said. Two dolphins have died in the process. 
 
 Environmental activists have been monitoring activities in the cove in southwest Japan, which is a focal point of the Taiji community's annual dolphin hunting season. 
 
 Although the hunting of dolphins is widely condemned in the west, Japanese defend the practice as a local custom -- and say it is no different to the slaughter of other animals for meat. 
 
 Caroline Kennedy, the recently installed U.S. ambassador to Japan, tweeted that she is "deeply concerned by inhumaneness of drive hunt dolphin killing." 
 
 The Sea Shepherd Conservation Society has been live-streaming video of events in the cove and posting frequent updates on Twitter. 
 
 "Many of the 200+ Bottlenose dolphins who are in still the cove are visibly bloody & injured from their attempts to escape the killers," one update Sunday said. 
 
 Another appealed for people to do their part to end the demand for dolphins captured from the wild. 
 
 "Dolphin slaughter in Taiji continues because of the captive trade. Please do not support aquariums & parks with marine mammals," it said. 
 
 Opinion: Eat fish, kill a dolphin? 
 
 Slaughter under tarpaulins 
 
 The dolphins earmarked for slaughter include those with nicks or markings which make them less desirable as captives. 
 
 The Sea Shepherd Conservation Society described how about 40 to 60 local fishermen work with nets to divide up the pod, whose initial numbers were estimated by the group at more than 250. 
 
 "They tighten up the nets to bring each sub-group together then the skiffs push them toward the tarps. Under the tarps in the shallows is where the trainers work with the killers to select the 'prettiest' dolphins which will sell and make the best pay day for the hunters," the group said. 
 
 "But the process is brutal and stressful. Some of them die from injuries incurred during the manhandling or simply the stress." 
 
 Once the slaughter begins, it will turn the water in the cove red with blood, as documented in footage captured by the Sea Shepherd Conservation Society in the past. 
 
 The fishermen will "kill the 'undesirable' dolphins (those with nicks and scars) under the tarps to hide from our cameras when that time comes," the group said. 
 
 Officials say criticism is biased, unfair 
 
 CNN has been unable to reach anyone at the town office for Taiji, a community of about 3,000 that juts into the Pacific Ocean, or the local fishermen's union for comment. 
 
 But local officials have reacted angrily in the past to Western criticism of what they say is a traditional practice dating back centuries. 
 
 A 2009 Oscar-nominated documentary film, "The Cove," brought the issue of dolphin hunting in Taiji to the fore with bloody scenes of dolphin slaughter. 
 
 The Wakayama Prefecture, where Taiji is, condemned the film in an online response as distorted, biased and unfair to the fishermen. 
 
 "The Taiji dolphin fishery has been a target of repeated psychological harassment and interference by aggressive foreign animal protection organizations," it said. 
 
 "Taiji dolphin fishermen are just conducting a legal fishing activity in their traditional way in full accordance with regulations and rules under the supervision of both the national and the prefectural governments. Therefore, we believe there are no reasons to criticize the Taiji dolphin fishery." 
 
 The Japanese practice of whale hunting has also put it in conflict with the views of much of the world. 
 
 Japan's fleet carries out an annual whale hunt despite a worldwide moratorium, taking advantage of a loophole in the law that permits the killing of the mammals for scientific research. Whale meat is commonly available for consumption in Japan. 
 
 Environmental activists warn that dolphin meat, also sold for consumption in Japan, contains dangerously high levels of mercury and other toxins. 
 
 CNN first learned about this story through a CNN iReport posted by Martha Brock, an environmental attorney and activist in Georgia. "There are activists around the world that are calling the embassy and the press, but I knew I couldn't do much, so I wrote this iReport," she said. ||||| Read this article in Spanish 
 
 Tokyo, Japan (CNN) -- The slaughter of bottlenose dolphins in an infamous Japanese cove took place on Tuesday. 
 
 About 500 dolphins were driven into the cove this year, a larger number than usual, according to the local Taiji fishermen's union. A fisherman who is a union board member, and who did not want to be named, told CNN that the total number of dolphins to be captured or slaughtered was less than 100, and that the rest would be released. 
 
 The yearly event is a focal point of the Taiji community's dolphin hunting season, which many in the community in southwest Japan view as a long-held tradition. The annual hunting season begins in September and runs through March, according to animal rights activists. 
 
 But the hunt is heavily scrutinized by environmental activists, who have been monitoring activities and livestreaming and tweeting about the latest developments. 
 
 In recent days, environmentalist group the Sea Shepherd Conservation Society has provided livestreams showing bottlenose dolphins splashing frantically as they tried to escape their human captors. Dolphins separated by nets into smaller partitions bobbed up and down, trying to reach other members of their pod. The group said that the dolphins appeared bloodied, and had had nothing to eat since their capture in Taiji Cove four days ago. 
 
 The union representative said that the fishermen had introduced what they considered a "more humane" method of slaughtering the dolphins, cutting their spines on the beach to kill the animals more swiftly and cause them less pain. 
 
 Defending tradition 
 
 Although the hunting of dolphins is widely condemned in the West, many in Japan defend the practice as a local custom -- and say it is no different to the slaughter of other animals for meat. 
 
 Chief Cabinet Secretary Yoshihide Suga told reporters at a news conference Monday that marine mammals including dolphins were "very important water resources." 
 
 "Dolphin fishing is one of traditional fishing forms of our country and is carried out appropriately in accordance with the law. Dolphin is not covered by the International Whaling Commission control and it's controlled under responsibility of each country." 
 
