Twenty dolphins were slaughtered on Friday in the southwestern Japanese town of Taiji, marking the beginning of the cove’s infamous annual dolphin hunt, according to local media, Agence France-Presse reports.

The hunt has attracted global condemnation since 2009, when it was featured in the Academy Award-winning documentary The Cove, which depicted how fishermen round up some 1,000 dolphins a year to sell to marine parks or kill for meat. The slaughter turns the cove red with blood. In 2015, the Japanese Association of Zoos and Aquariums banned the buying and selling of dolphins from the controversial hunt, after protests and pressure from the World Association of Zoos and Aquariums, a global industry organization. (Pictures: Scenes from the Taiji Roundup)

"For several days the hunters have been pursuing pods offshore, who were able to escape capture," said Ric O'Barry, the founder of the Dolphin Project, in an email. "This pod of Risso's dolphins was not so lucky. The senseless slaughter of the adult dolphins, while forcing the young to fend for themselves in the open sea, should serve as a call to action for everyone."

For this year’s hunt, which runs from September until March, the Japanese government set a kill quota of 1,820 dolphins of various species, according to the Dolphin Project, about the same as last year. In addition, trainers will be allowed to choose about 150 live bottlenose dolphins, which have been pre-sold to marine parks around the world. Many more dolphins are likely injured or killed than what is officially reported, the organization adds.

View Images Dolphins are seen at a cove in Taiji in 2014. The annual dolphin hunt has sparked worldwide protests since the 2009 documentary The Cove revealed the slaughter. Photograph by Adrian Mylne, Reuters

Advocates around the world protested on September 1, decrying the cruel nature of the hunt.

“The killing of dolphins is indefensible given our scientific knowledge of dolphins, which has demonstrated their sophisticated cognitive abilities including self and social awareness,” Diana Reiss, a Hunter College psychologist who studies dolphin behavior and advised The Cove, told New Scientist in 2013.

Conservationists hope the spotlight of the 2020 Olympics will encourage the government to ban the hunts.

"We are urging the Japanese government to consider the global spotlight on Japan for the 2020 Tokyo Olympics and end the dolphin hunts and their whaling activity," said Mark Palmer, the associate director of the marine mammals project at the nonprofit Earth Island Institute.

Learn more from our past coverage of the Taiji dolphin hunt: