NANNING, March 12 (Xinhua) -- 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 scientists confirmed that a pod of more than 20 Bryde's whales was frequently spotted near the island, 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.

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.

Whales are placed under state protection in China.