 Taiji mayor Kazutaka Sangen echoed the sentiments. 
 
 "We have fishermen in our community and they are exercising their fishing rights," he said. "We feel that we need to protect our residents against the criticisms." 
 
 He accused the Sea Shepherd of using the issue of dolphin hunting to raise funds and attract attention. The Sea Shepherd Conservation Society has been live-streaming video of events in the cove and posting frequent updates on Twitter. 
 
 The Wakayama Prefectural Government, where Taiji is located, gives an annual "catching quota." This year, the government allows for the hunting of 2,026 small porpoises and dolphins (557 are for bottlenose dolphins). 
 
 The dolphin hunt has seen some changes, Sangen said. The town wants to create a whale/porpoise study with the aim of bringing a marine park to the city. And the method of hunting has been changing, becoming less crude, he added. 
 
 On Monday, the fishermen focused on selecting dolphins to be sold into captivity at marine parks and aquariums in Japan and overseas, the conservation group said. Trainers marked the dolphins deemed unsuitable for captivity, which would be either killed or driven back out to the ocean, according to the Sea Shepherd group. 
 
 Kennedy's tweet met with criticism in Japan 
 
 Caroline Kennedy, the recently installed U.S. ambassador to Japan, tweeted that she is "deeply concerned by inhumaneness of drive hunt dolphin killing." 
 
 "I understand her statement as an expression of her concern on this debate," said Sangen. "There always are the people who say it's wrong and it's right, but what we have to see is if fishermen are hunting endangered species or not. They don't. We are fishing under the permission just like the U.S. does." 
 
 While Japanese media did not cover the dolphin hunt, several outlets reported on Kennedy's comments. On social media, Japanese users blasted Kennedy for commenting on what many consider a tradition. 
 
 One user, named @simaya tweeted: "She refers to humanitarian treatment to animals. What about the atomic bombing, Agent Orange and missiles falling on civilians in the Middle East?" 
 
 Masayhisa Sato, a Japanese lawmaker tweeted: "The dolphin hunt is also a traditional fishing culture. I wonder whether it's appropriate for ambassador to comment on this." 
 
 Captivity, death or freedom 
 
 On the days leading to the killing, divers and boats drove the dolphins into increasingly small segments of the water to select the ones that will be held in captivity. 
 
 In the days leading up to the dolphin hunting, 40 to 60 local fishermen worked with nets to divide up the dolphin pod. 
 
 "They tighten up the nets to bring each sub-group together then the skiffs push them toward the tarps. Under the tarps in the shallows is where the trainers work with the killers to select the 'prettiest' dolphins which will sell and make the best pay day for the hunters," said the Sea Shepherd Conservation Society. 
 
 Dozens of men circled around dolphins pinning them against a boat and hoisting them into black nets by pulling on their dorsal fin. When men successfully captured the dolphins into the net, they cheered "Yay!" 
 
 The Cove Guardians counted 51 bottlenose dolphins taken in the last few days, but the fishermen's union did not disclose the number of dolphins captured or killed. 
 
 Japan at center of controversy 
 
 A 2009 Oscar-nominated documentary film, "The Cove," brought the issue of dolphin hunting in Taiji to the fore with bloody scenes of dolphin slaughter. 
 
 The prefecture government has condemned the film in an online response as distorted, biased and unfair to the fishermen. "'The Cove' filmed secretly the scenes of dying dolphins, and depicted their death in a manner designed to excite outrage," according to the Wakayama Prefecture statement. 
 
 "The Taiji dolphin fishery has been a target of repeated psychological harassment and interference by aggressive foreign animal protection organizations," it said. 
 
 The Japanese practice of whale hunting has also put it in conflict with the views of much of the world. 
 
 Earlier this year, Sea Shepherd said it had chased Japan's whalers out of Antarctic waters. Japan's fleet carries out an annual whale hunt despite a worldwide moratorium, taking advantage of a loophole in the law that permits the killing of the mammals for scientific research. Whale meat is commonly available for consumption in Japan. 
 
 READ: Dolphins to be slaughtered, conservationists warned 
 
 READ: Opinion: Eat fish, kill a dolphin? 
 
 CNN's Junko Ogura and Laura Smith-Spark contributed to this report. Madison Park reported and wrote from Hong Kong. Yoko Wakatsuki reported from Tokyo. ||||| 1 of 3. Fishermen hunt dolphins in the shallows of a cove in Taiji, western Japan, January 21, 2014. 
 
 TAIJI, Japan (Reuters) - 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. 
 
 (Writing and additional reporting by Antoni Slodkowski; Editing by Nick Macfie)
– More than 200 bottlenose dolphins await their deaths in Japan's Taiji cove—made infamous in 2009 documentary The Cove—and the Sea Shepherd Conservation Society is doing its best to draw attention and outrage to the annual slaughter. As CNN reports, Japanese fishermen herded a pod of 250 or so dolphins into the cove on Friday; a total of 37 dolphins, including an albino calf, have been separated from the larger group to be sold to aquariums, or as Sea Shepherd calls it, "a lifetime of imprisonment." It doesn't sound like a peaceful process: Two dolphins have been killed. Slaughter of the rest, which will be harvested for their meat, is expected to begin tomorrow. Sea Shepherd has been live-streaming video and tweeting from Taiji, with one update today reading, "Many of the 200+ Bottlenose dolphins who are in still the cove are visibly bloody & injured from their attempts to escape the killers." They've attracted the attention of new US ambassador to Japan Caroline Kennedy, who tweeted that she was "deeply concerned by inhumaneness of drive hunt dolphin killing."