Several photos posted to Facebook on Thursday appear to show a group of young Vietnamese fishermen teeming with excitement as they slaughter a dolphin, prompting local maritime protection authorities to investigate the case.

According to photos seen by Tuoi Tre News, at least five fishermen gleefully posed alongside the dolphin aboard their fishing boat before beheading and slaughtering the helpless animal.

In one of the cruel photos, two men are seen sitting on the dolphin, while another holds its mouth. One photo shows the cut body parts and internal organs of the dolphin, and another, the beheaded animal.

The Facebook user who shared the photos claimed that the fishermen are based on Phu Quoc Island, off the southern province of Kien Giang.

Other users who commented on the viral post claim to know the men and say they might be residents of the Ward 3, Duong Dong Town on the island, also a famed tourist destination.

Ha The Phong, director of the Phu Quoc maritime protection agency, told Tuoi Tre on Thursday he has been briefed on the case.

“First we will verify if the incident really happened in Phu Quoc waters,” he said. “If that is the case we will call on authorities to sanction the involved fishermen.”

Phong explained that dolphin, together with sea turtle and dugong, are endangered animals and under strict protection on Phu Quoc.

“Dolphins play an important role in the spiritual life of Vietnamese fishermen, so the acts of the men in the photos are unacceptable,” he pressed.

There is quite a large population of dolphins in the waters surrounding Phu Quoc Island, with local fishermen showing high regard for the animals, even calling them ‘sir’ to pay their respects.

Whenever a dead dolphin is washed ashore, local fishermen will hold funeral for it and take its bones to altars built along the beach.