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Fishermen in the small Japanese town of Taiji have begun their annual dolphin drive, capturing and killing hundreds of animals in a government-sanctioned hunt that has sparked international outrage since its portrayal in the 2009 Oscar-winning documentary “The Cove.”

After driving the dolphins into a cove, fishermen drag them to the shoreline, drive a sharp spike into their spinal cords, and butcher them for human consumption.

Some are kept alive to be sold to aquariums around the world, although the Japanese Association of Zoos and Aquariums agreed in May to stop sourcing dolphins from Taiji.

“During this season, hundreds of sentient, intelligent, communicative animals will be killed in an astonishingly brutal way, and that includes males, females and calves,” said Hardy Jones, a filmmaker and activist who began documenting dolphin hunts in Japan in the 1970s.

The Taiji hunt may be the best known, but other dolphin slaughters — some much larger — regularly take place around the globe beyond the glare of cameras.

While dolphin hunting in Japan is on the decline — the Taiji hunt caught about 800 animals last year, compared to more than 2,000 in 2003 — it appears to be on the rise in other parts of the world.

Exclusive video shared with NBC News provides graphic new evidence that Peruvian fishermen regularly slaughter dolphins for use as shark bait, an illegal practice that, according to activists, kills up to 15,000 a year.

In a risky undercover operation in 2013, Peruvian conservation group Mundo Azul documented shark fishermen harpooning dolphins, hoisting them on board and slicing them up — sometimes while still alive. The fishermen use the meat to lure sharks, which they sell on the Asian market, the group says.

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Stefan Austermühle, executive director of Mundo Azul, said he wept when he saw photots of the slaughtered dolphins. “And I can tell you that has not happened to me before," said Austermühle, who has worked on dolphin conservation for 30 years.

Biologists monitoring Peruvian fishermen also documented them using dolphins for shark bait in a 2010 study.

Unlike Japan, where the government permits a specified number to be hunted each year, Peru made killing dolphins a crime punishable by up to three years in prison — but scientists and advocates say the law is poorly enforced.

Austermühle says the easiest way to curtail the slaughter, which is carried out small, unregistered boats miles out at sea, is to ban the special harpoon used to spear dolphins alongside the boat.

"If you prohibit the harpoon, you can't kill the dolphins,” Austermühle said. “They are too fast, they are too small, and you need to have them right there."

The Peruvian Ministry of Production said in statement that since 2013 it “has implemented various controls to safeguard legally protected species whose hunting is punishable by law,” including confiscating dolphin meat sold in markets.

Lawmakers there are discussing amendments to the 1996 dolphin protection law that would prohibit the use of dolphins for bait fishing, prohibit the use of harpoons, and potentially allow the hunting of dolphins to be punished by up to four years in prison, the ministry said.

In Japan, Taiji Mayor Kazutaka Sangen declared in May that the hunt would continue despite the aquarium group’s moratorium.

Some activists hope the hunt will no longer be economically viable if the country’s 50-odd aquariums abide by their pledge not to buy Taiji dolphins, which sell for $100,000 or more. But China, Russia and other nations also pay top dollar for the animals.

An official with the Taiji town government told NBC News that it must protect the livelihood of its citizens, including the fishermen, but it could not comment further because it does not enforce fishing regulations.

The regional government of Wakayama Prefecture referred to a lengthy statement on its website, which says dolphins "can be harvested in a sustainable manner under proper management,” and that permit numbers are set based on scientific evidence. It also calls the dolphin fishery part of the "local traditional culture.”

Fishermen in wetsuits hunt dolphins at a cove in Taiji, western Japan, January 20, 2014. Adrian Mylne / Reuters

The main dolphin species hunted in Japan and Peru, including bottlenose and Risso’s, are not at risk of extinction worldwide, but scientists say they could disappear in places where they are hunted aggressively. A large dolphin hunt off Japan’s Iki Island ended after the animals stopped showing up, activists say.

Dolphins and other toothed whales everywhere are already under threat from fishing nets, loss of habitat and prey, and climate change, said Randall Reeves, an expert with the International Union for the Conservation of Nature, which compiles the Red List of threatened species. At the same time, dolphins reproduce slowly.

“So from the outset, they're just the wrong thing to hunt if you are going to hunt something to survive,” Reeves said, referring to the 100-plus communities around the world known to eat marine mammals — a practice that's growing in some regions, including West Africa.

Killing dolphins as bait to catch sharks, which are also on the decline, Reeves added, “seems to be flawed in so many ways that it's objectionable on more than just humane grounds.”

Ric O’Barry, the dolphin trainer turned activist featured in “The Cove," calls dolphins "a microcosm of our relationship with nature."

"They're like a reference point," he said. "You want to see what we're doing to the world, take a look at the dolphins. There's no point in saving dolphins without saving their habitat. But you have to start somewhere, and we start with dolphins."

On Monday night, O'Barry was arrested in the town of Nachikatsuura, which is near Taiji, for allegedly not having a passport, Japanese police told local media.