NANNING - Police in South China's Guangxi Zhuang autonomous region have detained four people for their roles in the capture and sale of a whale shark, a species under state protection.

On May 7, photos were posted online of a shark being pulled from the sea off Beihai city's Weizhou Island, prompting a police investigation.

A spokesperson for Beihai police said on Sunday that those detained were the captain and owner of a fishing boat and two others who bought the shark.

The captain and owner of the boat "Yuelianyu 12888" were apprehended when law enforcers boarded the vessel on Saturday, after the captain refused to approach the shore as directed by police.

Captain Qiu said he saw a gill net in the water on May 5 and when the crew pulled it aboard they found a "big fish" caught in it.

Qiu claimed the fish was dead and stank when they brought it on board, and that he had no idea that it was a protected animal.

When the boat arrived at Beihai Port on May 7, the crew sold the net for 2,200 yuan (about $340) and the boat owner sold the 370-kg shark for two yuan per kg to a buyer known as Liao, who sold it on to Huang for five yuan per kg. Huang is alleged to have turned the meat into fertilizer and sold it.

Whale shark is considered "vulnerable" by the International Union for Conservation of Nature and is a Class-B protected species in China. They are frequently seen in waters off Guangxi and Guangdong in May and June.