(Photo: chinanews.com)

South China's Guangxi Zhuang Autonomous Region has started regular marine patrols to protect a herd of whales that have returned after decades of absence.

The tourism authority of Weizhou Island on Monday launched the patrols together with coast guards to target illegal hunting and killing of the whales. The patrols will continue on a regular basis, it told Xinhua.

The action came after a pod of more than 20 Bryde's whales have been frequently spotted near the island since last year, indicating an improving marine ecosystem under China's stricter pollution control.

This is the first time that such a whale herd has been found frequenting an offshore area of the Chinese mainland since 1980, said Chen Bingyao, associate professor of life sciences at Nanjing Normal University, whose team spotted the marine mammals during a survey last year.

"Whales are a top ocean predator and a barometer of a marine ecosystem's health," Chen said.

In a widely-circulated video clip filmed by Chen's institute, a giant whale jumps out of the sea and sprays water.

The scientist said the whales, the largest being 12 meters long, are active in the sea area around the island between December and May, attracted by the good water quality and abundant prey.

Since last spring, fishermen and tourists on Weizhou Island, a tourist boomtown, have reported seeing the whales on multiple occasions.

"The whales I saw yesterday were only 200 meters away," said Deng Keshun, a local fisherman, who said the whales usually appear around noon.

Lin Deguang, director of the island's tourist zone administration, said the city government of Beihai, which administers Weizhou, set up a protection zone for whales in July last year and that they will continue the efforts to protect marine biodiversity.

Weizhou Island, located in the Beibu Gulf, is the largest and youngest volcanic island in China. A national geological park was established on the island in 2004.

Whales are placed under state protection in China.